Fix A Power Supply! Diagnosis Repair And Restoration.

hi everyone and welcome to another episode of mr carlson's lab today on the bench is a power supply that has failed let's do some diagnosis and let's fix this power supply let's make it work again just like everything that hits the bench at mr carlson's lab let's get started this is the power supply that we together are going to diagnose and repair now i've owned this power supply for many years and i haven't had a single problem with it the thing has worked flawless so aside from me sliding the insides out of the case to mount this below those two very large oscilloscopes i haven't been beyond that and when i say i haven't been beyond that inside this thing is a large black heat sink with a bunch of past transistors so i've never removed that and actually been into the power supply so we'll discover what's underneath that black heat sink together so i'm kind of excited to see how this thing actually is put together now it's been a really great power supply and i use this all the time now since this is normally below those two oscilloscopes i've mounted this above my microscope there and whenever i'm working on a project under the microscope that needs to get powered up i use this and since i'm designing a new piece of test equipment on patreon that i'm going to be releasing here quite shortly i'm working under that microscope a lot lately and i turned the switch on and absolutely nothing happened and i'm very surprised because when i shut the thing off the last time everything was just fine so i really don't know what happened between then and the next time i turned the thing on very odd so i'll give you an example of what's going on here so it's not plugged in right now i'll just plug this into my isolation transformer and current limited variax apply i'll turn that on turn the switch on and as you can see the light comes on but nothing happens so this usually indicates that the primary of the transformers is you know getting ac now if i move the voltage adjustments around this would normally move right this is nothing there and on this side same thing now this is another thing that really bothers me that i'd like to address in this powers playing it's bothered me since i've you know owned this thing right from the beginning so let's give you an example all right so turn this down as you can see it's ridiculous okay so now say i'm at 0 volts and i need to get to 25 volts really that's 25 volts now so i can do that with a single turn potentiometer so i can get you know a couple zeros out of it so if i want 5.00 volts i can do that with a single turn very easily i don't need to have 10 turns to do that i guess if you're fumbling around and you want to quickly get to you know two zeros or whatever by doing that you know i can sit there and just do that and then i'm at two zeros it's just that easy so i want to get rid of those things it's just it's drives me crazy these two things uh the current won't display anything unless there's current being drawn and this is the current limit so this sets the current limit so that's that is a single turn that's nice so what's very interesting about this power supply and this is part of the diagnosis procedure already now again i haven't been below that heat sink or anything i haven't done anything at this point you know as much as i do we'll discover this all together and that's kind of the fun of this whole thing so now when the power is on i can hear the the power transformers turn on now this is a linear power supply this is not a switching type power supply it's really heavy it's got two big transformers in the back and i don't think you can hear this but i'll i'll try anyways when i click the switch on you'll hear the transformers hum for a moment and then settle off so they go um when i first turn the thing on all right so let's see if you can hear it all right i'll do it one more time let it sit for a second all right i'll turn it on again so when i first turn it on it goes um so that indicates to me that there is obviously current getting to the primary of the transformers inside this thing but nothing is happening here now the reason that when you first turn this thing on well it could be a couple of things you're not turning the thing on and zero cross or it could be charging a bunch of filter capacitors inside this thing and that is most likely what's happening because every time i click this it does that so yeah there it is again that was very pronounced right there so that was probably empty filter capacitors and turning this thing on at the peak of the ac cycle at any rate that tells me that the primary of both of the transformers in this thing are receiving ac and there's a really good chance that those transformers are charging some filter capacitors one two however many is in this thing it'll be charging them up all right so that already tells me i've already diagnosed a bunch of this thing without even having to remove this thing from the case that's just from listening and you know looking at the signs now if i was to click this on and this lamp didn't come on of course immediately i would suspect a fuse or something like that but the fact that i can turn the thing on and nothing happens on either side is very interesting maybe both sides are controlled by one particular area and this thing as i say i don't know we'll open this thing up and find out what's going on here in just a moment so at any rate i need this thing to work and i need to use this because i'm designing that new piece of test equipment and i was relying on this thing and it just stopped so let's make this thing work so one of the nice things about this power supply and the engineers that put this thing together and you know i do give them a hand is it's uh extremely difficult to get into the case of this thing i'm being silly there's one screw that's it you remove one screw and the whole thing comes apart slide the whole thing out that's good design you know it's a nice the case is nice and tight it's held together very well and all you need to do is remove one single screw and the whole thing comes apart that's great now beyond that inside there's obviously going to be more screws holding that heat sink on and everything like that but we'll address that when we get inside this thing so what i'll do is i'll reposition the camera above this thing i'll slide this thing out of the case let's take this thing apart and start fixing this thing let's make it work again because i really like this power supply it's a great power supply get it done looks nice with those meters in the front and everything isn't that a nice looking supply all right let's make it work all right let's open this thing up and see what's inside okay so nice soft mat here tip this up like so and hopefully there's enough room between this and the camera i'll move that up get that out of the way of course the unit is unplugged while i'm doing this all right just move this around get this line cord out of here line cord comfortably slips through that little hole there okay so there's the top side the usual dust and stuff on here all right so looks like this is a smaller phillips these ones here i'll remove kind of the plastic is yellowing definitely an older supply been very good to me grab this this one the right one it is now one word of caution of course you want to make sure that this is unplugged from the wall and as you can see i'm putting this in here i don't want to accidentally touch this to a pass element because usually the cases of these things the collector of this it says on their 2nd 3055 which is probably one of the most common transistors on the planet at any rate i wouldn't want to touch this you know come close to that and touch that because if there is a large filter can charged up inside this thing really bad things could happen i'll just create a lot more work for myself if i do that so just keep that away from there and go over to this side over here so you got to remember in these linear power supplies there's usually large capacitors inside that do the filtering now two amps isn't a whole lot of currents gonna be crazy big but still big enough so you can't have to move this off to the front so i'll just move this over like this i don't looks like this is gonna come very close to those meters i don't wanna scrape those meters and it sits right below it okay good that's what's inside this wow that's actually really nicely put together kind of a nice surprise usually this older stuff is very well designed and this is no exception these nice big transformers in here and the filter caps so a very quick shortcut here usually when they socket things those are the suspect issues okay so the reason that they socket those things is for a reason and of course the pass elements on the top are socketed as well now whenever any type of linear power supply you know is is bad the first thing is obviously check the fuse and then of course pass elements are the suspects now unfortunately usually when a pass element fails there's a reason that these are socketed as well because they usually take out the little ic now this is an ic that i have not seen in a very long time this is an mc so motorola 1466l so mc1466l date code on the bottom 77. and this one here says 74. so very old ceramic type ics and these things are no longer available and they are not a very common part in fact they're getting very difficult to find so i haven't seen an mc1466l in a long time and the fact that it's ceramic too very nice you know they're very nice ics so hopefully those aren't bad hopefully both sides aren't working and as i say i just turned the switch on and nothing happened and i'm telling you i turned the switch off the last time turned it on the next and there's just nothing there which is odd because there's two power supplies and both sides aren't working which is really odd to me so i don't know i'm thinking maybe some a really bad static discharge or something maybe in here i have really no idea at this point at any rate so the first thing that i want to do is i want to make sure that the you know the capacitors are discharged and how i'm going to do that is i'm going to turn this thing on its side or maybe even upside down and as you can see on the bottom there's a bunch of screws and those two screws are gonna be what i wanna test so what i'm going to do is i'm going to go get a meter i'll get a meter in the shot here and we'll make sure that those caps are discharged properly right back i have my capacitor discharge device here and what this will do is this will indicate to me when the capacitor is discharged so this box will safely discharge those capacitors and i'll be able to see when the charge on the capacitor is you know basically gone now i've added provisions to add an external meter as well so if i actually want to watch that fall on an external meter i can do that but i'm just going to rely on these leds right now to see if these are actually charged up so here we go and there's nothing there no everything looks like it's safely discharged and here's that other capacitor nope so there is no charge on those capacitors at all so i'm okay so this is another thing that i've released on patreon if you're interested in the capacitor discharge device so i use that all the time for working on vacuum tube equipment and this stuff as well and it allows me to safely discharge these without any big sparks and without hurting anything okay so what that tells me now is that i want to be testing these pass elements so both sides are toast so you know like when i say toast i mean not working so both sides let's put this like so like this and there is no charge so what's nice about these is i can just very quickly remove a pass element and test it so what i'll do is i'll grab a screwdriver here and i'll just remove one side now both sides aren't working so if i remove one side and these are okay then that's in there pretty tight there we go they could have been a little bit uh a little bit more thorough with that compound let's move that over here not very much heatsink compound on the bottom of these things so at any rate i'm going to go get a tester here and i will just beep this out with a normal tester so give me one second here and i'll be right back i'll grab a tester this is the npn pass element off the top side of the heatsink there so this is a 2n3055 npn transistor so in order to identify the leads it's very easy so if you can remember the leads that are closer to the far end so if you have the transistor sitting on the bench in front of you and these leads are closer to this end so they've set the leads off closer to one end so that this is indexed so it'll only go in one way right so if you can remember when the leads are closer to the far end this is the base base emitter and collector so this lead is the base this lead is the emitter this is the collector and this is an npn transistor now you can also memorize it the opposite way around some transistors actually have it written this way and others you know don't have any writing on them like these ones here right so so we can test this very simply with just a simple little tester that i've built and i'll also show you how to test this with a standard dmm here in just a moment so if this tests okay this will be blue red and blue so blue being n and red being p okay so n p n so blue red blue if it was pnp it'd be the other way around red blue red so let's just connect this up here and i'll show you how to test this with just a standard dmm in just a moment okay so we'll go emitter and i'll go collector and base so if i get two colors glowing at the same time like a purplish looking color there's a short if it's just red blue and red or blue red and blue it's okay right depending on whether it's an npn or pnp transistor and there we have it n p n and it's okay so again if this was shorted so if you saw something like this it kind of blows out on the camera a little bit here i'll just hold that against here and put my hand over it so you can see see how it's kind of a purplish kind of pinkish kind of color that's because both the blue and the red are glowing at the same time that means that it's shorted okay so this transistor is fine again as you can see blue red and blue right npn no problems nice thing about this is also detect leakage in transistors very easily as well and i can display that with the other transistor here in just a moment so i'll get this out of the way and i'll show you how to test this with just a standard dmm as well i have a dedicated video here on youtube about that it's one of my earlier videos i'm up against the white board doing that put this on here and here and here like so so if you have a meter with a diode test on it just like this get this more into focus here you'll get a beep or you'll get a solid tone if it's shorted or you'll get a beep if it's just a standard diode so since this is an npn transistor we want to put the red lead which is a positive on the base and we should get two diodes so i should get a diode if i touch the collector and i should also get a diode if i touch the emitter if i get a solid tone then it shorted okay so this should test as two diodes so i'll hold this onto the base so i should get a beep and there's a diode no problems and i'll do this here and a beep so there's no problems with this transistor so this is to the emitter right here see this right here and this is to the collector no problems again if something was wrong uh yeah i would just get something that sounds like this all right so if it shorted it would show that okay so now what i'll do is i'll remove that other pass element and that's off to the side here all right so this is a darlington type transistor so there's actually two transistors in here in this one case and there'll be some resistors in here as well how do i know this well i'm working on power supplies for a long time okay so let's see if this meter detects the resistors inside this probably won't okay so on all right so let's see it should test as a diode and it does and we'll test this and no problems you really can't see that leakage inside here's a little high you have to be really familiar with your meter to recognize something like that so this is a darlington a darlington transistor and there's also resistors inside here and this is not going to show us anything like that this meter won't if we were to put this on a curved trace or something like that we'd definitely see that so let's see if a little other my little tester detects those things so let's put this on here so let's go emitter and collector and base and yes it is detecting it i don't know if you can see that on camera two colors are glowing here the red and the blue are glowing and this is a little bit of blue in here so this is more of a pinkish kind of red color i don't know if i can bump that down let's see if i can get that into the focus here will it focus on that you can just see on my end it's very noticeable but you can actually see the little red emitter going in there and this one here has the blue and the red glowing as well but a little bit harder to see very little blue glowing it's up in that little corner there so this is actually seeing the leakage i don't know if i can get anything better with that let's see now it's hard to see on camera because it's so bright right sure be nice if i could just display that for you but again it's just so incredibly oh there you can see them see a little blue one glowing up in the corner and a little red one glowing in there so on my end that's very noticeable but on camera it just washes out so this is actually detecting the leakage whereas the other meter didn't see it so there you have it one passed there we go so there it is so this is okay and it's actually seeing the resistors as well so this is another project that's available on patreon if you're wanting to build something like this there's nothing special about this it's all off-the-shelf parts you can go to any of your local parts supplier and get the parts for this and all the plans to make your own circuit board and everything and the layout is all size and everything up there if you want to put something like this together for yourself i use the thing all the time where i really find this thing useful is you can see this down here there's an sot-23 pad and a lot of the times i'm working with surface mount stuff i'm just touching the leads together here i'm working with surface mount stuff so if i pull a bunch of them off a reel and i have a you know a selection of pnp and npn and all those on i can just slide them over and identify them and if any of them are faulty if i want to check one i can just slide it over and test it out on here it'll also test you can just plug in the 2sa 2sb to a c2sd series or the 2n series in here and test them out and all that kind of stuff so a neat little tester to have i use this thing all the time in fact i used it earlier today a whole bunch all right so so far we know that these are okay what does that tell us so far not very good things because we're getting closer and closer to that obsolete ic and it's really starting to look like that obsolete ic is bad now again i just turned this thing on and if the outputs were shorted or something really went bad these things would just go away so we're getting close to a part that's you know really deep into the power supply that's gone faulty it's looking well at least it's looking like that at this point not good all right well i'll just put these things back in the on top of the power supply and tighten them back down and we'll start looking for other problems i'm going to put both of these pass elements back on just the way they are i'm not going to put any thermal compound on this right now because who knows i might be taking this thing apart again later on so in the end i'm going to put thermal clean these off maybe i'll even replace these and put new thermal compound on here and again i'm going to put a lot of it on there i'm not going to be skimpy with it now again you know you're using common sense right you're not going to put a thick layer on it so that it's squeezing down into these holes and then when you tighten this down you this big drippy mess inside you're using common sense but you can spread a nice decent amount of this stuff on on both sides of this so again you don't have to be too sparing again using common sense right you're not gonna make the thing swim in it or something like that but you definitely go easy on it the nice thing about these sockets here is that you know you can just take transistors out and test them now since this is a coarse threaded screw you have to be kind of careful if you're going to put these things back in and you find that it gets tight in one spot or something like that back it out and then try again because chances are it's not threading in properly so there we go and i will put the driver back on just like so you just wiggle them around like this until they find the little the pins find the little i guess you could say their other meeting side so the little socket just wiggle it a little bit until it pops into the socket so that um it mates properly with the socket don't be forcing them down or trying to bend the pins or anything like that right put this on and like so now you don't need to cinch these things down to the point where you're going to be you know snapping the screws off but just nice and tight so you just want them nice and tight and of course when you put new thermal compound on when you tighten them down you're going to get a whole bunch of it squeezing out and of course some of it is going to squeeze into those holes where the pins are as well so what you want to do when you put the stuff on is when you put the transistor in usually those pins don't have any thermal compound on them and they're absolutely fine if you find that there is when you smear it on the bottom side of the transistor and you have the mica spacer on here and things like that you want to make sure that the pins of the transistor are clean try and get as much of that thermal compound off the base in the emitter pins before you slide them into the socket if not you're going to have thermal compound in the socket as well this is some things to keep in mind right again a bunch of it's going to squeeze down into that hole where the pin goes that's that's fine if a little bit goes down in there as long as the pins themself are clean when they go through that's a that's just a good practice you don't want the thermal compound all over the emitter and the base leads now i've seen you know these absolutely smeared with that stuff to the point to where it's dripped down inside the chassis of course that's not using common sense right you're not going to be doing that but it's never really affected the power supplies at all i've never seen it affect any type of power supply having that thermal compound actually you know on the connections here or anything like that but it's just good practice to keep that about as clean as possible so at this point we're getting closer and closer to this thing right here so let's start going inside here and testing some things so i'm going to see verify that there actually is voltage and you know we have voltages on the different parts of the board and we'll work our way towards this little ceramic ic here this is what's inside that mc1466l this little ic right here so looking at this diagram pin 14 is the supply for this ic and pin 7 is the ground and then we also in the internal voltage regulator area we also have from the cathode side of the zener diode a line that runs over to pin nine so that'll be a bit of a clue in the testing of this without this ic in there at any rate we'll worry about that later so let's test to see if there's any supply voltage from pin 14 to pin 7 here so i'll just put this in here [Music] put that on to dc so i have some sharp probes here let's move this out of the way and zoom on in a bit so we can see this a little easier so what i want to do is turn the power on and test from pin 14 which is positive right here to pin 7 which is negative so turn this on i'm going to attempt to do this on camera so i've got to be very careful so these sharp probes here are insulated right to the tip so if i slip i'm not going to shorten any pins so let's see here that should be pin 7 and pin 14. look at that 25 volts looking good so if we also take a look at this pin 7 here is ground what drives the pass elements is pin number five here so that's the output to the pass element so we want to see what's at pin five so pin five to pin seven so we'll go back here to pin seven again being very careful and we'll go to pin five which is right here and there's a little over half a volt on that and the vr on the face is turned right to the maximum so it's definitely faulty and i imagine it's going to be the exact same for the other side i'll just quickly test the supply voltage here there it is twenty five point whatever four seven four eight volts there's the leads right on top of the meter i'll show you that again there it is so these ics are definitely faulty that is really unfortunate the power supply is off it's unplugged and the caps are discharged and at this point i am just going to set up something so i found a 10k vr here and i'll probably use something like this to replace this 10 turn thing over here in the end at any rate so what i want to do is i just want to remove the ic and plug this into the socket here so what i'm going to do is i have my soldering iron warmed up so i'll get rid of this wire here and i'll put this so i just want to put this on the wiper just to limit currents this is just a 4.7 k ohm resistor again this is going to be driving a darlington transistor so there's definitely going to be enough current there to turn the whole system on add a little bit more solder here a little bit of solder our little friend here which is 4.7 k ohms he's just gonna be here to protect the vr from anything bad happening just in case something bad does happen and then i also want to attach a 100 ohm resistor let's see uh would that be yeah that'll be okay i'll put it on this lead here it doesn't really matter which end i put it on so i can bridge pin seven to what was it pin nine on there that's right so i'm trying to get this all into the go out here so you can see what i'm doing so this one here i'm just tacking a bunch of leads together is all i'm doing right now just so it stays there just so we can quickly test this thing and see what happens okay so now what i want to do is remove this ic it's been in there for ever a little bit hard to get out there it is lift them up nice and straight so i don't bend the pins that came out nice so put this little fell off to the side here so you have pin 7 to pin 14. so pin 7 is ground so i want to use one end of the vr to ground so we'll go pin seven and we'll go to pin nine right because we want a 100 ohm resistor to pin nine just for protection so the wiper will go to where the output is so that would drive the pass elements which was pin five yes it was it was pin five this would be pin four this would be pin five and then we would want this one to go to 14. that goes in there there it is just make sure that's turned towards the ground and this is the ground end okay so let's see what happens see if we can get anything to happen on this thing so prop this up so you can see the meter so we're going to obviously be on this meter here and i will put a roll of solder or two under here so we can see this in real time okay so there's i don't want to wash that out so there we go so there is the meter i'll just move this over here so that we can get a good look on that so there's the meter all right are you ready let's see what happens here we go power on there it is so what does that tell us you can see see if i could move very very fast i could be the regulator but that would be extremely fast i'd have to have reflexes like bruce lee in order to do something like that all right so what does that tell us tells us that both of these are toast very interesting so what i'll do is i will just shut everything off here you can see obviously there's no regulation any type of line voltage movement in that needle is moving see that and that's just bobbing around there that's my soldering iron at the other end of the bench turning on and off right it's regulating the temperature of the iron you can even see the movement of the needle just by the iron going on and off so as you can see obviously no regulation whatsoever because the ic's out of there but that's the way that you can test these things to find that out so basically just putting a vr in there all right i'll shut that off all right get this out of the way and i imagine it's going to be the same for the other side i could do the same for the other side but it's just at this point it's looking pretty much like it well you know what why don't we just check it out at any rate so what i'll do is i will just take a quick measurement here and see if the other side is discharged see if this is all discharged because i don't want to be doing that anything here while there's anything happening all right let's go across this cap no it is not discharged that is definitely not discharged it's going down slow let's look at the cap discharger in here [Music] zoom on out for a sec i think it's discharging slowly as i'm actually just moving things around here i'll keep an eye on this here get rid of any residual charge yeah there you go now the pass element make sure that there's this big can here is discharged pass elements are going to be attached to the larger supply so i'm going to stick the probe into the negative lead because that's going to be part of the supply and i'll just make sure that there's nothing on these collectors nope so all the pass elements are going to be okay they're going to be i mean the capacitors that are attached to the pass elements are going to be discharged see this one here is discharged oh that one still had a charge on it as well i can get rid of that all right safely discharged that out of the way move that out of here stick my hands in here and get this thing out okay another one out let's get this guy out of the way unplug our test jig so we go from pin seven to nine this one should go to pin five all right let's check out this side have a feeling it's going to be absolutely the same so this time oops put this here like so that doesn't slip again keep an eye on this turn that right down there it is so yes both of those ics are toast since both of these ics are faulty and they're getting very hard to come by nowadays and these capacitors are going to need changing this one here most likely too i'm thinking that i want to make something that i can service down the road because i really like this power supply so you know what i think i might actually just design a new board and replace this so what i'm going to do is i'm going to take off all of these connectors they should just pop off like so so i'll remove all of these wires and connectors and take this board out and we'll take a closer look at this board and i'll talk a little bit about my thought process as i'm going to go about redesigning this and putting a completely different board in here with a different type of regulator i see and everything here's the regulator board out of the power supply and it really came out quite easy so this is just basically pushed down onto some plastic standoffs so you just kind of go click click and it just pops off like that and then you just pull little wires off of these connections here and the whole board comes right out so it's very easily serviceable so way back in the day when the power supply was closer to being new than it is now you could have probably called up anatech if you had any problems and they just ship you out a new board or maybe just even an ic or whatever you need and you could have your power supply up and running in no time now since the components on this board are outdated and hard to find what i'm going to do is just redesign another board and fit it in there with components that i can find that are readily available so i want to make sure that my board fits into the exact same spot that this one came out of so i need to make sure that the measurements between the holes are exact and i also want to make sure that the board is exactly the same size i want to reuse these connections here all of these connections here so i got to remove these from this board and i'm going to install these into my board and i want all the remaining wires that are in the power supply to attach to the same area that they attach to on this board so basically my board is just a direct replacement it plugs right in maybe with only some minor modification something like that now usually these capacitors here made in canada usually these capacitors are very good even to this day so what i'm going to do is do a thorough test on this capacitor and if it is still good i'm going to reuse this in my design be kind of neat to have that in there because it'll look something like the original board but again it'll be quite different with modern components because it'll be completely different design so i have a lot of measuring to do i'll get started on that and when i have some results i will be back all right i've taken a whole bunch of measurements here and i've also mapped out where all the pins go on the board so i can reconnect the same wires and of course design my new supply to fit in place of this existing board tested the capacitor the capacitor tests extremely well so i will reuse that capacitor so you can see here we have the power transformer down here and it attaches to this area of the board right here so the two red leads which is one winding out of the power transformer runs just over to the mc1466l all right and then we have the green a green yellow and a green so the ends of this winding here attach right to here and what they've done in this is they're running a full wave bridge rectifier here and then the center tap is rectified as well the center tap of course is half of what the end to end voltage voltages so if we have you know 44 volts we're going to have 22 here right so we have 22 volts at this point right here running to the collector of the 2n3055 right so this is the one that connects to the post on the front here this is a 25 volt regulated power supply under load that'll drop to about 20 or some odd volts so the mj 1000 which is just behind it which is driving this is doing some of the work as well because there's 40 some odd volts on the collector of this transistor very interesting design so of course when i design my supply i have to design this you know whole idea into that as well so this runs off to the current limit over here and then of course we have the black and the whites of the black is the negative lead and the white is the positive that runs out to the current meter and then out to the post then of course the voltmeter is just across those posts and this here is what sets the voltage voltage set over here pretty straightforward so i'm on my way to starting the design here so of course i've measured up everything so the new board will just pop right down in and the capacitor is the way that they've mounted this is kind of on a bit of an angle as you can see that so i'll just have this straight like this on my design a little bit easier don't need to have it mounted like that so lots of things to think about so away i go i'll start designing a board and i will be back soon with some ics i'm going to design this board with some ics that are readily available or at least something that i have right now i ended up using a few components off the old board so i used that main filter capacitor and two resistors aside from the little pins or the connections that i've removed from the board now believe it or not removing those connections from this board was a real big pain one of the biggest pains of actually doing this entire project what they had done is they pushed the pin through on the top side and on the bottom they open it up so they kind of crimp it or i guess you could say part the metal on the bottom and they've soldered it after that so i'd have to de-solder it really really well and then where they've crimped it i had to pinch it all back together again so basically fold it together and then pull the pin out of the top side of the board so a lot of work because that's a lot of pins and then after that i had to clean the pins up and then put them into the new circuit board which is right here so this is the newly designed board that will be on one side there'll be two of these inside that unit so at this point i just have this one done so this is pretty much the same thing it does pretty much the same as this board right here the difference is is instead of having one ic like this one this one has two ics and the ics that i chose for this are the ua 723 so i'll zoom on into this here and i can take a closer look so these are the two resistors that i've taken off the other board as you can see on this board i've soldered the pins on the top side as well as the bottom side so this is very sturdy now whereas on the old board it was just the bottom side that they were soldered in right so that is all done so this here is the current adjustment so i can set the maximum amount of current right here and on the bottom side is pretty much the business end of things here so there's two ua 723 ics here and these are readily available unlike the lm 723 now so these are still available and i have quite a few of them so if anything ever does go wrong with this i can very easily just replace those ics so the reason that there's two is one is a negative five volt supply here so you can look at this little area right here like the mini version of this entire power supply so this is the pass transistor right here and this ua 723 controls this this adjusts the negative 5 volts the reason i need negative 5 volts is because this ic here is doing what the original ic on this board did right here now the ua 723 will not go down right to zero volts so in order to make this go right down to zero volts or very close to i need to create a stable negative five volt supply for this so that i can bring it down that low so this is the negative five volt supply set and this is the zero set for this side and i'll have to adjust all of that once that's inside that power supply so the way i've designed this is you know there's a little border cut out on the bottom all the adjustments are very easy to get at on the bottom i don't really need to worry about that so the diodes that you see on here these large diodes on the top are surface mount diodes right here so these are 100 volt 6 amp surface mount diodes right here see what else can i tell you is another one here that's from that center tap there's a bunch of shot keys to stop things from going negative so there's a bunch of hitches whenever you design something new like this so when i say going negative what happens is because this has two separate regulators in here this negative five volt supply has to stay at negative five volts while the main power supply capacitor discharges and that is discharged by this resistor right here so as soon as the power is shut off this resistor right here is discharging this capacitor immediately the reason that these two capacitors are so large over here so you can see 3 300 micro farad at 35 volts is to keep this supply up the negative 5 volt supply while the other one discharges if not what what'll end up happening with the supply is as the if this goes away first or goes away quicker what ends up happening is the power supply will actually go down a bit and then it'll raise in voltage again as it and then it'll slowly come back down so everything needs to be kept stable so now this also is another capacitor here which also is with a zener diode you can see this little zener diode here so this is regulated here as well and then that runs into this ic so that also has to keep everything nice and stable so there's a lot of things going on on here so quite a bit of planning and design work so this little diode here is there's a little diode under here with a heat sink on top of it and i designed an area a whole bunch of i guess you could say a lot of copper area here for this to act as a heat sink so this diode is in series with these current shunt resistors really is what these things are so our current sense resistors i should call them so what ends up happening here is because the way the ic works in this circuit there isn't enough drop across this to properly operate the the you know the current sense section in this right there's a current sense transistor inside the ua 723 and of course the transistor needs 0.6 of a volt to turn it on right so what happens is since this diode here is in series with these resistors here it allows me to establish that 0.6 of a volt plus and i can adjust it with this here so that i can get that variable current control on the front of the unit so that's how that all has happened on here what else can i tell you about this thing that's you know pretty much what's going on here in a nutshell i could you know really get into the specifics of this but i'd be talking for a long time so now to put this thing inside the power supply and change that variable resistor on one side that 10 turn variable resistors drives me nuts so anyways i'll get rid of that thing put a single you know one turn or whatever like it would be just about one turn uh you know variable resistor in there and put this in and we'll try it out see how well the thing works i have the new regulator board installed and it fit in just perfectly so lots of time and measurement paid off all the wires are all in place everything is ready to test i also changed that variable resistor so it's pretty much ready to go now whenever i design anything i design around center values so what i mean is when i put the vrs and you can see this is pretty much in the center all the vrs should be sitting very close to their center position that's the way they come out of the package right so they should be sitting very close to their center positions and i should have very close to negative five volts i should also have very close to zero volts on the on the meter here and this should be sitting somewhere around two amps should be current limiting somewhere around that so it should come in close so what i'm going to do is i'm just going to prop this thing up and i'll secure this so that it doesn't move around i don't want to short anything out and damage this board and then have to go about fixing this so i'll just make sure everything is you know nice and sturdy i'll prop this thing up and we'll take a look at it i'll turn it on and we'll check out its functions the first thing i want to do is check the negative 5 volt supply and see how close that is so i'll turn this on i have the meter attached to the ground post on the front just with an alligator clip and i want to see if this is at 5 volts and if not i'm going to adjust this again so negative 5 volts so i'll turn this on and i'll come in here with my sharp probe touch the test point that's pretty close 5.02 so i think this end here has got the sharper of the two that's this one here so i'll just move this in here like so all right five volts right there so that's set now the next thing i want to do is check the zero so i'll put this in here i'm at 0.74 oh that's so close i don't even think i need to worry about that so if i adjust the zero again one of the ends in this thing is sharper so i like using that end and i'm going negative now so you can see i can adjust the zero way up right 0.3 of a volt 0.2 0.1 and that's zero volts right there so that's set so now that that is all set i'll move this i'll stand this up and we can take a look at the meter on the face and we'll load it and we'll see how well this deals with the load all right let's try out the power supply so i'll turn this on i must not have the sitting rated zero must have bumped that there we go so zero now keep in mind that these meters are not going to be completely accurate because the power supply is sitting on an angle it's propped up by three rolls of solder here so we can see this in the camera in order for the meters to read completely accurate this needs to be sitting on a flat surface it's very common for you know meters like this to to be like that so i know before the power supply failed these meters were very accurate so i'm pretty confident in that so i'll turn this up look at how smooth that is very nice very happy with that much nicer than that 10 turn it's very easy to dial and look at that if i want 15 volts it's 15 volts if i want 10 there's 10 right there if i want 5 there's five so on so it's very nice so now what i need to do is i need to set up the current limit so the meter it ends at two amps but i really want this to supply about 2.2 amps because this is a really soft current limiting action in this thing so what i'm going to do here is turn this right down i have a 5 ohm resistor here okay big 5 ohm resistor so i'll just use that as the load it's very accurate it is right at 5 ohms and what i'm going to do is turn this up to 5 volts so 5 volts into 5 ohms should give us 1 amp so i'll turn this up and that's really close to one amp right there pretty much sitting right on the 5 and as you can see it's really close again a little bit of inaccuracy because this is on an angle so not too bad so if i turn this up to 10 volts into 5 ohms we should have 2 amps and it's very close so now if i turn this up you can see this is going way over so that should be current limiting out at about 2.2 amps all right and i'm sure this will go much much higher so what i'm going to do is i'll very carefully put my screwdriver into this vr here and i want to turn this up and i want to bring this back down to about turn that way up i'll bring that to about 2.2 amps so this is right at the end so if i was to remove this cable it'd go right up to about 27 volts so about 2.2 boy that's a right there close enough all right so i can turn that down so you go to yeah that's looking really good lots of cables and loss and stuff like that happening here so it's close enough that's very very close now what i want to do is i want to see if this is going to current limit correctly so say i've got one amp happening okay i want to turn this down i can turn that down to say 0.5 of an amp or even lower you can see that so i'll bring this rate up to about 2 amps you can see that i can current limit this out so it'll top out at about 2.2 right bring it down to supply 1.5 amps right there or 1 amp 0.5 of an amp right down so that's working very well i'm very happy with the results oh yeah i should demonstrate the regulation how well this regulates so i'll turn this up to about five volts somewhere in there just like this now i'll add one amp worth of load here and as you can see the voltmeter doesn't even move bring this up to about eight volts now this will start the current limit out at about 10 volts so it's that soft current limiting action so it should hold pretty solid rated about 8. as you can see just still rock solid and when i bring this right up to 10 volts so i'm going to be right at about 2 amps it's going to start to soft current limit you'll see just a little bit of movement in the needle in fact i'll bring it just a touch above so here we go there you go just a little bit of movement hardly anything at all so it's working very well now of course i could make this completely solid by upping that vr inside again but i want that soft limit in there now the fun begins i have to build another one all over again for the other side uh that's a lot of time into this thing but at any rate i hope you enjoyed and i'm going to talk a lot more about power supplies here very soon i have a bunch of schematics and stuff ready we're actually dealing with some power supplies and and um you know high voltage supplies and things like that on patreon right now so i'll talk a little bit more about this up there very very shortly probably within the next day or two i'll have a video up about this of course from the date that this video is produced and um you know i'll have another video on this and maybe i'll even expose the schematic and everything for this and talk a little bit about this there as well so hope you enjoyed the video and that's the power supply project done and very successful i'm very happy with that if you're enjoying my videos you can let me know by giving me a big thumbs up and hang around there'll be many more videos like this coming in the near future we'll be taking a look at vacuum tube and solid state electronic devices alike so there'll be a lot of troubleshooting repairs diagnosis and lots of restorations coming on this channel so if you haven't subscribed now would be a good time to do that as well if you want to be notified as soon as i post a new video don't forget to tap that bell symbol if you're interested in taking your electronics knowledge to the next level and learning electronics in a very different and effective way and gaining access to many of my personal inventions and designs you're going to definitely want to check out my ongoing electronics course on patreon i'll put the link just below the video's description and i'll also pin the link at the top of the comment section so if you click on the link it'll take you right there all right until next time take care bye for now

Channel: Mr Carlson's Lab

Views: 233,157

Keywords: repair power supplies, powersupply repair, Restoration videos, repair video's

Id: 37lIpTxUQcE

Length: 61min 21sec (3681 seconds)

Published: Wed Sep 16 2020