- 16 hours ago
120 Watts USB C. type Charger Repairing
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TechTranscript
00:00So today let's analyze this faulty 120 watt gallium nitride charger donated by a viewer.
00:06So big thanks for the donation.
00:08Here is the marking on it.
00:10It's made by NoVoo or whoever that is.
00:13Here are the ratings of it.
00:15It has two USB-C ports, one USB-A port, a European plug in this case.
00:21And now you don't have a deja vu.
00:23I've already analyzed 120 watt gallium nitride charger, but it was a different one.
00:28Now let's test it.
00:30Of course if there is anything to test.
00:32Nothing.
00:33And the USB-C ports.
00:36Nothing.
00:37And nothing.
00:39There is nothing to test.
00:40No voltage coming out.
00:42So the only thing left true is really to open it and analyze what failed in it.
00:47And I have to open it using a saw.
00:49The good chargers typically are not very easy to open.
00:52The very dodgy ones you can just open without anything.
00:58But this one is probably welded, so I make a cut and then I can pry it.
01:05And that's it.
01:07It's going to be all full of resin.
01:11Let's try to pull it out.
01:13That's not going to be easy, I think.
01:17Well, I finally pulled it out.
01:19And here you can see the internals.
01:22There are some shields or heat sinks on it.
01:25And this fold away.
01:28Yes, there is some resin in it.
01:30That's going to be a bit difficult to reveal.
01:32At least no resin on this board.
01:37This is the heat conductive pad.
01:39And of course it's a good idea to discharge the primary electrolytic capacitor in it.
01:43It's this big capacitor here.
01:45Under this cover.
01:47Let's just remove this one.
01:49You don't need it anymore.
01:51And let's remove some of this resin.
01:54Or jelly.
01:55This thing is making it difficult.
01:57It's really not supposed to be opened or repaired.
02:00I'm slowly getting it out.
02:01It's laborious.
02:02It might cause some damage in the process,
02:04but there's really not much left to care about.
02:06This is like dissecting a dead corpse.
02:09Okay, I cleaned this to the point.
02:10We can see everything.
02:11It was quite laborious, so I hope you appreciate my effort.
02:14I also broke this 100kΩ SMD resistor in the process,
02:17so I had to replace it to be able to do the test.
02:20Let's try to figure out how it works.
02:22The mains comes in here.
02:23We have the fuse for fire protection.
02:25The NTC thermistor for inrush current limitation.
02:28Then there is this interference filter.
02:30This double inductor.
02:32This X capacitor.
02:33The yellow box.
02:34Another X capacitor.
02:36This interference separation double inductor.
02:38Another common mode filter.
02:40Then there is the bridge rectifier.
02:42It has four pins.
02:43It's not a bridgeless power factor correction.
02:45It seems to be a standard power factor correction here.
02:48The bridge rectifier goes into this capacitor.
02:50It would go directly into the electrolytic one,
02:52if it was without a power factor correction,
02:54but here it's a power factor correction power supply.
02:57Above 75W it's mandatory for power supplies to have a power factor correction.
03:02The bridge rectifier goes into this film capacitor,
03:04probably polypropylene.
03:06Then via another interference suppression inductor,
03:08it goes into the second film capacitor.
03:11And from this one it goes into the power factor correction,
03:14with this power factor correction inductor,
03:16and some switching transistor,
03:18probably a gallium nitride transistor here.
03:21And from the power factor correction,
03:23it finally goes into this electrolytic capacitor,
03:25which is in this protective sleeve.
03:27It's 420V, 82μF.
03:30And then from this electrolytic capacitor,
03:33it goes into the actual switching power supply,
03:35with this transformer here and some switching transistor,
03:38probably the other one here.
03:40Another gallium nitride transistor,
03:42there is some control chip for the power supply,
03:44the optocoupler,
03:45the voltage feedback.
03:47And on the secondary side of the transformer,
03:49there are two synchronous rectifier MOSFETs with their control chip.
03:52And then it goes into these polymer capacitors,
03:5525V.
03:56And I guess from these ones it goes into the laptop port,
03:59or at least there is a symbol of a laptop on it.
04:02Into this one it seems to go directly.
04:04And into the other ones,
04:05it seems to go via synchronous buck regulators,
04:08with these inductors and some chips,
04:10which probably contain internally some switching transistors,
04:13half bridges for the buck regulation.
04:15Not just a standard buck regulation,
04:17but a synchronous buck regulation for less losses.
04:19Where instead of a MOSFET and a diode,
04:21it has two MOSFETs.
04:22There have to be also some communication chips
04:24to negotiate the voltage with the load.
04:27And thanks to the buck regulators,
04:29these two ports can have a lower voltage than the laptop port.
04:32Now the question is what's faulty here?
04:34We have to shrink the surge down.
04:36It actually seemed that this capacitor had a charge in it,
04:38so it probably is after this stage.
04:41The fuse is good.
04:42All the interference suppression filter is good.
04:44The bridge rectifier is good.
04:46The NTC thermistor is good.
04:48These capacitors are not shorted.
04:50These inductors are not open.
04:52The power factor correction inductor is probably not bad.
04:55But of course we have to try to measure the voltage on this capacitor
04:58to see if the power factor correction is actually running.
05:00If it's not running,
05:01the capacitor will have the rectified mains voltage on it.
05:04230 volts times the square root of 2,
05:07which is about 325 volts.
05:09If it's just this,
05:10it means the power factor correction is not running.
05:12If it's higher than this,
05:13it means it's running and boosting the voltage,
05:16because virtually all active power factor correction circuits work as a boost regulator.
05:21Well, this is dodgy,
05:22but let's plug it in.
05:23I hope I didn't make any damage when cleaning it,
05:26which will make it short.
05:28It doesn't seem to short.
05:29No explosion.
05:30Let's switch my multimeter to voltage.
05:32There is a link in the description to this multimeter and also this USB tester,
05:35which you unfortunately didn't see in use now,
05:38but you could see it in many other videos.
05:40And let's measure the electrolytic capacitor,
05:42hopefully without shorting anything here,
05:44311 volts.
05:46So the power factor correction is not boosting the voltage.
05:49It can mean the power factor correction is faulty,
05:51but it can also mean the power factor correction is not running,
05:54with no or very light load on the power supply.
05:57Which would make sense,
05:58because at no or very light load,
06:00the operation of the power factor correction
06:02would just increase its own power consumption for no reason.
06:05And is there any voltage on the secondary side capacitors,
06:07the polymer capacitors before the buck regulators?
06:10There is actually 21 volts on these capacitors,
06:13which means the isolator power supply,
06:15probably a flyback, is working.
06:17But then why the hell there is no voltage on the ports?
06:20Well, why does it work now?
06:23It didn't work before.
06:25That's odd.
06:26What about the other ports?
06:28The other USB-C?
06:32Well, this one is also working.
06:34What about the USB-A port?
06:36Of course this is dodgy, but
06:44it's also working.
06:47It seems to have been fixed by just opening it.
06:49Or is there some intermitence in it?
06:52Well,
06:54hell yes.
07:03Just by tapping it I actually stopped it from working,
07:05so it has to be some better solder joint, doesn't it?
07:08That's dodgy, isn't it?
07:18Now that it's not working, let's measure the capacitors at the output of the synchronous rectifier.
07:25Two volts.
07:26That's not enough for it to work.
07:28I was measuring these capacitors.
07:30And the power factor correction output in the primary electrolytic capacitor is this.
07:34Which means it's not switching.
07:36The power factor correction transistor is not switching now.
07:39Can I make this video any dodgier?
07:51This capacitor keeps a charge, so it's potentially giving you shocks when you touch it.
07:55Now back to the USB-C ports and these are not working either now.
08:01Nothing.
08:02What about the toothbrush?
08:11Where is the intermitence?
08:13Is it in some tiny SMD component?
08:15I guess maybe this would reveal it.
08:17But maybe this is not the best tool to test intermitence.
08:22It actually takes about a second to come up when the voltage appears.
08:26It's slow, so if the voltage appears momentarily, it doesn't even catch it.
08:31Test equipment can have a delay, so keep it in mind when diagnosing something.
08:35Sometimes even a continued tester can be tricky when it has a turn on delay.
08:40A brief contact doesn't make it beep.
08:46You're for example testing if a certain wire goes to any pin of a connector.
08:52If you do this too fast, you miss it.
08:56And besides the turn on delay, continuity testers can also have a turn off delay.
09:06This produces a continuous beep in this one.
09:09Which is tricky for intermitence testing, because if something's losing contact for short moments, you miss it.
09:14You don't even hear it in this.
09:16Sometimes the most primitive tools are the best.
09:18Let's just solder an LED with a resistor to it.
09:20Okay, that's an LED with a resistor connected to the polymer capacitor at the output of the synchronous rectifier.
09:26And let's see.
09:28The LED is quite dim.
09:30And the brightness is actually fluctuating.
09:33And that's about 2 volts again.
09:38Or is it possible the capacitors are open circuit with a parallel capacitor?
09:43It stopped.
09:44Then it slowly came back as the capacitor charged.
09:52Otherwise it makes no difference.
09:54And connecting a tester or a test load does not make any difference either.
09:58It's still about 2 volts on the capacitors and probably nothing on the ports.
10:04Yes, the actual USB voltage is completely non-existent.
10:07The whole secondary side has just 2 volts on it.
10:10Not enough for any circuitry here to operate.
10:13Now instead of just throwing stones at it and poking sticks into it and similar Neanderthal technology,
10:25let's try to see it on something more advanced like an oscilloscope for the diagnosis.
10:30On the polymer capacitors we can see some voltage fluctuation.
10:33This fluctuation is about 8 Hz only.
10:36It seems the power supply keeps trying to restart and shutting down.
10:40Now let's look at the secondary of the transformer to see the switching waveform.
10:43It's only making extremely short pulses.
10:46And then a long time between.
10:47It seems to measure the frequency wrong here.
10:49It's about 8 Hz.
10:51It's probably because they're super short.
10:53Let me zoom in one of the pulses.
10:55It makes one or a few cycles every time and then shuts down.
10:58Is there something shorted which makes it shut down?
11:01This has to be some protection kicking in, doesn't it?
11:04Overcurrent protection, open loop protection.
11:06We can try to measure on some current sensing resistor.
11:09The current sensing resistors seem to be separate, not built into the chips or transistors.
11:13Of course sometimes integrated chips use the internal MOSFET on-state resistance to sense the current,
11:18but here the current sensing resistors seem to be external, so it's convenient to measure.
11:22This one is for the power factor correction transistor.
11:25It goes from its source to the negative of the main primary capacitor.
11:29This is the flyback switching transistor.
11:32And again its source goes via current sensing resistors into the negative of this capacitor.
11:36Here is 0.1 ohms.
11:38Here it's 0.47 ohms.
11:40And three in parallel.
11:42You can use my online calculator to decode these markings for digit SMD resistor R470 and it tells you it's 0.47 ohms.
11:53Then you can use the other calculators, the CATculator, to calculate the parallel combinations of three resistors.
11:59Calculating the total value of a series combination is simple, it's just all adding, but parallel combinations are trickier.
12:06Let's use this calculator.
12:07And the total resistance of this parallel combination is 156 milli ohms, or in ohms it would be 0.156 ohms.
12:16And that's the resistance we are going to be measuring on.
12:19I connected measuring wires here.
12:21Of course this is the primary side now, so I'm floating the oscilloscope, which is a bit dodgy.
12:26But because it's a battery powered, non grounded oscilloscope, you can do it without shorting it.
12:31You just have to keep in mind the entire oscilloscope's life at minus voltage, including these metal pieces, which are actually accessible.
12:37And I don't really see anything measurable here.
12:39No substantial spikes, which would explain why an overcurrent protection would trip.
12:46The primary voltage would be about the same as the secondary voltage, I don't see a point of measuring it.
12:51It's just going to be larger and a very very low duty cycle, which is what gets the very low voltage 2 volts to the secondary side.
12:58We can try to test the optocouplers, the LEDs in them.
13:01And of course after I unplug it, I always discharged the capacitor using the LAMP.
13:04This is the infrared LED in one optocoupler.
13:07And the other one also seems to have a good LED in it.
13:10Let's try to measure the voltages when it's on.
13:13It's a bit dodgy of course, but this optocoupler, no voltage on its LED.
13:17This one a way too low voltage for it to glow.
13:20So there is basically no feedback going through.
13:222.8 volts on this transistor of the optocoupler, or phototransistor actually.
13:27The phototransistor of this one has no voltage on it.
13:30It's for some reason actually going slowly up.
13:32I'm not sure why two optocouplers in one power supply, but it could be one is the feedback for the flyback power supply.
13:38And the other one enables the power factor correction above a certain load.
13:42But anyway, given it momentarily started to work normally, there has to be something intermittent.
13:47Failures in semiconductors, especially power semiconductors, are generally not intermittent.
13:52A failure of a power semiconductor is typically avalanche and completely catastrophic.
13:56I still think it could be a bad solder joint.
13:59Or maybe some intermittent short turns in the transformer.
14:02Or maybe the inductor.
14:03Of course having a ring tester we can ring test the transformer.
14:06You typically ring test the primary.
14:08Where is the primary?
14:09There are four pins.
14:10Two are the auxiliary, two are the primary.
14:13One terminal of the primary should go to the drain of the switching transistor.
14:17It's this pin.
14:19And one pin of the primary should go to the positive of the main capacitor.
14:22Of course I discharged it.
14:24That's this pin.
14:25So the two pins on the top are the auxiliary.
14:28And at the bottom the primary.
14:30So let's ring test the primary using my DIY ring tester.
14:33Thirty rings.
14:34That's quite a lot.
14:35No winding in the transformer should have short turns if it reads this.
14:39There is the inductor in the power factor correction.
14:42We can also ring test this.
14:44Forty two rings.
14:45Quite a lot.
14:46So the power factor correction inductor is also not shorted internally.
14:49Unless the problem now magically went away.
14:52Let's try.
14:53The LED very slowly came up.
14:58Very dim.
14:59There has to be about two volts again.
15:01So I don't think it's short turns or intermittent short turns in anything.
15:05Let's also check the current sensing resistors.
15:07Of course such low resistances are difficult to measure.
15:10The meter doesn't have the resolution for it.
15:12The resistance of the tips and cables skews it.
15:14But if it reads less than one ohm, they shouldn't be open circuit at least.
15:18The current sensing group for the flyback also isn't open.
15:21Let's try this one.
15:22This is a battery internal resistance tester.
15:25It's meant for the internal impedance of batteries.
15:27But it surprisingly can also measure DSR of capacitors.
15:30Electrolytic ones.
15:31And even very low resistance resistors.
15:33Even it has Kelvin connections.
15:35Kelvin probes.
15:36That's the 100mΩ resistor.
15:38It measures it quite accurately.
15:40And the three parallel resistors in the flyback current sensing.
15:43This one was never meant for it, but it measures very low resistances super well.
15:48Let's measure the primary electrolytic capacitor with this one.
15:51700mΩ.
15:52That's not bad.
15:53And this one has about 400mΩ.
15:56It actually reads a bit less always because this is using 100kHz.
15:59This one is using just 1kHz for the test.
16:02Let's also try the polymer capacitors on the secondary side.
16:06Just 6mΩ.
16:07And they have a super low ESR.
16:09And this time paradoxically this one reads more.
16:12But that's because this one is not using Kelvin probes.
16:15So extremely low impedances are skewed by the impedance of the cables.
16:19But nevertheless I don't think the capacitors are bad given these low readings.
16:23And of course bad capacitors, especially electrolytic ones, could definitely cause intermittent problems.
16:28It's way more likely than semiconductors causing intermittent.
16:31I still think the most likely cause is a bad solder joint.
16:34But it's difficult to locate.
16:36There are so many of them and super tiny.
16:38He removed some of the test wires to prevent accidentally shorting something.
16:42Switching power supplies are one of the least forgiving circuits.
16:45Any momentary short circuit can cause an explosive destruction of many components.
16:49Let's try poking it once more.
16:53But it could be something on the other side, which I wasn't poking much yet.
17:08How did it momentarily come back to life?
17:17It happened after I removed the resin from it, so I probably moved something.
17:23And then it stopped working when I was knocking it with the screwdriver.
17:27It has to be something sensitive to movement or vibrations or shocks.
17:33I left this capacitor to poke under it.
17:43When this thing is going to explode.
17:45He keeps poking absolutely everything and he can't figure out where the intermittence comes from.
17:50What about heat sensitivity or thermal expansion?
17:53What if I heat it with my melted hair dryer?
17:59I also tried heating the other side of it nothing.
18:01I've left it outside for a couple hours at minus 2 degrees Celsius.
18:05Does it change anything?
18:10Still the same.
18:11Well, let's actually see the primary waveform anyway.
18:14It technically should be the same waveform as the secondary, just a higher voltage, but that's in theory.
18:19In reality no transformer has a perfect coupling, so the waveform can be different.
18:23Real transformers have a leakage inductance, which basically acts as if some of the windings had a series inductor.
18:29I'm connecting the ground the clip of the non-grounded oscilloscope to the end of the primary,
18:33which goes to the rectified main as positive, because there is no high frequency voltage.
18:38And the tip of the probe goes to the other end of the primary, which goes to the drain of the transistor,
18:43which has a lot of high frequency voltage on it.
18:45And of course I'm using a times 100 probe, 2kV.
18:48We have again the very short pulses.
18:51Let's zoom them in even more than before.
18:54We have to choose a single trigger mode.
18:58It seems to make every time 4 pulses.
19:01Let's zoom one of them even more, the first one.
19:05Peak to peak about 312 volts, which makes sense.
19:09This is the primary capacitor voltage.
19:12And its own half microsecond pulse, then some ringing.
19:16It makes 4 such pulses and gives up for about 120 milliseconds.
19:21It's trying to start up, but gives up after just 4 switching cycles, which seems way too few.
19:26It does not seem like the typical condition, when the power supply is trying to start and something is shorted on the secondary side,
19:32because in a short circuit condition typically the startup attempt is much longer.
19:36Basically 4 switching cycles would not even charge the secondary capacitor, would they?
19:41A high resistance resistor, the startup resistor, typically several megaohms,
19:45charges a low voltage capacitor on the primary side, and this one then powers the chip.
19:49The control chip on the primary side, which controls the MOSFET or other switching transistor.
19:53And once it's already switching, the auxiliary winding powers the chip,
19:57because the startup resistor doesn't supply enough current for the chip to continuously operate.
20:01So if it fails to start up, the auxiliary does not supply enough voltage for the chip,
20:06so it only runs from the capacitor until it runs out of charge.
20:09And then the capacitor recharges, then it might retry to start up.
20:13This is a typical situation when the secondary side is shorted,
20:16the switching power supply is then trying to restart in low frequency pulses.
20:20Not actually individual pulses, but so called bursts.
20:23Every pulse is actually a series of high frequency pulses.
20:26Something like this, but every group of pulses actually is several hundred or even several thousand.
20:31Is there something shorted on the secondary side?
20:33Because if the secondary is shorted, it basically pulls the voltage down on all windings,
20:38and that's why the auxiliary can't supply enough voltage to power the chip.
20:41In such condition only the startup resistor powers it and,
20:44because it supplies less current than the chip draws, it doesn't keep trying continuously.
20:49It's only trying until it runs out of the charge in the capacitor and then it's waiting for the capacitor to recharge
20:54before the next starting attempt.
20:56But the question is, is this actually the case with this power supply?
20:59Even the startup attempts are much shorter than this condition I'm describing.
21:03It might be something shorted on the primary side, maybe.
21:06But they came up with an idea.
21:07Let's try to use a bench power supply and backfeed about 20 volts into the secondary side of this power supply
21:13to see if it's possible without it drawing an excessive current.
21:16And maybe if the back regulator actually regulates the voltage to let's say 5 volts for the ports.
21:21This could basically diagnose the secondary side separately.
21:24Because at this point we don't even know if the problem is on the secondary side or the primary side.
21:28Let's use my old power supply and voltmeter.
21:32The current limit is set to just 0.2 amps for the first test.
21:36And let's try to increase the voltage.
21:38It doesn't draw much.
21:40Let's go up to 20 volts.
21:42It still draws almost nothing.
21:44And hell yes.
21:45It actually produces 5 volts on one of the USB ports.
21:49Let us load this now at 0.
21:51I will increase the current.
21:52I will also increase the current limit on the power supply to half an amp.
21:55Now the output voltage of the back regulator is one quarter of the input voltage.
21:59Which means it should draw from the power supply.
22:01About one quarter of the current I'm drawing from the 5 volt output.
22:05If I try to draw 1.6 amps, let's say, it only draws 0.4 amps from the power supply.
22:12Plus maybe a little bit extra for the losses.
22:14And that actually works really well.
22:16Let's increase the current limit.
22:18I'm drawing 2 amps.
22:19And it only draws from the power supply half an amp.
22:2220 volts times 0.5 is 10 watts.
22:25And 5 volts times 2 amps is also 10 watts.
22:28Of course in reality, because of some losses, it has to draw slightly more.
22:32But back regulators are very efficient.
22:34Well over 90%.
22:35So this USB-C port actually works.
22:38The other one.
22:39It also works.
22:40It again back regulates the 20 volts to 5 volts.
22:43The USB-A port.
22:46Of course now it's the power supply.
22:48It's not connected to mains.
22:50So it's safe to touch at 20 volts.
22:54And even the USB-A output is working.
22:57Now drawing about one amp and switching to other voltages.
23:009 volts.
23:0212 volts.
23:04It works.
23:05This one probably can't do 20 volts.
23:07One of the USB-C ports.
23:09It also works.
23:10This one goes up to 20 volts.
23:12But of course back regulators can only regulate down.
23:16So when I set it to 20 volts it only produces 19 volts.
23:19It seems the back regulator can run up to about 95% duty cycle.
23:23But if I increase the voltage of my bench power supply a little bit to let's say 22 volts.
23:28It can now regulate 20 volts.
23:30It seems to require at least 21 volts at the input for a 20 volt output.
23:35And the other USB-C output also works.
23:40When the charger was momentarily working, the synchronous rectifier output was about 22 volts, which makes sense.
23:47So if backfeeding voltage into the output of the flyback switching power supply makes it work, the problem has to be on the primary side, doesn't it?
23:55I guess the problem has to be somewhere near the control chip of the flyback.
23:59And some components near the auxiliary winding.
24:01It's a diode rectifying the auxiliary.
24:04And then it goes via this 2 ohm resistor into a small electrolytic capacitor 10 micro 50 volts.
24:10Of course I should have measured this one when measuring the other capacitors.
24:13Because if this one was bad it would definitely cause some problems here.
24:172.4 ohms, which is definitely unacceptable ESR for such small capacitors, just 10 micro.
24:23If it was a higher capacitance it would be bad at 2 ohms, but for just 10 micro that's normal.
24:28Using a diode test I can also check the capacitor for a short, it's not shorted.
24:33And the other meter about 3.7 ohms, but it's normal for it to read about 50-60% higher than the other one.
24:39So it's not this electrolytic capacitor, but about the other components here.
24:43There is a diode and the resistor. It really seems like some of them has to be open,
24:47because it's acting like the chip is only powered by the startup resistor,
24:51which in case of SMD components is typically 2 or 3 resistors in series,
24:55because of the high voltage, and the chip doesn't get its power from the auxiliary.
24:59So the diode going from the auxiliary is not open circuit.
25:03And the resistor, it says 2 ohms, reads 1.8 ohms, but it's not a problem.
25:09But what else can go wrong here?
25:11One more diode here, again a good diode.
25:15This is probably a Zener, a good diode.
25:18There's some big ceramic capacitor, it's not shorted.
25:21This ceramic capacitor not shorted, I can see some diode parallel to it.
25:26The chip can't be bad, because typically when they fail, they fail completely.
25:30The one still produces pulses for the gate of the transistor.
25:33I'm not even going to measure all the components on camera, I'm just checking the diodes,
25:37the ceramic capacitors for short, out of desperation maybe even the resistors.
25:42But what can go wrong in the circuit powering the chip? It's very simple.
25:45It's just the auxiliary going through a diode and a resistor into its capacitor on its supply rail.
25:50Am I getting something wrong here?
25:52These two pins have to be the primary.
25:54This is connected to the positive of the main capacitor.
25:57And this one also beeps, because it's connected with it via the primary winding, which is for DC a very low resistance.
26:03And if the transformer on the primary side has 4 pins, the other two have to be the auxiliary.
26:08One end of it is connected with the negative of the main capacitor, and the other one...
26:13What the hell?
26:16This one is connected to the negative of the big capacitor.
26:20And this one should also beep, because it's just several turns of a thick wire.
26:24What can go wrong with probably no more than 10 turns of a thick wire?
26:28It's measured directly between the pins of the auxiliary, or at least what I suppose is the auxiliary.
26:33How this can be open?
26:35Am I getting something wrong?
26:37It just can't be any other way.
26:39This is the cold end of the primary going to the positive of the main capacitor.
26:42This is the hot end going to the drain of the transistor switching.
26:46This one is the hot end of the auxiliary, which goes via the diode and the resistor into the chip capacitor and its supply rails.
26:53So then this one would have to be the cold end of the auxiliary, going to the negative of the main capacitor.
26:59The transformer doesn't have any other pin on the primary side.
27:02Connecting these clips on the auxiliary, it's still open.
27:05Is there some bad contactor?
27:06Was it dropped and it broke the pins?
27:08There is not much to fail on winding with a low number of turns.
27:12If I push the transformer, or if I push here...
27:16Well, when I push the transformer, it sometimes makes contact.
27:29This has to be either a bad soldering or it was dropped.
27:32Let's just power it and see what happens.
27:35And when I push here, it actually comes back to life.
27:40This is dodgy, but no, it doesn't work.
27:44Push.
27:45And it works.
27:49I slightly lift the transformer.
27:51Doesn't work.
27:53I push.
27:54It works.
27:58So that's basically it.
28:00Let's try to test load.
28:02I can load it up to 3 amps and it works.
28:08But when I lift the transformer, it stops.
28:11So I finally found it, but it took some time.
28:13One more test.
28:14Let's try to switch the voltages 9, 15 and 20.
28:18It produces 60 watts, 70 watts, 84 watts.
28:25And it still works.
28:26Nice.
28:27When it's not making contact here about 2 volts.
28:30When I push, 21 volts.
28:33It seems to be stable from no load.
28:35All the way to the maximum of my test load.
28:38Basically going from no load.
28:40284 watts.
28:42The problem is identified, but now of course I should
28:45desolider the transformer and look under it and see what's broken.
28:48Is it the pin itself or is the winding separated from the pin?
28:51Or maybe some measurements before that.
28:54318 volts.
28:56And when I increase the load, what happens?
28:58Let's go actually slowly up with the power.
29:01At about 34 watts, the power factor correction starts operating.
29:06And boosting the voltage to 370 volts.
29:09Let's go slowly down.
29:10I assume there might be some hysteresis.
29:13Of course.
29:14At about 29 watts, the power factor correction stopped running.
29:18To improve the efficiency at late loads, the power factor correction is not running.
29:22And this video is getting bloody long.
29:24I should do the autopsy of the transformer, but I'm curious about the waveforms and switching frequencies here.
29:29Let's connect an oscilloscope to the source, gate and drain of this transistor in this active PFC.
29:35It might be interesting to see the gate waveform, which in a gallium nitride transistor is probably different than in a MOSFET.
29:41This thing would be fixable, but the main point here is to learn something.
29:45I might short something and blow it up, connecting all the test wires, but this thing is probably heading its autopsy anyway.
29:52Ok, the probes are connected to the transistor.
29:54Of course the ground leads go to its source.
29:57A times 10 probe to its gate and times 100 probe to its drain.
30:01And again a dodgy oscilloscope floating time.
30:04And that's it.
30:05Nothing happening until I increase the load above about 34 watts.
30:09And then you can see it switching.
30:11This channel is the gate, 2 volts per division.
30:14And this channel is the drain, 200 volts per division.
30:18Of course everybody is screaming, put it closer to the camera.
30:21The power factor correction is switching at 130 kilohertz.
30:24And of course the duty cycle is dynamically changing, as it's riding the 100 hertz ripple,
30:29the rectified but unsmooth mains.
30:31And when I stop it, it actually shows a bit different duty cycle every time.
30:38You can see the gate of the transistor goes up to about 6 volts when it's on.
30:42Less than in a typical high voltage MOSFET.
30:44But when it's off it's actually slightly below zero.
30:47Now showing just the gate of the transistor.
30:50One volt per division.
30:53Now the load is about 30 watts.
30:55Let's try to increase it.
30:57All the way to 84 watts.
31:00And let's go back down.
31:02It doesn't seem to change much, does it?
31:04Why could be load threshold about 29 or 30 watts and it turned off.
31:09Let's go back up.
31:11And it runs again.
31:12You should also show the current sensing resistor, shouldn't I?
31:15Now the upper one is the transistor drain and the lower one is the current sensing resistor.
31:19There is quite a lot of ringing in it, but here you can see the current going gradually up as the transistor is on.
31:25And the magnetic field is building up in the power factor correction inductor.
31:28When the transistor turns off here, the voltage goes up to the 370 volts and charges the capacitor.
31:34That's how it boosts the voltage.
31:37It accumulates some energy in the inductor here and then it adds the inductor voltage to the mainest voltage.
31:43Now just the current sensing resistor.
31:4550mV per division.
31:46This is sensed on a 100mA resistor.
31:49It shoots 500mA per division.
31:51The PFC transistor is on from here to here and you can see how the current goes linearly up with the magnetic flux of the core in the power factor correction inductor.
32:00Now I've connected the oscilloscope to the source drain and gate of the flyback transistor.
32:05And let's plug it in with the drain source voltage and the gate source voltage.
32:12With the 40W load it's running at about 63kHz.
32:16Now the frequency is changing with the load.
32:18Reducing the load.
32:2010W.
32:2120W.
32:2240W.
32:2460W.
32:2584W.
32:27That was 104kHz about.
32:30But it seems to be always discontinuous conduction mode.
32:33Let's hit about 50W and let's zoom it in a bit.
32:36Here the gate has about 6V on it.
32:38The transistor is on.
32:40Here it turns off and the synchronous rectifier is conducting and charging the secondary capacitors.
32:45And here it's ringing.
32:47And there is no current for some time before the transistor turns back on.
32:51Typical for a discontinuous conduction mode and when I change the load it seems to be almost a constant on time.
32:58Except very light loads.
33:00And the frequency goes up with the load.
33:03And again you can see a slight negative turn of voltage for the gate here.
33:10Which seems to peak at about minus 600mV.
33:14The drain and the current sensing resistor.
33:16The drain to source voltage and the current sensing resistor voltage.
33:19A 40W load.
33:21The frequency goes down again with less load and up with more load.
33:25Here the transistor is on.
33:27Let's zoom it and you can see the current again going gradually up as the transistor is on and the magnetic field builds up in the flyback transformer.
33:35And the energy is being accumulated in its ferrite core or in its air gap.
33:39And when the transistor turns off then the energy goes through the synchronous rectifier MOSFET to the secondary capacitors from here to here.
33:46And the peak current doesn't actually seem to change much with the load.
33:49Only the frequency of the pulses going down with the load.
33:53It's lower only at very light loads and then it doesn't go up much from about 30W all the way to 84W.
33:59No 84W and 200mV per division on the three parallel resistors.
34:04You can kind of guess the peak current from this yourself.
34:07I will try to measure the synchronous rectifier transistor's gate.
34:11That's the primary transistor drain to source and the synchronous rectifier transistor gate to source.
34:17You can see the synchronous rectifier transistor has a positive voltage on its gate after the primary transistor turned off.
34:23It's odd how the voltage is declining on the gate.
34:26You can take a closer look here.
34:285V per division so it starts at about 7-8V and it declines to about 4V barely.
34:34But of course most of the current goes through the transistor at the beginning.
34:37Then the current reclines as the energy runs out in the transformer core.
34:41Let's increase the load up to 84W and reduce it.
34:47That's it at 40W.
34:49Let's zoom it way in.
34:51There is a small delay between the primary transistor turning off and the secondary side synchronous rectifier transistor turning on.
34:58And one of the buck regulator inductors when the USB-C output is 5V, 9V, 15V and 20V.
35:08About 30W load going down to 0 and up to 84.
35:13Not much change here.
35:16It's using a constant 126kHz frequency.
35:20Now 5V full 3 AMUPS and going down.
35:24Virtually no change until I get down to 0.4 AMUPS.
35:28Then it gets into a discontinuous conduction mode.
35:31Otherwise it seems to be a continuous conduction mode.
35:34And a small correction.
35:35It seems none of the USB ports is connected directly to the flyback output.
35:39I'll go via the buck regulators with these two inductors.
35:42I guess this USB-C port shares the buck regulator with the USB-A port.
35:46Because when something is plugged into this USB-C port, the voltage disappears from the USB-A port.
35:52So you can probably just use one of these two.
35:55Now the tester is in the USB-A port instead of the USB-C port.
35:59And it's using the same inductor.
36:015V, 9V, 12V.
36:05The USB-C port seems to have a priority over the USB-A port.
36:13The other USB-C port.
36:16This one is charging my phone and this thing is still running.
36:20Now let's try to disolder the transformer.
36:23So that's the transformer disolder.
36:25And one of the auxiliary pins has a tendency to come out.
36:29And the wire separated from it.
36:31You can still see a little bit of the wire wrapped around the pin.
36:34But it broke off.
36:35It was probably dropped.
36:37An even closer look.
36:38You can see the end of the auxiliary winding here.
36:41Which broke off this pin.
36:44If anybody wanted to see what was under the transformer.
36:51And this transformer could be fixable.
36:52Well, I've already fixed it if pushing it counts as a repair.
36:56But I guess everybody rather wants to see the internals of the transformer.
36:59Should start opening it.
37:01Some marking on it if anybody is interested.
37:03A lot of tape around it.
37:05And the secondary wires.
37:07And some interference shield connected to the cold end of the auxiliary.
37:13Which is connected to the negative of the primary side.
37:16This is a return path for the capacitively coupled high frequency current back to the primary side.
37:21But this part of the copper is also a short turn for any magnetic flux.
37:25Which would try to take a different path than through the frayed core.
37:28It removes the copper.
37:29Now removing this sticky tape around the core.
37:32Let's try the melted hair dryer.
37:34Let's try the melted hair dryer.
37:35Let's try the melted hair dryer.
37:39That's the frayed core of the flyback transformer with an air gap in the middle, of course.
37:54the transformer wire rings with this sticky tape on top.
38:01This seems to be one half of the primary. There is a pin which doesn't go into the board. It's
38:11the center point between the lower and upper half of the split primary for better coupling.
38:15The primary is not one solid wire, it seems to be a high frequency cable made of multiple twisted
38:21thinner wires to reduce the skin effect at high frequencies. A higher frequency allows
38:26the transformer to be smaller at a given power, but it requires faster transistors and this
38:31skin effect mitigating technique, of course. And you can see the ends of the windings have
38:36sleeves to prevent them from coming into contact with something else, especially near the edges
38:41of the sticky tape under the winding. Let's cut the winding and unwind it.
38:471, 2, 3, 4, 5, 9, 10 turns. Then the insulation under it. One layer, two layers. And then something
38:59that looks like winding made of two parallel wires, but one end of it is loose. So this
39:03is probably just an interference shield. Let's unwind it. 1, 18, 19, 20 turns. It goes to the
39:11cold end of the auxiliary, which basically is used because it has no high frequency voltage
39:16on it. Then another sticky tape. One layer, two layers, three layers. And this is the secondary,
39:25it seems. A very thick wire with a very thick safety insulation. Probably a triple insulated
39:30wire. 1, 2, 3, 4, 5 turns of it. And for even more safety sleeves at the ends of it. One is black, one is transparent. This is to mark the direction of the wiring.
39:44Because in a flyback power supply, the ends of the wiring are not interchangeable. Then again a tape. One layer, two layers. And here is the auxiliary. The end of it again have sleeves and it's one, two, three, four, five turns. Again a tape. One layer, two layers. And the bottom half of the primary. In some cases the halves are equal, but sometimes the bottom half has more turns. It seems to be the case in the
39:51here. One, two, eight, nine, ten. One, two, eight, nine, ten.
39:58And it's the same high frequency cable as the top part of it.
40:0518 strands of a 0.1 mm diameter. And the secondary. It can also measure its length and resistance. It has de-insulation on it and a lot of strand.
40:12It's again 0.1 mm. It's again 0.1 mm but there is 90 of them.
40:19Using the calculator wire resistance calculation, if copper wire has 9.3 mm resistance and it's 329 mm long, it's going to be the same.
40:26It's the same high frequency cable as the top part of it.
40:2818 strands of a 0.1 mm diameter. And the secondary. It can also measure its length and resistance. It has de-insulation on it and a lot of strands.
40:34It's again 0.1 mm but there is 90 of them. Using the calculator wire resistance calculation, if copper wire has 9.3 mm resistance and it's 329 mm long, its cross section has to be 0.62 mm.
40:52And of course the diameter calculation is irrelevant here because it's not a single circular conductor.
40:57We can also calculate the cross section based on the wire diameter 0.1 mm. That's the cross section of one strand. And of course I have to multiply it by 90 for the secondary. To get the total cross section of 90 strands.
41:12Which in total is 0.71 mm. But it's probably overestimated, because it's difficult to measure such thin wires and I'm measuring it with the locker on it.
41:21This slightly lower total cross section, calculated from the length and resistance of the wire ring, is probably more realistic.
41:28And here is the entire reverse engineered transformer. And given the primary has the same strands, but one fifth of them, its total cross section probably is one fifth of this.
41:38And here is the pinout of the transformer. And the marking of the flyback transistor. And the power factor correction transistor, which probably is the same thing.
41:47And its control chip. And the flyback control chip. And on the secondary side the synchronous rectifier MOSFETs and their control chip.
41:56And some Y1 safety SMD capacitors between the primary and secondary side. And probably the synchronous buck regulator chip.
42:03Of course I could look at the datasheets, but just look at the length of the video.
42:07Just the gallium nitride transistors. Which are basically the main selling point of the charger, aren't they? Both are the same type.
42:14700 volts, 240 milliamps on state resistance. The gate source continuous voltage is quite low, in comparison to standard MOSFETs.
42:22But a surprisingly high pulsed negative gate source voltage here. And the gate threshold voltage is also quite low, in comparison to high voltage MOSFETs.
42:31The threshold is like low voltage logic MOSFETs. Like 30 volt ones. But note that, just like in normal MOSFETs, the on-state drain source resistance still goes up quite steeply with the temperature.
42:43And the capacitance's charges and switching characteristics. Quite low gate capacitance, output capacitance, extremely low reverse transfer capacitance, or miller capacitance, drain to gate.
42:54And these switching times are just 2, 4, 5, 6 nanoseconds. It's an extremely fast transistor, isn't it? And a very low gate charge.
43:03So that's it, quite an interesting and a nice charger, which failed anyway. But it's difficult to tell whether the auxiliary pin connection was already somehow weak from the manufacturer, or if the charger was dropped from a height.
43:14And it's sad I have to mention it, but this video was not produced by AI. It was produced by a real human and a ton of effort.
43:23So if anybody made it that far, please consider supporting my non-AI channel on Patreon, using the thanks button, or at least subscribing, and big thanks to all of you who already support me.
43:34Without your support, channels made by real humans will go extinct.
43:38For people at least they'd better be extinct.
43:52And I'd appreciate it.
43:55I'm sure if somebody feelsingenck for this two seconds and this nuisance thing and it is still not okay, you're by two pockets.
43:59In this time I can't see it, I won't진ct.
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