Fixing a faulty USB power supply.

I'm going to start this video by mentioning I've got a bit of a cold I went to bed feeling fine yes they woke up the morning blocked up Nords feeling terrible so my voice might sound a little bit odd but I'll just try and get by and I'll try not to sneeze on the workbench so this is our power supply that it's a USB power supply it's the new type with LCD display and it's faulting I notice a really good call to control every when it peeled off the little surf translucent film from the front there's a big speck of stuff in the screen under there as well but what's actually happening with this area it's a friend called Paul who bought it from what was a company called it was gearbest and when you plug it in I don't know if you see how it just pulses the display pulses that displays this a 5-volt display and then it just sort of dies again that keeps redoing that they typical that you actually do it for a while after it's been unplugged as well but he got it from gearbest it's faulty he tried using their online returned for him and it didn't work the capture didn't work you know tick boxes didn't work so he emailed them and they just didn't blow responding so that's not a good demonstration of their customer service from gearbest but that's the point you said screw it I'll send it to big Clive and he can we can see if he can do anything with her or at least make a video to it so here it is let's open it and see if we can make a video so it's got a little seal here to stop her just stop us getting in oh that's quite sticky that's the seal removed now is this going to smudge it apart nicely or is it just going to make splintering noises the case doesn't look super that's not very good okay so it wins points for accessibility to all the live connections here's the circuit board it's not very easily oh wait not not it's kind of pulling that that front or the front display is flexing oh okay so insiders the display circuit board how does that connect this care it's got 10 connections it's got a four pin connector there and a 6 pin connector there technically speaking if it's not really working I should really discharge what I think is the big flat capacitor I think it has fully discharged in fact I was still trying to run the circuitry but it's I see a big plaster there here is the main site the main site is coming in here we get a main screen here and it's going to reckon that's the mean electrolytic let's use a metal screwdriver to just bridge is dead that's good and the hand test yeah it's dead so what we got here then let's zoom up a little bit and we'll explore this together so we've got the mains come in here it's going to these two pins one end is going to a combo depression choke here the other end is going through a fuse under there this is where incidentally help returning it backwards and forwards when you're actually looking circuit board you tend to flip backwards and first to see what's another side versus the tracks and I watched other channels just at the point I'm saying oh what's that they'll generally flip over look like I wanted to see that bit so I my apologies if I'm doing that to you so we've got the fuse from one of the input pins we've got an NTC thermistor which air is that it looks like a black pastor but what it does is it starts the site of our resistance and when you turn the power on it heats up initially it starts the higher resistance then it drops the low resistance and it just takes off that buying the current surge when you turn it on it both those connections then go through the common wood suppression choke and then and guess yes they seem to be linked to the site it's double sided board to a suppressed capacitor here a class X capacitor filter capacitor then a bridge rectifier the bridge rectifier is then going to this electrolytic capacitor which is menacingly mounted right next oh it's glued onto which would I hire this which would ship or a transistor now that's not good that if I actually glued on to that it's commendable they've glued it down I think I'd rather put a bit of glue at the end there instead of actually on to the side because they have physically I don't know if you're going to be able to see out it's all well shrouded and let's get a bit of momentary light in there briefly they've glued on to that transistor in there that that seems a bit odd the transistor which is being driven by the ship alright life say it like so analyse the circuitry here so this is a switch would ship the look of it that's a transistor that's switching the transformer there's the primary of the transformer probably yes because it's in the there's here's a separation trail let's say draw this in here the separation trail is coming along here then it's actually cut out like that then it seems to be going up and over to there then they've got more cutouts to keep us spacing a minimum spacing here so there is a separation path between the hein low voltage side so both those connectors which is reassuring are on the low voltage side and they've made efforts in this instance to get proper separation which is reassuring not sure how good the transformer will be you never really know until you open it up so that just farmer has quite a few connections I'm guessing this is primary because it looks like this a set of components here our diode let's say get me a bit closer to that a diode three resistors in parallel with a capacitor yeah that's a snubber network so that is a the snubber across the across the primary for the switching to cut the switching transients clip that to protect the transistor so those are primary that must be the either feedback is that an opt isolator yes it is there's an opt isolator there Oh actually yeah that's a fairly sensible circuitry as well the opiate is a big cluster of capacitors it's using a big fat diode here coming from the output of the tube yeah they've got lots and lots of pins together on this to handle this of high current from the secondary side so it's going through that diode by the look of it they're good or smoothing capacitors and then there is a little feedback circuit which is probably it looks completely autonomous it looks like it's there based on one of those TL 41 type air shunt regulators with a simple resistive divider so maybe it's just absolutely setting I'm just scraping that and seeing what's there if I can get their text off that I think that it's a 4-3 one number right so there's a little bit secretary there with the matching resistors and capacitor which would set the threshold voltage it's going to start shunting and at that point it's going to turn on the opto isolator which is going to signal back to other side and it's going got this control line going all the way back to the switchboard chip the little lamb filtering capacitor here and that's what will turn off so I wonder affair what are the possible problems here we'll to two possible problems to cause that flashing the this side might be sending that as soon as this side spurred it may be sending herself disabled signal back to our side and then not release it until the voltage has gone way too long and then sort of enabling her again there is an interest there's a little chip here oh that appears to be pepper section of circuitry ah right okay this 6-pin connector that screams the back of this is just the Pens positive three pins negative it's the mean five volt supply this looks like it might be an independent supply that's powering going across to power the control circuitry the LCD display perhaps because that's certainly what it looks like okay so my first suspicion here where's the meter is that the the bootstrap circuit may not be working now when these circuits power up initially I'm going to do to this out of fact I shall do delay out and then explain what I'm looking for here so with a typical switch mode power supply you've got their manes coming through some various filtering and a go stripper direct fire and gets converted to DC now this is something confuses people a lot because they say one says convert to DC it's going through a transformer again the answer there is that you can't normally just put DC through transformer but what they do is they convert it back to AC again but at high frequencies that lapse lets me use much much smaller transformer so here's the output the rectifier here's the positive rail here's the negative rail in the case of this this is our UK supply so I'll be about 330 volts and that and there's a smoothing capacitor here that's a big fat capacitor that was glued in place against our heart to her hot transistor block of it and they'll be the switchboard chip which will have its own little power supply what's the best way to draw that here let's say it draw a little capacitor here and that's the power supply for that chip but what happens is this chip can't necessarily power itself it's not you get some trips or Peres directly from this of current limited supply from the means but it's more often to have some trickle charge resistors one or two just going down and trickling that and till that capacitor reaches the voltage that this can turn on that then turns on and it drives the main switchboard chip so that would be driving a transistor I'll just draw a standard NPN transistor here with the primary winding and in normal operation once this chips running it will be switching that one off with very high frequency which is why they can use a small transformer in set with such efficient six otherwise this should have a massive transformer the higher the frequency the smaller transform you can get off with the output that will be going to the other side via diode and a capacitor and that will be the actual low voltage out but there's usually another winding that looks like this and with a diode and it's called a bootstrap circuit what happens is that as soon as there the voltage Ness capacitor reaches a high enough voltage the chip starts running it starts driving the main coil in the transformer that couples current level but also couples current to this small auxiliary winding which is used sometimes just for a power but sometimes also for a feedback signal but in this case as soon as it's powered it charges that capacitor directly via the diode so it doesn't meet those resistors anymore at spouting itself from the circuitry and one of the most common problems that causes that flashing is failure of the winding the diode the capacitor or something in that circuit not working there we've already proven the capacitor is working because it is trying to run so this is one possibility that one of these components is field it could be a dry joint in the transformer let's say investigate that so I've got the meter here set conveniently to continuity continuity should show the waned and continuity let's just test along the primary winding yep getting continuity this is the there's a diode so I should get about point six point six ish volts roughly let's bring us in so you can actually see it point six fourth that's that diode looks alright the solder looks alright round up this say it looks just looks like 10 ohm resistor yeah so it's just there I it's fitting that in the capacitor though aside yes it's fitting this small capacitor that's a bootstrap capacitor the other capacitor next the bootstrapped pastor this one is actually a smoothing a capacitor for the power supply going out to the the logic control on the front circuit board so now what are the windings then nothing I would have expected unless a very high impedance I split it to K nothing I'm not getting anything from the bootstrap winding there pretty sure that is the bootstrap winding and that would suggest if there isn't this solder joints look ok I'm just going to try and probe down into here and see we can make contact nothing I can see the two windings they're coming down that would almost suggest that one of these windings are there is right okay let me show you what I've discovered one of those windings is broken it may be in transit that vibration transformers done that but if we zoom in here and I add a little light into this can you see that little white wire there it's a sleeve doir let me poke that with the probe and it's just off right that square knowing how easy is that going to be to read terminate it's not gonna be easy to read terminate I may have to remove the transformer for that and that is gonna get extremely messy right tell you what I'm gonna start I'm gonna try removing this transformer right now I'm gonna put on there soldier put them each out to the side and if it takes too long if it starts turning into one of those arduous things I shall pause just while I do that because sometimes removing these transformers can be very hard basically speaking it's a double-sided circuit board sometimes it's just you know it's really hard getting the soldier off both sides particularly for such a high mass joint and oh no it's worse it's worse it's worse that's annoying it's trapped under this big heat sink oh that's so annoying right okay let's improvise shall we by trying to strip that and try and solar into that and patch it up back onto the circuit board so it's this connection here which is also going it's no it is it's not it's not as I'm talking crap it it just seems to be doing that feedback I don't think it's doing any sensing it is just power okay so I'm gonna try and very carefully weed all in and get access to that end the sleeve it's just kind of sliding off that's not great because that sleeve is kind of needed to for insulation purposes I'm not sure a good call to this power supply actually is from the text in the front it's not inspiring it says product schematic six USB charger with a digital display by-product schematic it's just like the used words randomly so let's try and slide the sleeve back in oh yes yes that's good and get a bit of wire this is all going to be a bits of rocket surgery and it's also you know what it's also very tight in there and it's very dark you're not going to see a thing in there but I've just stripped that wire back I'm now gonna try and still draw and I tell you what I'm just gonna pause momentarily because this is gonna be very fun Bri and it's all gonna be in there in the dark so you're probably not going to see much so I'll just to pause momentarily and one piece of delicate keyhole surgery later I'll show you what I've done here can you see that what I've done in there it's the wire coming up from the bottom and then tacking on to that wire let's zoom in a little bit let's say zoom rate him and see so that bit of wire that's coming up from there and then tacking onto the lead that's come here at the transformer and to soldier on down there I can actually get soldering iron in there I had to actually hold it in from this side and tin it while heating from the other side so all the heat was applied from this pad here but that is no it back in the socket and I reckon that should work no so there's one way to find out that's to shove it back in and power it back up again incidentally I was going to use let's zoom back out here what was gonna use to try and get that transformer as early as it was trapped in why is these these are still the steel desoldering troops it's a little handle with our stainless steel chip in it and you choose the size that the outer diameter can go through the printed circuit board hole but the inner diameter can go over the pin and you melt the solder and you press this in from one side to other and let it cool and the soldering the stainless steel will not stick to soldiers and you can then wiggle it out and it should theoretically release that can pull mid they work okay so I am let's slide this in and at the risk of it just going bang let's try this out a kind of air just make it move that bit of dirt in there let's remove this circuit board and take a look I could regret this I see what looks like a couple of screws here I may have to use a much thinner screwdriver I'm probably going to regret this completely it's probably never going to go back in again and that isn't that screwdriver and working that is a bit annoying and Dariana do this I don't think I'm going to see an awful lot I think gonna just see USB ports and the LCD display on the other side of the aisle oh I see in there I'll just tap this and see if I can knock that yeah this stuff's kind of yeah come out do that's very professional so this going into the gates here and does that good enough okay well it has its slotted in let's put this flimsy clip on cover what holds us in Latka think that's not very good okay so at note if you have one of yous the back may just pop off right here let's power up and see if it works and it's working okay so that's that solved let's be our lord on it actually you know technically speaking I should do an electrical test in this you know I think I'd rather do that in the circuit board itself one more please I'm going to do an electrical test I'm going to give this a high voltage test from primary to secondary okay testing timings what I've actually done here to restrict the idea that of the structure it gets testimony really interested interesting the isolation transformer I've calmed all the input connections the transformer and the high voltage side to the output connector I've calmed all the other ones in the low voltage side so I'm just purely gonna be testing from one side the transformer to the other selector do the test then let's put this on to a suitable area turn it on and turn the voltage up and I'm aiming for about 2,000 volts here that's 150 that's 300 volts 500 volts 1,000 volts some leakage current but that's through the class wire capacitor is a class by a capacitor I've got to go to 2,000 volts okay that sounds all right I can hear a slight buzzing but you often get that fussing with the test because at 2,000 volts you're reaching the ionization voltage so I'd say that's passed the two thousand volt test nope I have been trying to find out what voltage should be able to test a USB connector a USB power supply for the inputs the hope for and have not earned a decisive answer here I looked at various places they all give different answers the manufacturers were kind of like playing say for the rural voltages and the test sequences all seemed of different random numbers I could have their I could have got a copy of the BS elects a regulations regarding such things but they want to have four hundred pounds of a copy of that so I'm not gonna do that for just two then to rake through it and find one number so am I think yeah well do you guys have any idea what would be the most appropriate voltage range so they said pop these mice ordered link off here let's focus back down onto the circuit board assuming I have focus down onto the circuit board again it's pretty good let's say I get my link off and plug this in again see if I've destroyed it with high voltage is always that slight fear that you may have done something terrible and then after that let's stick a lid on it and see what what it is actually putting out so that's one link off here's the next one I should actually prove some fresh children list because there this is also a fairly large solder joint so it's a just absorbing heat from the soldier and a wee bit that's the peril of large sort of joints I also had sort of an app just run it was sort of that's why I can't famous over here let's flood some new children technically speaking you only need to connect one end of each winding of the transformer because the serve resistance under test of the cheese for windings is actually fairly low so it's the kind of bridge together enemy of the currents we're talking here very delicate when this is not going to spin too long in this one because I you said spending far too long it because this is the one that sort of little wire and the other side and I don't want to err yeah I don't want to risk that wire popping off another side just check those solder joints are all good and also check my wire hasn't popped off the other side with it but sometimes you heat a sort of connection the heat travels through into here affects other components in this case that little wire link type ooh and I'm just making sure it is still sort of yes is so let's put this back together and let's plug a tester into assuming it still works no I versus apt it with 2,000 volts how is this supposed to be stuck on it's got a pattern I wonder if this has been whacked in the shipping and that's why that wires come off and this is kind of cracked it looks as well has been kind of glued or ultrasonically welded in some way but these are kind of recessed that's a bit dodgy that definitely need say stuck together I'm not sure if Paul actually wants this back or if he's a I'll ask him and wants it back that point out this is the situation that's assuming it still works after I've blew in two thousand volts through it let's get a sword road that we while I'm cooking over there sloppy connections here so here's a display five volts and what happens if I plug one of my loads in select a plug this into output five and turn up okay as soon as I could've trying to focus on to this not sure that's going to go as soon as I turn it up to but let's actually point it rate rate up and see if you can actually see this or not zoom in as soon as I turned out the socket five up to about 70 milliamps the position five started flashing let's turn it up higher I'm not sure what their current limit is in these outputs I'd guess two amps typically two point three now it says five volts is it really five volts I should have actually used an hour test from this to see what was happening two point seven amps three amps three point five amps four amps right to what let's let's say that's we're up to four point six amps that's got no real current limiting the five volt and the output of that which is going to suit some projects and let's get there let's get my such a tester and put it in Mexico in lane with outlet to this time and let's zoom down on the snow outlet to isn't even a wise output to not others but the test room five point two two volts is it shoeing yes flashing the outlet to 508 so five bits the voltage is dropping four point nine five volts at about let's got two amps let's go to two point one to point one five four point eight five volts so beyond that the four tails off will be bet but you know what it's showing a little about 2.6 I'd say it's rated for about 2.1 amp power output but i don't know what the rating of the whole thing is I don't know if it doesn't see it doesn't believe on it no there's no data on it a wonderful data on Lane I guess I could go to the shot that came from which was gearbest and I could actually find out if there's data but that does appear to be at fixed anyway that's it working it was I'll show you what that was in this schematic it wasn't a bit I doodled so let's zoom back out and the bit that actually field was this is the bootstrap winding it had failed the connection the wire just popped off there from the solder pin the wired physically snapped from that winding so by bridging that together that's basically restored it to normal operation that can now provide power to itself and that smile at war apply it was actually just doing that pulsing thing what was happening that capacitor was charging up through the resistors it was kicking it was bidding up it was starting the power supply that's nope it was flashing but then because it wasn't providing itself the high current it needed to keep running that capacitor then discharged until it tripped off again and then those resistors just kept trickle charge it until it tripped again I did there until it start again and those were 2 1 mega ohm resistors that were in sears with that so a very typical layout so I say good that it's working I shall contact Paul and see if he wants it back now

Channel: bigclivedotcom

Views: 340,409

Keywords: product schematic, usb, power, supply, charger, faulty, gearbest, repair, repairing, winding, transformer, isolation, flash, test

Id: CkQ9HN7QNNk

Length: 29min 3sec (1743 seconds)

Published: Wed Feb 21 2018

Reddit Comments

[u/Westerdutch]

I just keep waiting for that capacitor 'hand test' to fail one of these days..... the sound he made with the taser module was too funny.