All you need to know about Linear PSU (Power Supplies) To Build And Fix Stuff - Tutorial Guide

this video just requires a short introduction so i had an idea in mind to build a little power supply plus a minus output so give me plus or minus 15 or plus or minus 12. and because linear transformers are hard to get these days even on that expressive expensive and it's not common to find switch mode power supply small ones with a positive and negative output i thought i could make one out of salvage parts and you know what i thought after the last video i could make one out of a battery charger so okay we know a battery charger is only a positive supply rail and i thought hey you know what i can make a plus and minor supply rail out of this so i had a go at it nice little project and this is like reminiscent of stuff i was building when i started as a teenager back in the 70s building little projects and they usually didn't work and you know what i build little projects now and this usually didn't work either but i'm a bit more experienced now i can get them to work i can find out what's wrong with it so this is morphed a little bit i think now it's a really nice little beginners video this will teach you a few things one is the advance used to be gained by building little projects like this and two this involves some basic fault finding it uses the ground of your electronics which is called ohm's law but there's not much maths in here very little maths i dislike putting maths and videos unless i have to but i think you'll learn a few things i think this will teach you some very important basic principles if you are a beginner at electronics repair and electronics in general and if you're more experienced i think you might enjoy it anyway so here goes hopefully it's not too long but you never know with me and my videos my idea of not too long is some other people's idea of an epic but let's see hope you enjoyed and i'll see you all soon at the end or should i say soonish hi guys welcome to another learning electronics repair video i was at the car boot cell this weekend and as well as finding an interesting retro pc i was looking out for some of these so those of you who watch the channel regularly or no i made a video repairing a battery charger like one of these and during that process one of the things i discovered is there's a transformer in the one i fixed the linear transformer that had a center tap and then it had a pair of red wires and a pair of blue wires and the pair of red wires was given about plus or minus 12 volts ac and the pair of blue is given about plus or minus 6 volts ac with the center tap as i mentioned so those sort of transformers are really useful and particularly if you want to put some minor supply for an op amp based project if you like building little gadgets and projects which is one of the things i've been doing recently i've kind of rediscovered the interest in doing that yeah and those little transformers are a bit hard to get even on aliexpress they're not cheap you know there seems to be all stuck around but they're not cheap so i thought we could use the transformers out of these things to make little power supplies hopefully regulated power supply may be affixed plus some minus 9 plus or minus 15 something like that or plus or minus 6 plus or minus 12 or even variable power supply if we say wish so you won't get a lot of current out of one of these i mean it's not going to provide a lot of current this is telling you 6.5 watts uh this one is telling me the output oh this is only a 2.5 you know just two batteries so this is probably of no use but we can look inside it's up to 250 milliamps but it's enough for powering little projects i've got in mind the little million meter project that i have work i just want to finish put it into an enclosure with it with a transformer and regulated support so if you were looking at this you remember on the video effectively the power supply inside the transformer gives two positive outputs so you have a positive output supply each side of the charger which will do with a pair of double a or triple a batteries or do it a pp3 and 9 volt battery so you might be thinking well how do we get a plus or minus volt supply out of a transformer that's giving two positive supplies well it's actually quite simple so let's open these up first see what we have inside them and then let's just draw that out on the bit of paper what we're going to do if you're a beginner and you're not sure about this you'll very soon understand how to get the plus and minus supply out of the transformer so i'll open these up and let's see what's inside them now let's see what we can use i've just turned this one upside down by the way otherwise it actually does power four batteries but it doesn't do the pp3 so this may only have effectively a single voltage rail the three charges which i have no idea if they work but i don't actually need them as chargers uh the three chargers she wanted like three euros for them and in the end i wanted to give a six two but she wanted seven and because i wanted to do some interesting projects with them i thought seven euros is okay i mean the transformer itself from aliexpress would probably cost me that much to get the linear transformers and they'd have to wait a month or more while they arrive actually just before i do work inside them let's just try them let's just switch them on so i'll connect them to my currently just in case there's a shorter one of these i don't want it to go bang mostly because i'll just trip out all my computers and cameras i'm sure you'd find it interesting but anyway i'll just uh put my current limits on i'll move the camera where you can see it's on top of the varia sorry this is in the way a little bit magnifier and we'll try so i'm on current limit we'll put the first one there i would imagine because these are such low power devices it probably won't even light up at all yeah so that didn't do anything but there we go maybe it won't maybe these just come on with the batteries charging what's this one do okay doesn't do anything yeah it doesn't seem to draw any current what's this one do i'm not surprised because this is low power things yeah test okay they don't seem to be doing anything normally you should be careful opening up bits of mains powered equipment in case there's any capacitors in here holding a high voltage charge i don't think we have a problem with these because the light bulb never even came on which suggested power didn't go in if the capacitors are charged if they're there it would kind of come on for an instance right then going down but if the capacitors are small it might not do that you might not light up at all visibly okay smaller capacitors can give you less of a zap but a zap is a zap and it still isn't pleasant yeah personally i think these are probably linear power supplies like the other one i had looked at but let's have a look so we'll open this one up first let's see what we have inside it okay a bit stiff okay so it has what we want it has a a transformer yeah does it have a center tapped out this is the question so i can actually get it out of here well we have from what i can see just trace the wires well this is interesting yeah we have a red wire and a black wire here which goes down to the main so that's your mains coming in yeah and then it looks like it has four wires on it you see a pair of yellow a red and a black so we can have one to see how that one's wider so that has one linear transformer but it's not quite the sword i was looking for let's have a look at the other ones this has some weird sort of screwing like a top secret safety type screw there can you see there's like a little uh i'll show you what it has it has one of those i honestly don't see the point of these stupid things i will call them stupid because you get like a little screwdriver kit like this like five euros and you'll have something in here that just does it so why why yeah what's what's the point yeah it's not like the restricted technology you can't just buy the screwdrivers undo let me see what i mean okay so that's out of there this one is saying effectively so it does dc four times which is four batteries i think it's saying 200 milliamps and then it's saying dc4 times 66 milliamps this is the current that the batteries are drawstring this is the charge current i'm sure so this will be for double a batteries and this will be for aaa batteries yeah and then you have dc two times nine point eight fifteen milliamps but i don't believe that is actually the limit of what the transformer can deliver and that is actually the charging current so we'll have a play we'll see if we can figure out how much power this transformer can deliver so we'll take this one out of here this is what i was looking for so it has two white wires it has two red wires this has a black center tap and this is quite a chunky transformer so i'm sure this can deliver more power than it's stated on the charger yeah this will make a nice little dual power supply i'm sure so we have that one let's open the last one up oh again it has these high security screws yeah you need a kgb screwdriver or something to get inside them yeah here we go somebody commented on the video the oh yeah the one about reverse engine kneeling that one yeah i am an intp and i didn't know what an intp was intp personality and you're right i am i'm one yeah and that in itself probably tells you why i'm if i am offended by these screws yeah because they're just illogical and pointless yeah okay so this one doesn't actually want to come apart easily there we go has another fairly chunky transformer in it so same sort of size as that one basically this one's on a pcb mount so this might actually be quite useful to us yeah it has two pairs of diodes uh it has four output connections on the transformer so we can never play with that one as well let's see what this actually does yeah you know that actually looks like a light bulb rather than led can you see it yeah that actually looks like a filament ball let's have a look that's a filament bubble why why switch on it as well okay so we have our three [Music] power supplies yeah we can uh figure out how this one works it's fairly simple but i think the easiest one to play with first is going to be this one so let's build ourselves a plus and minus power supply let's have a look to see what voltages are coming out of our transformer there i've got the kywitz meter again i put the rechargeable batteries in that i charged off the other charger that i fixed yeah just to show it did work so we'll just go to volts and we will select ac we'll switch it on and let's see what we have so if we go from the black wire which will be the center tap or ground effectively to do red ones if we just get a connection up that's the end of the meter probe so if we go from the black lead which is effectively ground we see we have three volts on this one three volts on this one it's giving me less than the other transformer let's have what we have 15 volts on that one and i'm saying the same on this one yeah plus or minus 15. it looks like plus or minus three which is rather well than i hoped for so that's what we have and then you can see by these ones are some rectifier diodes if we go back into dc again we'll go to the black lead and we'll check on the diodes to have an 18 volt supply another 18 volt supply so we know the transformer is working so let's take this apart now let's get some of the parts off it that we're going to use in our project there's a few useful bits on this i mean we have the rectifier diodes and we have some more rectifier diodes here so i'll take those off they can be useful uh looks like we have a couple of transistors so we'll have those uh the leds are always useful to have so we'll take those as well then i'll get these connectors off because underneath here is a chip you see this thing here this thing is like a single in line it's probably an op amp chip so that might be useful another another transistor so i'll get the useful bits off here that we can get on the bench and let's see what we've got i'm sure we can use some of these parts in our project i've taken all the parts i was interested in off here there are some little diodes as well yeah i mean it's possible even one is a zener diode but i have lots of those sort of things so this is what i actually have that i thought was interesting up here that we can use and some of this we can use in this project so we have a little uh switch and on off switch if you like um i like this so we can see it's just a double holder for pp3 batteries but you know if we connected those two together and put a ground wire from here we could have a nice plus of minus 18 volt supply from two batteries yeah how simple is that um we have a chip but somebody scratched all the markings off why is it with these battery chargers that people scratch all the markings off it aren't they like top secret designs or something look at that the microscope it reminds me of some up amps in this package like a single in line like this but we'll see three leds are always really handy so i'm sure we can probably use a couple of these in this project these rectifier diodes um we'll definitely use these because we need some rectifier diodes anyway we can have it to see what they are one and four double one one amp 50 volts uh same we can use these one amp diodes yeah oh i think they're probably all the same so yeah they're gonna get used at least four of them will probably get used yep same so a handful of one and four double ones yeah i that just came off it fell off and it really wanted and then we have a few transistors so well are they voltage regulators have weaker so you can have we've got these all little uh 470 mark 25 volts for pasta don't really need it let's have a look at these transistors and then let's measure our transformer now we've taken off the board and let's figure out how we're going to put this together yeah we have um sd 965 these are all the same what's that nine eight five no nine six five they're all the same we can test one probably little npn transistors uh two sc two seven eight five looks like a two s a there's a one one seven five i think yeah we can check them on the component analyzer i'd say these are npn and pmp and those are all the same and then the last one is this little thing which somebody has scratched the markings off let me see if i can actually see it down the microscope i think we can probably read this one i'll get the torch looks like a n c possibly seven eight nine or something like ah no it ends with a two i think i'm sure it's anc and then seven something two so a little bit of ice oh probably a bit left on this rush no it's dry feed him see if we can figure out what he does as this dries up let it dry out a little bit so see what it reveals yeah here we go a bit odd to read anc could be a seven or a three looks like an eight nine or eight zero something like that we don't need it but i thought some of you guys might be interested to figure out what that actually is okay because we salvaged these diodes and this thing possibly wasn't working we probably should just actually check them first to make sure they're good you can just use the multimeter if you like or you can just use the component analyzer it doesn't really matter so that's a good one and i'm pretty sure all these will be good but we should check yeah you can do it this way or we can do with the multimeter whichever we prefer yeah it would just diode mode and it'll conduct in one direction we probably don't need to test both directions we see a diode junction in one direction we can assume it's good to deal with that the other way in the other direction yeah that's having nothing that way so the black goes to where the stripe is basically that's a diode junction i'll look at this one so we've got some good diodes here we can use yeah that's a good one we could test the transistor at least that the diode junctions are okay with the multimeter and see if the mpl pnp but in this case it's probably easier just to do it this way so we'll stick them on the component analyzer we don't need these transistors i just thought you might be interested to see what we actually have and we can stick with our stash of bits for future use okay npn silicon transistor quite a high gain one so that's one of the sd965s let's just try the other ones so my guess of being an npn's runs this was probably a 2sd 965 i'm guessing last one of this type low battery yep that's a good one and then the other two i'm pretty sure it was a 2sa and a 2sc so one's going to be mpl and pmp i think the 2sa is the pmp but i can't remember without just looking this up so this will certainly towers yeah this will tell us all right so i have to put some batteries in this that's a pmp yeah that's a pmp this is a 2sa yeah it is and it is a 2sa1175 and then this you'd imagine is a complementary probably npn so the same current and voltage ratings just the opposite polarity if you like mpm pmp polarity isn't really the right word but i'm sure you knew what i meant yeah an mpn okay so we have those i don't think we're gonna use them in this project but we have them let's have a look then now we've disconnected the transformer let's power this up and let's measure the voltages that are coming out this once it's disconnected from the pcb i've unsoldered the transformer completely i'm just going to put a terminal block on some wires just bear in mind guys high voltages can be dangerous obviously with the electronics work especially power supplies and such like there's going to be high voltages so this is one of these cases where if you understand the dangers and you respect them you are pretty safe especially on my workbench because i actually have an isolation transformer which means i can accidentally catch hold of either the live or the neutral and i will be perfectly fine as long as i don't catch all the both of them at the same time okay if you wanted to be safer you could put some insulation tape over this or use effect like an inline coupler so the thing is basically covered do this however you are most comfortable with which will no doubt depend on your experience level i'm okay with this i might accept that some people will not be and some people will probably tell me in the comments that i shouldn't be either okay so we have our transformer now before we actually plug it in let's measure the resistance on this so we can see what we actually have the first thing you'll notice the red wires are a bit thicker than the white wires which would suggest that they take a higher current or can supply a higher current yeah normally thicker wires means a higher current i put my meter on ohms range and the black this is the center tap so this is effectively the center of the winding so what we should have here there's a connection from the red each of them to the black maybe with a little bit of resistance depends on the widening so that reads almost zero but transformable one is can read very low almost zero almost zero so we can draw this on a piece of paper i'm gonna measure to the white ones as well so we can draw it all in one go so if we go from the black again that's really 9.6 ohms that's a higher resistance winding now that could be because it's a much higher voltage but it could also be because it's a muscle where we're currently whining so it's effectively thinner wire well basically we have a transformer so on one side is the primary this is going to the in my case 220 or 240 volts ac and we have the secondary now the secondary this is the two red wires and you have the black wire in the center so i'll draw the winding on the transformer like so that's the two red then the center of the wide has a tap on and this is our black okay the two white wires are also connected to this winding and they're either giving more or less voltage than the two reds so they could be tapped off from here and here given a low voltage or there could be additional windings giving a higher voltage so let's have a look to see what they're actually doing now so to measure them we need to go to ac volts so i'll choose volts one touch of a button volts dc select volts ac so i'm on volts ac now the thing with these transformers is the two windings i've just shown the drawing are completely isolated to each other or i should say are completely isolated from each other one winding the primary is in this bobbin and the other ones are in this one so there's no electrical connection across the transformer primary to secondary this is your primary voltage in secondary voltage out so it's quite safe to touch these yeah where it's not safe to touch these so we'll switch it on and now let's have a look what voltage we have so we go to the black one and i can use my fingers this is perfectly safe this has to be red in the circuit about three volts three volts okay and then the white wiring is a much higher voltage 15 yeah 50. so the three volts we read in ac on here maybe will give us 5 volts dc because dc has a peak voltage but this is probably too lower voltage to be useful in our circuits but we can have a week anyway and this plus and minus 15 is a very useful voltage for op amp circuits so let's figure out how we're going to get a plus and minus voltage supply out of our transformer here is our diagram so we can continue with this first we know the white wirings are giving more voltage so what actually happens with our transformer is the white is here and another one is here so basically with a transformer the output voltage depends on the ratio of the number of turns and the winding so basically the primary will have a much higher number of turns in the secondary if you say you had a thousand turns here at 220 volts ac and you had 100 turns on the secondary you get a 10th so you have 220 yen 22 out that's basically how it works so we know the white ones are giving more voltage so they have more turns in the windings so that's what we have so we want to get from this positive and negative surprise and we're going to try and get two suppliers and see what we have to convert the ac into dc you need a rectifier diode and the rectifier diode we've just taken half a dozen of them off the circuit board this is the symbol and they pass current in one direction which if you imagine that's like an arrow pointing this way it passes current that way so in this case only the positive half cycles will come through here yeah and we can put one here this is the lower voltage okay on the other side to get a negative voltage out we need to put the diode the opposite way okay and again we're going to put two of them so we're going to connect four diodes to our transformer like this to do this we'll use a little bit of vero board let's solder this together and let's see what we've got now we could also build this if we wanted to on a bit of breadboard but i want to have this little power supply so we'll do it this way i'm not going to try to make this as small as possible this is meant to be an educational video if we wanted to we we could use a much smaller bit of board but we'll use this piece so i'll just uh clean this solder off this bit of wire then we can start to attach them so i'm going to put the black wire in the middle basically looks like i have to just uh clean the solder off it but i'll get it on here and there we have it i've effectively put the black in the center of the board we can if we arrive we can just draw a line across here good practice just to mark it so we know that this line here is ground okay and then you can see i've put the reds just either side of the white line and the whites just either side of the next white wire so we can see quite clearly where the voltage rails are now there's something i just want to mention that i just neglected to say earlier but it's important so i'll just mention this i was showing on the diagram that the transformer primary and secondary are isolated from each other and with this transformer i can actually see two bobbins in here two sets of warranties so i know visibly really that is the case but you shouldn't trust that especially with cheap electronic devices it's possible you may find a device in what's called an auto transformer in now an auto transformer will step the voltages down in the same way but it will not give you what's called the galvanic isolation the isolation between the prime and secondary therefore although the secondaries have low voltages on you can still get a full means potential shock by touching it and i'll just show you what that is if you come across anything like this it really is not a safe device so i wouldn't expect it but you never know so we're on ohms range if we just measure across the primary you'll see our transformers about 570 ohms as i said the primary winding has a lot more turns in the whitening than the secondary but in any case with the transformer there should be no connection between the primary and any of the secondaries so if we go across here yeah it should be open circuit yeah i suggest especially if you're beginners at this just do check that before you start messing around with little mains transformers i'll show you on the drawing what you may come across just so you can be clear on this so this is our transformer but it's possible you may come across what's called an auto transformer so with an auto transformer effectively you have one big winding just one winding yeah and across here you have your ac mains and then at some point in the winding it could be anywhere really but some point in the winding you'll have a tap another one another one one another one and this could be your white red black red white and from the black if you put your black meter probe on here naught volts you will still see three volts to here you'll still see 15 volts to there and this side as well yeah but the voltages may be the same 15 volts 3 volts 3 volts 15 volts but there's no isolation you haven't got this barrier so although the voltage between the points all the same every point is connected directly to the mains that's called an auto transformer and you really really should not come across that in these sort of consumer devices but really really shouldn't and what might happen to you and not necessarily the same things yeah so just bear that one in mind so now we have our transformer connected to our vario board let's put the rectifier diodes in so we have a little stash of these taken from the charger these are one amp diodes we can assume that these are sufficiently powered to handle the current this can deliver so let's put our diodes in we could start laying them flat and cutting traps but i think i might just do it the easy way if they're long enough to do it so let's see yeah we can fit them in so we put one here and that means on this will be our dc output you see i'm putting the diodes with the stripe towards the voltage rail i want to generate this will generate the positive voltage rails yeah so we have there we have there now on the other side we want to generate the negative voltage rails so in this case it goes the other way around so the stripe goes towards the ac coming in basically that way so it's the opposite way around you see the opposite way around and then we want more that one more that was too short but this one's just the right shape and size so this can go on the other voltage rail okay so we'll put our diodes in i'm just going to straight them up so they're in the same position on each one a bit tired because i have a little bit ocd to be honest let's solder these in place okay that worked quite simple i hope it was in shot and you can see it let's test this now so let's measure what's coming out of this and then let's look on the oscilloscope i want to show you what this is actually doing here here is our voltmeter we now want volts dc then we're going to measure what's coming out of each of these diodes i'll probably have to tune it upside down to actually get on them to be quite honest yeah i can't get to the back end of these ones okay let's do it black we will put in the middle the center tap this is our ground and then we have on this dial coming out 2.3 volts yeah 2.3 volts it's really this one's only reading about 3.6 volts at the moment yeah yeah you might be wondering why minus 1.3 minus and you'd expect it'd be the same as the other side but it's actually kind of a bit all over the place the meter doesn't seem to like that very much yeah this is hard to do the same thing now yeah and this is giving a steady reading let's put our silver screw plate and let's see what it's actually doing i've attached a couple of header pins on this side so i can easily get to this side of the diode without turning the board over i've also soldered one in the middle so i've got a ground point for my oscilloscope or test meter so we can have it now so this is what's coming out on the low voltage winding and you can see we have ac and we go to the other one can i get to it we have an ac signal yeah what comes out of our diodes dc well what actually comes out is this so you can see effectively we're getting the negative half cycle the bumper that's going below the center point center with zero basically yeah and if we go on to the other diode we're getting the positive half cycle you see it and on the higher voltage winding if we just go to the winding we have a much higher voltage ac same on both ends of the winding and coming out of the diode well there's a much larger negative half yeah and the much larger positive half now if you look at the one in the middle the low voltage you'll probably see that can you see that bump isn't half of the voltage yeah it's kind of like less than the top off that's because this is only a low voltage rail and when this diode conducts effectively it loses 0.6 of a volt so we're only getting a bit of a bump there yeah and the same with this one when we look at the high voltage the 0.6 revolt has a lesson of effect so we see pretty much the whole half cycle so there's a couple things we can do first with this first of all we can solve this problem or rather mitigate this problem where we've seen only a small part of the signal here yeah and secondly we can then add some smoothing capacitors to get a proper dc voltage so let me show you how we're going to fix this problem with this being a low voltage pulse not half a cycle to get around this problem we're going to fit what's called schottky diodes so this is one of the 1n401 same as we have and you can see this is the full width voltage drop in diode mode diode mode basically measures the voltage drop not a resistance you see it's 0.567 volts so that's how much voltage has dropped across this diode when it conducts that's why we're not seeing the entire half cycle coming from the secondary and it's notable on the low voltage one these are shot key diodes these are two and a half amp they just want to happen to have and if we look at one of these and we do the same test forward voltage drop is 0.18 so it's much lower so this means more of our half cycle voltage will come through the rectifier which is what we need so let's take out the two from the red ones and let's fit these instead i've changed the diodes now this can confuse beginners because it confused me when i was a lad yeah i used to think that if i connected my electronic project to a car battery which was like 12 volts 80 amps that it was gonna cause the project to explode because my project couldn't handle the 80 amps yeah this is before you understood ohm's law so with these diodes just because i say the 2.5 amp diodes it doesn't mean they will provide 2.5 amps it just means that they have a maximum rating of 2.5 amps that's the maximum they can deliver so these are actually 2.5 amp 40 volts these are 1 amp 50 volts the 50 volts again is a maximum of 18 so it doesn't need 50 volts to work it's just the amount it can withstand we know this is about 15 volts so this is about three or four so that is not a problem yeah that is fine let's connect our oscilloscope again and let's see what it's doing now so i've just got the ground lead we'll switch it on okay so ac half a wave ac and a kind of half a wave yeah that's the or the higher voltage one ac output and this is the other one the low voltage one you get to it ac and the same thing okay it's kind of mostly given as a positive half cycle this is all about experimentation after all so that's interesting it's like this we were seeing effectively what i expected the positive half cycle sorry this one the white one positive half cycle and then on the red ones we were kind of like seeing the positive and then a little bit of the negative uh uh if this we consider to be naught vulture and he was doing the same on the other side so basically the red one was given us a kind of a voltage that was getting a bit positive and then with negative again naught volts was kind of here and then this was effectively just giving us the negative half cycles now this is a kind of a pulsed dc it's not a smooth dc which is what we want so as i just mentioned to fix this we need to put capacitors on here so what we're going to do is we're going to connect from the red this is the positive supply so this way around the electrolytic to there yeah and then from the white we're going to do the same thing yeah that will give us a smooth positive supply here and the capacitor should charge up to the peak voltage so i'm expecting to see more voltage here than we had on the ac the ac being effectively the average of the signal you know the average the root mean square we'll call it the average voltage yeah so that's what i'm expecting then the same on here i'm expecting to see the peak voltage this side is our negative supply so the capacitors go the other way around a negative to the voltage value just draw them in put some dots in and again with this one going to the higher voltage rail okay so what we should now have is a plus and minus supply the value of the capacitance isn't particularly critical and if we're not getting enough smooth there's too much but we can just put two in parallel so i'm going to put in here just because of what i have 2200 microfarads at 16 volts because as you know this is quite a low voltage rail it may even be too low for us to use but we'll have a go and then here i'm going to put 1000 at 25 volts because again it's what i happen to have and we can always put you know more if we need them we may well do but this is quite a low current supply so let's try that to start with i fitted the capacitors here so these the positive output rails the ones with the stripe of the rectifier diode going towards the voltage rail so positive end of this capacitor positive end of this one these are the negative ends so it's the anode of the diode going to the voltage rail so negative negative and then basically the two positives of these and the two negatives of these are all connecting to ground so we now actually have a ground rail and a few places on here so i'll draw them in it just means we don't make any mistakes later so this is actually a ground and we have here a ground and the same here and we can always cut the track to if we want to use this track further or not connected to the ground but if we draw them in now it makes it less likely to make a mistake yeah when you're doing this sort of thing you've actually you know you're putting this together on the fly yeah making it up as we go along here basically is what we're doing so that's that one hand doesn't seem to be working very well i guess i mean i've had these a long time so there we go all right so we should now have four dc output rails let's see what we've got and let's see whether the low voltage one is any use to us i'll do this now from underneath the board i don't think we need the oscilloscope right now we can check for some ripple on the voltage rails once we put a bit of a load on it but let's have a look in fact we'll check them anyway so we'll power our power supply up again okay put the voltmeter on well that's what voltage ones we have so we want volts dc this is ground in the middle and i'm going to measure under the capacitors i took the links out because i don't really need them anymore so ground is here so we have and my we have a 14.3 volt supply and this should be the minus 14.4 volt supply okay and then on the other capacitor this is a minus 4 volt supply and this is a plus four volt supply okay we can now mark our voltages on here so we have plus 14 volts we have 14 volts and then we have uh plus four sorry minus four volts and we have plus four volts these are not really of any particular use to us it's a shame if the transformer had more windings we could get more volts if we could get nine out of these or seven we could make a plus or minus five and we can make i think out of these probably make a nice plus or minus 12 volts so what we need to do now is to make sure we have a stable voltage coming out and to make sure we have a useful voltage coming out and i'm going to see if i can get from this plus and minus 12. now to do this i'm going to use fixed voltage regulators you could use a variable or two variable voltage regulators for that matter but to keep it simple i'm going to use plus and minus volt regulators we can check the data sheet to see if this is all work so what i'm thinking of putting in here 7 8 1 2 which is a positive 12 volt regulator and basically this connects the ground and coming out we have the voltage we require we need to put some more capacitors on this to make it work properly yeah but the idea is to put that there and on this side we'll have a seven nine one two which is a negative 12 volt regulator we'll go like so and we'll go like so that's it we'll need some more capacitors on the output so let's see if we can use these voltage regulators i need to check the data sheet this will tell us whether the 2 volts difference between the input voltage and the output voltage is enough here are our two voltage regulators we have the seven eight one two the seven nine one two the seven eight one two has a pin out and as much as the middle pin is ground the input is on one and the output is on three so this is basically pin one this is pin two and that he's pin three and that to me is sensible if you like it's like the diagram but the seven nine one two doesn't have the same pin out with the seven nine one two the input is on pin two so i make a notice now a diagram the ground is on pin one and the output again is on pin three the same it also says this is a typical example we need to put a one microfarad capacitor close to the input and another 10 microfabric close to the output so we'll do that as well we may also need to fit heatsinks onto these but because this is probably quite a low current supply then we may not these will handle generally one amp up to two amps peak the wattage depends on the voltage drop now the minimum voltage drop is basically 2 volts and we're pushing this a little bit with our design so we might find this just doesn't work reliably and may work better using 7809 which is a 9 volt output and 7 909 to give us a plus and minus 9 which is also useful for off amp circuits but see these are the ones i happen to have and i don't have the nine volt versions let's try it and see i fitted the voltage regulators positive and negative this one the positive one was quite easy to fit so the center pin is ground and then we have in and out so you can see i've just effectively just cut the track here between the in and out so this is the voltage coming in going out and this is one of our ground points now the other one is a little bit to me strange so pin one is ground pin two is in and pin three is out but it's very difficult with this sort of strip board to cut a track directly between two holes i mean you can't do it but it's a bit fiddly so what i've actually done is you'll see we have pin two which is in connecting to the capacitor this is your power coming in and then out as on this one here yeah so we can switch this on now and we can measure the output from our regulators and see if we have what what we expect with these ports and minus 12 volts i'll just get a connection to ground let's switch it on and let's see what we've got so this is our 12 volt regulator here and that has 12.15 volts on and this is our minus 12. and that is minus two and a half that's strange what's on the input of two it's that's pin two what's minus three point three so it appears there's something wrong with us voltage regulator the power comes from the diode here we can just check there just switch it on no we only have 3.3 volts there as well so let's see if we can just figure out what might be wrong with this power supply now and why we don't have the -12 here is our schematic so let's see what we've done we've put a capacitor on here and we've put another one on here the other way around this is positive to this end that is positive to this end because this end is more negative than here so we put those capacitors in and they are the one microfarad this one here these are the big ones we fitted they're all 3300 i believe and this is the one microfibers and then we have another capacitor the little tantalum ones on the output like so and another one here again this is the negative end to the negative and this is the what this is the 10 magnifier and we can see the positive regulator is working and here we have plus 12. well here we don't have we only have about minus two and coming in we only have about minus three so why because we had minus 14 here before why are we getting a low voltage well i think it's fairly obvious certainly if you have a little bit of experience with this that something is dragging this voltage down so if there's not enough voltage coming in you can never have enough voltage going out yeah something's dragging this voltage here down from this diode and really there's only two three ways that could actually happen two or three yeah so let me just explain to you and this applies really to any sort of voltage rail whether it's a supply s or even if it's a logic level on a circuit board an enable signal or something like that you always have the same situation you have the source whether it's coming from a rectifier diode whether it's coming from sort of chip sending out an enable signal or a power good or something like that you have a source and then you have effectively the target the destination the load the load yeah the load could just be another chip where the chip selector or something like whatever pin yeah it could be something like that or in this case it could be something connected to here now we don't have a load but we do have a capacitor on here yeah we have a capacitor here and we have the regulator what we need to look for in this example is paths to ground because something is dragging the voltage down yeah so which components connect from this rail to ground well this capacitor does directly yeah and this chip has a ground pin and an in pin so there is internally a path to ground okay but this chip also supplies the in to the out yeah in out and on out is another path to ground this capacity so conceivably if any of these three components are faulty be reading low resistance or near to a short it would pull this voltage down yeah these two directly and this one indirectly through the chip so one of the possible problems there's always resistance here a little resistance here away resistance here yeah the same as this type of example in this case you would normally have a resistor which is holding this to some sort of voltage level let's say 3.3 volts yeah so normally this signal is high we'll put a line over it which means active load will put the line over here is active so in this case what should happen is this chip should be able to take this signal low or this should be able to take the signal work if the signal is just low when it shouldn't be so effectively whatever inputs on this shouldn't be generating an active work it's still low you have the same situation you could have a shorter way resistance than the source yeah you could have a shorter oil resistance in the load because both of these chips have got connections to the ground internally so there is a path to ground in the chip in the chip and the other possibility is that this resistor could be open circuit so there's nothing to pull it hard yeah so you can see that the various reasons why this could be low and it's not supposed to be if it's always low so if you can understand that and i'm fairly sure even to beginners that's fairly clear yeah if there's no resistance to pull it high it will be low if either he's dragging it down below the same applies to our circuit this applies to any circuit yeah as i said so there's another possibility why this voltage would be low and it's equivalent of this resistor where's the resistor in here well there isn't one exactly but this diode effectively acts like a low value resistor it conducts yeah it conducts that direction and it isn't zero it has a effectively like a little resistance in it a finite resistance yeah where's the current going well the current's going back to ground which is here yeah where's it going through it's going through the coil does the coil have resistance yes so effectively this coil also has if you like an imaginary resistor in it and if that resistor is too high it's the same as this yeah being open circuit or too high so the other reason why the voltage here could be too low is that the source where it's coming from is too high and we call it impedance it's really resistance the reason we call it impedance is a technical term impedance is resistance that varies with frequency yeah so the source could be too high impedance that means it cannot provide enough currents into the circuits to make it work the other thing is that this with the capacitors with the regular with the regulator could be too low impedance it's drawing too much current to ground due to a fault and those are the only two reasons why you can have a low voltage two i impedance source two or impedance load and the same applies to this yeah if there's something wrong with the source effectively it's too high impedance as resistors open it's two high impedance it can't drive the voltage high or this is two other penis and it's holding it down yeah and really guys this is the fundamentals of fort finding if you didn't get it just play that bit back again a little bit later when your brain settled yeah when you had a coffee or a beer but if you grasp this relationship between source impedance and load impedance you will be able to repair a whole load of stuff a lot of stuff will make sense to you once you've grasped this so given that where's our problem why isn't our circuit working well the first easy thing to test and this is probably the easiest thing to test is have we got a low impedance load short or near to a short on the output yeah so let's have a look so this is our output capacitor this is on the output of here let's measure the resistance of grottage well it's kilo ohms yeah it's kilo ohms it's high it's high resistance yeah let's have a look at the input capacitor this is effectively the resistance across the input that's this one yeah do we have a lower resistance to ground let's see so this is the capacitor no we don't it is basically open circuit uh open circuit and this one's into the killer ohms on a high voltage rail i mean a very high voltage rail that may actually be a low load but on a voltage rail of 12 volts it isn't and we can work that out with ohm's law this is the one bit of mass i do on the channel let's figure out if that is the actual world how much current is flowing through the world yeah let's figure it out so for this we need ohm's law always remember ohm's law s draw a triangle v i r yeah you can remember oh this is resistance huh i this is current v this is volts yeah remember which one goes where easy r is on the right resistance is on the right oh oh they both we get with oh yeah v is at the vertice the vertex of the triangle yeah if you remember that you always get it the right way around so if we want another current that's flowing in our world and we know the load's 2.4 kilo ohms or 2400 ohms yeah and we know the voltage and supply 12 volts close enough yeah so we know those values what's the current following well current equals v over r yeah that's what the triangle is for i equals v over r r equals v over i v equals i times r that's the triangle so we can work this out r is always in ohms i is always at amps and v is always in volts let's see how much current we've got and i'm fairly sure you can see 12 divided by 2400 he's got a five in it and it's not a very big number yeah if they taught you mental arithmetic at school to talk to us how to do that let's see so 12 divided by hundred told you'd have a five in it didn't i so this is amps this is 100 milliamps there should be 10 milliamps so that would be five zero zero five that's five milliamps that is the resistance of the load yeah if it's a windy resistance i mean a chip various resistance at voltage it's not when yet but we can see there's no short there isn't going to be much current flowing down through there okay let's compare it with the positive regulator so this one is working so what we've got let the emitter again resistance well actually is higher quite a bit yeah and what's the resistance on the input well that means open this open circuit the same as this one open circuit so yeah this one is a little bit higher but there's no shorts there we don't have a short circuit capacity so have we got a faulty voltage regulator well the way to prove that is to change it that's one way we can change it we can put another one in there so i have a spare one let's change it and let's see what happens i've taken out the suspect voltage regulator the 7912 negative regulator this was a new one the only other one i have is this one which is salvaged from somebody's a pull taken from something or other so i don't 100 know that this is good but let's compare them so we'll go to the ground pin i think on pin one i'll use the positive weak it's a negative regulator let's just check the resistance so that's the resistance to the input and it's about 16 meg and this is the resistance of the output about 5.6 k yeah what's this one meaning well that's effectively open circuit and that's 22k so they definitely read different yeah what's got these middle pins that's 2.37 what's this one 1.7 so they definitely read different does this mean we have a faulty one let's just try diode mode let's see what that means i mean there's no real way you can test these without actually connecting them up well let's compare the comparison can sometimes be good so again we're on diode mode now well that's reading 3.27 3.0 0.56 yeah what's this really 2.2 it's lower 2.2 it's lower and 0.54 so they really different but you can say that for example those two are both giving away readings just one's a lot better than the other no they're very similar they're very similar these are the ones that read differently uh 3.27 two point six nine so this reads lower now bear in mind these are not the same makes this is an st sgs thompson and this one is on semiconductor so although they're both the same device they're not the same make so it's possible the difference of readings are just some internal difference but they both work the same but because you read different let's put this one in our circle let's see what it does just before we do that let's measure these capacitors as well so this is our capacitor on the positive voltage rail and that's reading about two yeah two volts on the diamond ranges it's climbing up it's obviously charging the capacitor it's charging yeah okay that'll probably eventually charge the point where it just reads open okay what's this one doing so this one this is the positive end this is the negative rail well that reads low completely different yeah like this capacitor has a problem let's look at it oh i think now we can see where our problem is with this this is the capacitor on the positive rail and you can see there's a little plus sign just there plus minus this is a positive voltage 12 volts and we know we drew a line up here this is ground so the positive on the capacitor the terminal positive terminal is connected to the positive so look at the other one so the other one you can see what i've done here is i've actually put it in the wrong way around in this case i've put the negative to ground and i've put the positive to the supply rail but this is a minus supply rail so this capacitor is in the wrong way round and i'm sure that's why it's reading this resistance effectively this low voltage and it looks like that is the cause of the problem now we could put it back in the right way round let's see what happens if i actually measure it the right way so the red to the positive does it now just charge up no it doesn't it reads kind of like low in both directions so it looks like that capacitor has been damaged this is the same thing that would happen if we had a work effectively a weekly capacitor or low resistance not short the reason is not short we didn't have zero volts coming out we had a very low voltage coming out so it looks like we've actually damaged that capacitor by putting it in the wrong way around but this is effectively the same thing that would happen if we had a faulty capacity let's change this one i've soldered the voltage regulator back in the original one i was using and i've put the capacitor in the right way around this is a replacement one this is another very important thing really with fault finding change one thing at a time because we found a definite problem here i put the original one of these back in again normally speaking there's only one component causing the fault unless you've had a short circuit it's bloom some others but change one thing at a time in this sort of situation right let's check now so we'll go across our capacitor again positive to negative and now it's reading high yeah it's not reading that loading that's on diode mode so let's power our board back up again and let's see now if we have a plus or minus 12 volt supply okay i'm on ground let's check the minus and we now have a minus 12 and we can go over here and we have a plus 12. so we now have the supply rails we expected you might be wondering why didn't the combustion explode well this really brings us back to this discussion i was having again this capacitor effectively was acting like a near short circuit it was drawing as much current as it could through it but when i say as much current as it's chord is because it's limited by how much current this wider than the transformer could actually supply and we know this is a fairly small transformer it may not even have enough warmth if you like to drive our device i mean i'm hoping to get a few hundred milliamps out of it we'll have to try that very shortly now we've built it but the reason is that it couldn't supply enough voltage for this to explode or get hot so what happened there's the output here was being dragged down by the faulty capacitor yeah this was passing i say a lot compared to how much this can supply it was passing a lot of current into here and so the input voltage went down this is another very important thing that beginners should learn so when you have like a short or a similar condition if you measure the voltage here and you find the voltage here is too low don't think well there's a fork with a diode or something further back yeah the fault can be the other side of something like a voltage regulator so a short on this rail can take this rail down towards ground yeah so always keep that in mind when you're wondering where is the load okay so we've now got our little power supply working fixed output plus and minus 12. so i think the best way to test this to say is how much current can it draw is to put some resistances on the output and basically see how much we can load it before the voltage here drops so how much load should we put in our power supply and how we're going to do it well let's try for a hundred milliamps on both rails first plus and minus 12. let's see if he can do it so i think actually we should all stick one of these on our mat somewhere on our bench somewhere and we can print these out v i r yeah v in volts or in ohms oh yeah amps yeah so what do we want to do well we want to put 100 milliamp load on we know what the volt is it's 12. yeah we know what the current we want is 100 milliamps or 0.1 amps so what resistance do we need well 12 divided by 0.1 i think you can probably easily work that one out is 120 ohms so 120 ohm resistor will give us 100 milliamps there's one other formula we should write in our bit of paper and then we're going to print these out and stick them on my bench yeah watch w equals v times i what's equals voltage times current in volts and then amps again so if we put 100 milliamp load on our power supply at 12 volts what is the wattage well watts equals 12 times 0.1 now 12 times 0.1 is 1.2 watts so we need a resistor 120 ohms and more than 1.2 watts you could get away with a smaller resistor for a very short period of time but if we can find something like a 2 watt resistor let's see what we can find i don't have any 120 ohm resistors apart from sort of quarter watt ones so what i've done is i've actually soldered together a 22 ohm and a 100 ohm just basically using what i have i mean the values are not critical you know we can always put a different load on so we can tag our load on here i'm going to actually just use some crocodile clip leads that's the easy way to do it and then let's see if this will provide 100 milliamps on both rails i've connected the crocodile clip so it's ready to go i just tagged another pin header here so i've got a good ground point we should just make sure our test setup is good so if we measure from ground i can get ground by any of these ground to be honest uh we can just check so we should have 120 ohms from here to this crocodile clip well actually that's really high like i've got a bad connection there somewhere yeah we'll check that one and this one is reading 126 no no it's really okay i must have bad connection noise okay so we have that we can now go to volts and let's see what voltage we get out now on our plus and minus supply rails okay so voltage dc again i'll connect to ground that will do you can switch it on and what have we got 11.3 10.8 so at 100 milliamps this transformer is struggling to supply enough voltage it may be that the input voltage is dropping a little bit too low because we were kind of pushing it yeah we were near to 14 volts coming in and we probably should be 15 or 16 volts to give a little bit of headroom yeah so you can see that 100 milliamps it can can't really quite supply that current now the ways to fix that i mean one would be to get a bigger transformer from some other scrap device another would be to let's say make a nine volt supply plus some minus 9 volts then we have a bit more headroom so we can do that by changing the voltage regulators but there's another way we can improve the efficiency of this which might help to get the 100 milliamp output so let me show that to you and then see what you think what we have here is basically called a half bridge or a half wave rectifier halfway rectifier so we know that when this end here is positive with respect to ground which is here not volts this diode conducts but the signal coming from the transformer is actually a sine wave and it's crossing through zero volts it's getting positive and negative so when it goes positive here we see like i drew we get the positive half cycle and then the negative one is blocked and we get the next positive half cycle and the negative one is blocked yeah continuing so that's what we have here and the same applies here so this diode conducts that way only on the negative half cycle so when this end here is negative with respect to ground we get the negative half cycle so effectively the positive and negative are only getting a half cycle of the waveform they're not getting the fault waveform and there's a way we could actually get around that or they get around that there's a way we can make it more efficient we have the coil okay and we have our diodes and we have nut bolts okay and we know this end effectively here gets the positive half cycles and this end gets the negative half cycles okay so when this end is positive the diode conducts when this end is negative the diode conducts but can we make it so that when either end is positive because it alternatively positive and negative it's ac it conducts yeah we can so what we can do is this we can put another diode from here conducting that way jump over here and go to there okay so when this end is positive this diode conducts when this end is positive this diode conducts so what we've actually got now is we've got both half cycles so the first half cycle comes through this diode i'll try and draw it and scale to this so it makes sense okay okay so the first half cycle comes through this diode yeah and then when this one stops conducting this one starts conducting so we get another half cycle through this diode yeah and then back through this one again and back through this one again so we're getting twice as many positive pulses yeah from the same transformer and we can do the same with the negative as well yeah we've got to do the same with both so we can now take another diode from here this way around yeah we've got to jump over the wire somewhere today okay so can you see now that when this end is negative this diode conducts so we get a negative half cycle and then when this end goes negative this diode conducts and we get another negative half cycle so again we get twice as many if in this case on 50 hertz we'll be getting 50 pulses of seconds we're now getting 100 pulses a second so more current can flow yeah now depending on where the restriction was if this transformer can't provide more current it was doing it may still not give us 100 milliamps but let's try because it's interesting let's see what happens i've fitted those other two diodes i've put some colored wires to make it a little bit more obvious so from this end when this end is the positive end it conducts through the red wire up to here the positive voltage rail and when this end is the negative end you see the diode there why the other way around with the strap towards the pcb it feeds a negative down to this voltage rail so basically now both ends when the positive will connect to here this capacitor and both ends where the negative will connect to here this capacitor that is called a bridge rectifier and we now have what is called full wave rectification so as i showed you get twice as many positive and negative pulses basically let's connect this up again now just make sure it's working then we'll put our load on again and let's see what happens so we'll switch it on i'll put my black lead to ground we now power it on what do we have we have still have -12 and on this one we still have plus 12. i've reattached the load resistors let's just make sure again we have a good connection so this is 120 ohms and this one is 120 ohms let's pose up again now and see if we actually have 12 volts coming out of it now honestly don't know the answer guys i've not tried it this is the first time let's see well first of all we better move on to volts range i mean that's the first thing what we got 12 volts yeah 12 volts so that's now giving us a stable 12 volts 200 milliamps let's go up again so let's put another pair of resistors on let's get 200 milliamps out of it again i've gone with what i had lying around so i found another 100 ohm and another 22 and i put it in power with that one so we now basically have 66 ohms so this will we also have some dodgy soldering let's just fix that one okay all right it's on there not brilliantly on there so we can connect this and i have another one the same we can now check and we should have about 66 ohms which will give us twice the current we don't need to really work it out we know 120 gave us 100 milliamps so half of that will give us twice the current yeah i mean you can do the math if you want homes or but you'll soon realize that's how it works so that's there again we will just check to make sure we have a good connection and then let's see if this can supply plus or minus 12 volts at 200 milliamps ohms ground 63 67 it's close enough it's close enough because the dc volts we'll switch it on again and let's see if it'll handle the current okay so power's on what we got 11.38 10.9 so it can handle somewhere between 100 and 200 that's what it can handle and the reason is the transformer i actually wanted to build this for my milli oh meter project the one i published on here that needs 120 milliamps on the positive supply and 20 on the negative this is probably good enough for that but we have a couple more of these transformers in these battery chargers so let's have a quick look at those as well here's one of the other charges this one only has the double a and aaa batteries it's not really very large this transformers more than the other one and this will have lower voltages it doesn't charge the pp3 than 9 volt batteries so that one isn't really of any particular use to us this is a little uh you've got the pcb out and it's stuck in there little uh surface mount pcb i wonder if we can see what the chip is on this one seems even scraping off all the other ones let's have a quick look yeah this one's a cd4060b this is like the one i repaired that originally got me interested in these charges this is a little counter so basically the way this works is it just uses resistors to limit the current into the batteries this has a low frequency oscillator that counts up 12 to 14 hours and then turns the output off that's all it does it's very very simple so it just switches off the charge current to the batteries after 12 to 14 hours time and the current charging the batteries is purely limited by passing through resistors nothing more technical than that and this is the other one so this is quite interesting it has a light bulb which i've got a feeling is effectively being used as a current limiter rather than just lighting up it has no active components at all as i can see just diodes on this side it has resistor and just all the resistors on this side some resistors here which appear and these ones also appear to be switched by this switch some more resistance here so that literally appears to be just a passive charge it doesn't seem to have any timer to turn this off or anything like that this one has the pp3 batteries which were here or while the holders were here and we have four diodes in so i think this is getting that similar to a bridge rectifier now if you look at the transformer on this there's four connections and i think this probably has two secondaries yeah one secondary here and one secondary here one i think is probably higher voltage than the other one so one will be the low voltage secondary for these batteries and will be the higher voltage for the pp3 batteries and we can figure this out if we sold our weed with a couple of wires onto here so we put a bit of power into it we can measure they see the voltage coming out of our transformer and that'll give us an idea whether we can actually use this to transform it in one of our little power supply projects i've attached the high voltage wires again this is safe as long as you understand the danger and what you are working on when i say it's safe it's it's not so dangerous as you would think but depending on your own comfort level and how familiar you are you could just put a bit of tape over the connections coming in if you were a little bit concerned about them and then you have a little bit more safety just be careful if you do this that the wires don't stick through the tape yeah you could say that so in fact it might be more dangerous to do this because you are now relying on it personally i would rather rely on my own knowledge and experience and understanding okay but if you prefer there you go so we can pull this one in now we have two secondaries one here and one here and they don't appear to be connected together it's not like a center tapped winding so let's see if this is of any use to us it may be both the same voltage but i doubt it okay power is on volts and we want ac yeah let's put this one in and see what we have okay what's coming out of our transformer well that's 6.8 volts on it yeah and that's 21 volts on it so this could be an interesting thing you won't get a plus or minus volt supply out of it i don't think i'm sure you won't because i've now switched it off and we can just check i'm fairly sure we'll find these two windings or separate in any way they're different voltages that's reading quite a way of resisting so we can probably deliver the reasonable amount of current and this one's reading very high resistance it's like the other one the other one was reading about 9 ohms so it looks like this is providing a higher voltage but there's all lower current remember that the current that's flowing through your power supply is also flowing through the transformer winding so that in itself should limit the amount of current the transformer can actually supply so really out of the three that i bought only one of them was suitable to make a symmetrical plus and minor supply and that's a fairly low power one but i think it's useful enough for little op amp based projects things like the million meter i'm sure quite happily run from that this one i think i'll actually use it as a battery charger well if you made it this far i hope you enjoyed that if you're a beginner i hope you've learned some things here if you're more experienced yeah maybe you've learned something there's nothing overly complicated in this but this is a good way to start learning electronics repair with basics like this if you get that into your head i was explaining to you about load impedance and source impedance you will get a long way with a lot of repairs i hope you enjoyed it regardless of your experience level and i hope i'll see you all soon on another world of choice repair video ciao for now guys

Channel: Learn Electronics Repair

Views: 73,334

Keywords: learn electronic repair, electronic repair, school, lessons, course, training, free, laptop repair, troubleshooting, fault finding, fault diagnosis, component level repair, dead laptop, no boot, no power, laptop, hdmi repair

Id: 1pAOBPmC7Fw

Length: 98min 42sec (5922 seconds)

Published: Fri Sep 16 2022