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Old 03-14-2017, 08:06 PM   #1
Agent24
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Default FSP FSP250-50GUB PSU arcing noise, system won't POST.

I'm working on an FSP250-50GUB FlexATX\1U style PSU from a DVR.

I don't know the history, only that it had seen rain, and I don't know for how long. I dried it out before powering it up and it seemed OK. But while the voltages seemed to be in spec, the system did not boot.
With another, standard ATX PSU, the system worked fine.

The capacitors were all OST, except a Rubycon, which looked like it may have been corroded\leaking. I replaced the lot.

However, testing it soon revealed another problem. An intermittent arcing noise from the primary side. I haven't managed to track down the exact component, but it seems to come from the PFC section.
I have checked the PSU in darkness and have been unable to see any spark or such.

Waving my scope probe over the PSU shows bursts of random noise across what are otherwise clean switching waveforms. My current theory is that the arcing component is dumping noise into the power supply so much so that it is propagating to the outputs, and I guess that the output voltages are so noisy that the system won't run.

I was going to try running the PSU without PFC, but the PWM and PFC controller are integrated into the same IC. Of course.


Does anyone have an idea of how to track down the source of the noise and fault? Visually everything seems fine, so far.
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Old 03-14-2017, 11:00 PM   #2
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Default Re: FSP FSP250-50GUB PSU arcing noise, system won't POST.

The photos...
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Old 03-17-2017, 09:38 PM   #3
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Default Re: FSP FSP250-50GUB PSU arcing noise, system won't POST.

Quote:
Originally Posted by Agent24 View Post
I'm working on an FSP250-50GUB FlexATX\1U style PSU from a DVR.

I don't know the history, only that it had seen rain, and I don't know for how long. I dried it out before powering it up and it seemed OK. But while the voltages seemed to be in spec, the system did not boot.
With another, standard ATX PSU, the system worked fine.

The capacitors were all OST, except a Rubycon, which looked like it may have been corroded\leaking. I replaced the lot.

However, testing it soon revealed another problem. An intermittent arcing noise from the primary side. I haven't managed to track down the exact component, but it seems to come from the PFC section.
I have checked the PSU in darkness and have been unable to see any spark or such.

Waving my scope probe over the PSU shows bursts of random noise across what are otherwise clean switching waveforms. My current theory is that the arcing component is dumping noise into the power supply so much so that it is propagating to the outputs, and I guess that the output voltages are so noisy that the system won't run.

I was going to try running the PSU without PFC, but the PWM and PFC controller are integrated into the same IC. Of course.


Does anyone have an idea of how to track down the source of the noise and fault? Visually everything seems fine, so far.
Well if the voltages were fine, you replaced the caps and then you have a new problem. Either you fixed something and the problem was caused by you touching something, or the problem was there, just not as apparent.

First thing I would check would be the places you put your soldering iron near, around all the leads of the caps. Check to make sure nothing got moved or undone by the radiating heat.

The other thing is if water has permeated this PSU, especially rain, this makes me believe it could have left dirt and debris behind causing this. Rain is filled with tons of contaminates. I had rain get into a distributor cap on my car, the marking left behind caused the spark to jump from multiple places at a time, instead of being insulated from jumping to multiple places.

Basically, clean the shit out of this thing, and see what happens.

Another thing could be the chips arcing to one another. If that thermal compound goes conductive, or the insulating/thermally conductive pad or plastic behind it gets damaged from water or even age, it may have this problem as well.
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Old 03-18-2017, 12:37 AM   #4
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Default Re: FSP FSP250-50GUB PSU arcing noise, system won't POST.

I don't know if the arcing problem was originally there, but the PSU wouldn't run the system before I replaced the capacitors anyhow.

The noise is quite faint and I tested the PSU originally in the case and wouldn't have heard it if it had already been present.

I did clean the solder-side of the board already at least, thinking it may have been the issue, but it did not solve the problem.

The joints all look great. It's rather strange.


The three MOSFETs are plastic packages so should be no problem, the PFC Diode is not insulated but the cathode\tab is connected to heatsink anyway through the PCB, so the whole thing is meant to be live. But perhaps current is leaking from the heatsink to somewhere else.

Last edited by Agent24; 03-18-2017 at 12:39 AM..
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Old 03-25-2017, 10:10 AM   #5
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Default Re: FSP FSP250-50GUB PSU arcing noise, system won't POST.

These things like clicking noises etc. are usually PFC problem, especially the coil. I had one such Enermax unit though and even replacing the coil did not help so who knows what was bad…I can imagine some of the film capacitors may have internal arcing though, it would make sense. They are important part of the circuitry, in newer designs they actually move the power to the transformer through them and thay can rarely fail in such manner.
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Last edited by Behemot; 03-25-2017 at 10:11 AM..
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Old 03-25-2017, 03:31 PM   #6
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Default Re: FSP FSP250-50GUB PSU arcing noise, system won't POST.

check out d11 d10 .looks like someone has messed with them .
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Old 03-25-2017, 09:13 PM   #7
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Default Re: FSP FSP250-50GUB PSU arcing noise, system won't POST.

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Originally Posted by Behemot View Post
These things like clicking noises etc. are usually PFC problem, especially the coil. I had one such Enermax unit though and even replacing the coil did not help so who knows what was bad…I can imagine some of the film capacitors may have internal arcing though, it would make sense. They are important part of the circuitry, in newer designs they actually move the power to the transformer through them and thay can rarely fail in such manner.
I remember that, which is why I'm suspicious about it being the PFC coil, also considering it has no signs of physical damage. I'll have a look at the capacitors. Hmm...

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check out d11 d10 .looks like someone has messed with them .
Wrong thread? Or did I miss something?
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Old 03-26-2017, 03:54 AM   #8
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Default Re: FSP FSP250-50GUB PSU arcing noise, system won't POST.

I guess you can only try replacing components one by one, if you have the time…
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Old 03-31-2017, 07:22 AM   #9
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Arrow Re: FSP FSP250-50GUB PSU arcing noise, system won't POST.

Quote:
Originally Posted by Behemot View Post
I guess you can only try replacing components one by one, if you have the time…
This is not a troubleshooting technique. Besides, you will certainly ruin more things than you fix.

You have to decide if the noise is arcing, or a rather normal sound from the switching section when it becomes intermittent.

I agree someone has been replacing parts. Going directly to those areas first is a good idea (check the insulator on the back of the TO-220). Incorrect parts substitution will cause the supply to behave this way.

One approach is to look at the board in the dark - you might see the arcing that way. One more way that is easy is to use a piece of rubber tubing and listen to various spots on the board. I'll bet you can isolate the part very easily that way. But noise by itself does not mean something is arcing.
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Old 03-31-2017, 12:13 PM   #10
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Default Re: FSP FSP250-50GUB PSU arcing noise, system won't POST.

Good luck with that.
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Old 03-31-2017, 05:40 PM   #11
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Default Re: FSP FSP250-50GUB PSU arcing noise, system won't POST.

I can't be sure it's 'arcing' but I can be sure I have never heard such a sound from a normally operating PSU or other equipment before.

I have tried running it in the dark and could see nothing.

Nothing has been replaced except the capacitors. The solder joints were factory with no signs of rework. I do not believe the transistors\diode are anything but original. There is no insulator. The heatsink is tied to the 'B+' rail anyway.

I tried a cardboard tube and it sounded like it was coming from everywhere. But I could try a rubber tube...
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Old 04-01-2017, 11:16 PM   #12
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Default Re: FSP FSP250-50GUB PSU arcing noise, system won't POST.

You have a Samyoung filtering capacitor for the APFC.

Not saying that this is the cause of the problem, but I feel that it certainly is worth mentioning . (Especially after seeing enough APFC circuits hosed by bad caps.)
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Old 04-01-2017, 11:33 PM   #13
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Default Re: FSP FSP250-50GUB PSU arcing noise, system won't POST.

AM radio is a good electrical arc detector.
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Old 04-01-2017, 11:34 PM   #14
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Default Re: FSP FSP250-50GUB PSU arcing noise, system won't POST.

I did check capacity and ESR earlier, and found no problem.

But maybe it is breaking down under full voltage somehow? Or high leakage under full voltage? Hmmm...
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Old 04-07-2017, 01:00 AM   #15
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Default Re: FSP FSP250-50GUB PSU arcing noise, system won't POST.

brown glue corrosion on input choke.
look for more elsewhere.esp pfc.
and these are known for pfc overshoot due to glue.
cap will arc internally till it explodes.
fixed quite a few of these in industrial stuff.
the big cap will literally explode.so watch your face/eyes!
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Old 04-07-2017, 10:21 AM   #16
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Default Re: FSP FSP250-50GUB PSU arcing noise, system won't POST.

I see silicone in there but maybe my glasses are too weak?
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Old 05-07-2017, 09:03 PM   #17
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Default Re: FSP FSP250-50GUB PSU arcing noise, system won't POST.

I can't see any brown glue, but you're right, the input choke does seem to have been slightly damaged. I am not sure by what, though.

PFC voltage is only 390v while the capacitor is rated 450v, so unless there are big spikes? Maybe the capacitor is just failing by itself. Will replace it and see.

Be fun to get a x100 probe and have a look at it too...
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Old 05-08-2017, 12:21 AM   #18
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Default Re: FSP FSP250-50GUB PSU arcing noise, system won't POST.

Can get them quite cheap from fleebay. Some people express concern about the resistor insulation voltage quality, so far both me and my scope survived…
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Old 05-19-2017, 07:20 PM   #19
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Default Re: FSP FSP250-50GUB PSU arcing noise, system won't POST.

Quote:
Originally Posted by kc8adu View Post
brown glue corrosion on input choke.
look for more elsewhere.esp pfc.
and these are known for pfc overshoot due to glue.
cap will arc internally till it explodes.
fixed quite a few of these in industrial stuff.
the big cap will literally explode.so watch your face/eyes!
Well, I don't know if this is related or not, but just saw a PSU at work today with a vented primary cap. It was a Taiwanese brand, so I am not surprised. Will try to take my camera next week and snap a few photos (and maybe even try to fix it, even though we are not allowed to mess with recycle stuff).
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Old 05-20-2017, 06:29 AM   #20
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Default Re: FSP FSP250-50GUB PSU arcing noise, system won't POST.

That's not surprising especially if it's C(r)apXon.
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