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Old 05-04-2022, 01:37 PM   #1
caprider
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Default ESR 0.6Ω capacitance -15% absolute must change?

I have one (of 3) hot swap Supermicro/Ablecom PWS-0050 SP382-TS server PSU that is mal functioning. Supermicro IPMI reports it as bad and led is orange on.

I took it apart tested transistors, diodes, capacitor but haven't found the problem. I'm a beginner.

In standby I have 5VSB, but not 12VSB, nor 3.3VSB. Here is the PSU Pinot: https://www.rcgroups.com/forums/show...Supply-Convert

There are 3 x 400V, 100uF capacitors on the primary side.

They measure:

- capacitance 85-86 uF
- ESR around 0.55 - 0.65 Ω (I've subtracted 0.15Ω that I measure when I connect my leads together)

I know it's a good practice to change them. But could this explain the whole problem? Or these are workables ranges?

Based on the physical dimension, the 3 caps are a bit expensive if not ordered from China. That's why I'm avoiding to quickly change them.

What do you think?
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Old 05-04-2022, 04:40 PM   #2
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Default Re: ESR 0.6Ω capacitance -15% absolute must change?

That model is end-of-life.

The capacitance is in spec, for +/-20% tolerance. I'm not sure the ESR you measured is abnormal for a 100uF, 400V electrolytic capacitor. It's hard to compare to catalog values, since companies don't seem to publish impedance values for higher voltage parts.

When you apply power, what is the voltage across those capacitors? If it is much below 380V, the PFC stage (assuming it has active PFC) is not working.
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Old 05-05-2022, 05:40 AM   #3
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Default Re: ESR 0.6Ω capacitance -15% absolute must change?

I have 383VDC on the capacitors.

And 242VAC on the bridge rectifier input (mains voltage).
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Old 05-05-2022, 08:07 AM   #4
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Default Re: ESR 0.6Ω capacitance -15% absolute must change?

you will probably find the issue is a small - possibly surface mount electrolytic in flat compact psu's
they are well built, but small caps never last
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Old 05-05-2022, 06:20 PM   #5
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Default Re: ESR 0.6Ω capacitance -15% absolute must change?

So the PFC appears to be working. That plus the 5VSB means your auxiliary regulator is working.

Do you have that 383V at the inverter MOSFET Drain? If not, you may have an open fuse between the PFC and the inverter. If you do have an open fuse, you may have one or more shorted inverter MOSFETs.

Does the controller for the Inverter have Vcc? Do you have the IC part number? Is it on the primary or secondary side?

Does the PWS have 12V and 3.3V Standby outputs? Or simply a 5VSB output with 12V, 5V, and 3.3V main outputs? I suspect it's the latter.
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Old 05-06-2022, 08:00 AM   #6
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Default Re: ESR 0.6Ω capacitance -15% absolute must change?

Quote:
Originally Posted by PeteS in CA View Post
So the PFC appears to be working. That plus the 5VSB means your auxiliary regulator is working.

Do you have that 383V at the inverter MOSFET Drain? If not, you may have an open fuse between the PFC and the inverter. If you do have an open fuse, you may have one or more shorted inverter MOSFETs.

Does the controller for the Inverter have Vcc? Do you have the IC part number? Is it on the primary or secondary side?

Does the PWS have 12V and 3.3V Standby outputs? Or simply a 5VSB output with 12V, 5V, and 3.3V main outputs? I suspect it's the latter.
All of my Ablecom/Supermicro Hot swaps setups (which I'm pretty sure is the same standard as his) are just a 5VSB and (if memeory serves) a single massive 12V main rail. The hot swap "bridge" steps down (buck converters?) the 5V/3.3V rails for motherboard and drive use. ATX12VO before ATX12VO was a thing.
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Old 05-06-2022, 11:28 AM   #7
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Default Re: ESR 0.6Ω capacitance -15% absolute must change?

I should have done this earlier ... here's a pic of one of the 3 modules in a PWS-0050:



It has, as I suggested above, a 5VSB output plus 12V, 5V, and 3.3V main outputs. Also as I posted above, the model is end-of-life, apparently quite a few years ago. You are correct, though, in saying that more modern Supermicro server power supplies are 5VSB or 12VSB and a very high current 12V output.
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Old 05-16-2022, 04:33 AM   #8
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Default Re: ESR 0.6Ω capacitance -15% absolute must change?

Quote:
Originally Posted by PeteS in CA View Post
So the PFC appears to be working. That plus the 5VSB means your auxiliary regulator is working.

Do you have that 383V at the inverter MOSFET Drain? If not, you may have an open fuse between the PFC and the inverter. If you do have an open fuse, you may have one or more shorted inverter MOSFETs.

Does the controller for the Inverter have Vcc? Do you have the IC part number? Is it on the primary or secondary side?

Does the PWS have 12V and 3.3V Standby outputs? Or simply a 5VSB output with 12V, 5V, and 3.3V main outputs? I suspect it's the latter.
Useful questions, thank you. I will dig more for the answers.

Looking for the IC that does PWM I found several op Amps and a PIC.

Is it possible that this PIC is actually performing the PWM: PIC16F819?

Everything is pretty dense with a secondary vertical board with PIC and OP AMPS. I'll have to take down again 3 heat syncs with MOSFETs and double diodes to track pins and see if I missed another IC. Almost all components are covered by the 3 T-section shaped heat syncs.

I'm bringing in today another working PSU (same model) to see if it actually has 12VSB and 3.3VSB (the bad one does not). I also now have a 12V 21W light bulb and test the PSU under load, since it may not output voltages because of zero load.

I assumed this is EOL and I can probably find an alternative replacement. I'm just using this repair project as learning experience.
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Old 05-16-2022, 06:49 AM   #9
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Default Re: ESR 0.6Ω capacitance -15% absolute must change?

After comparing with a good PSU. I see that the bad one is not starting (when connecting PSON and PSKILL to ground). The good one starts the fan, LED turns green and all output voltages are there, without needing a load.

In stand by I have several different voltages on output PINs:

PIN / good PSU / bad PSU

PSON 4.9V 7.9V (and bad one varies a bit)
PSKILL 4.9V 7.9V (bad one varies)
SB5 0.4V 3.3V varies up to 22V
A1 0.5V 1.6V
A0 0.6V 1.6V

I do have 5V on PIN +5VSB on both good and bad power supply.

One bad one is started (pins PSON and PSKILL to ground) LED remains orange, fan does not start, seems to do nothing.

Looks like an issue on the stand by power supply.

Any hints would be appreciated.
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Old 05-16-2022, 12:37 PM   #10
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Default Re: ESR 0.6Ω capacitance -15% absolute must change?

As best I can tell, the PIC16F819 is a general purpose microcontroller, https://ww1.microchip.com/downloads/...Doc/39598F.pdf . Perhaps it is being used as a supervisor.

Your 5VSB is working. The problem is in whatever circuit enables the main inverter, its controller, or in the main inverter itself. Since I lack a schematic, I suggest tracing the enable signal path to find where it stops working or there is some other circuit keeping the inverter disabled.

I suggest making a list of the ICs' part numbers in the P/S and seeing what each IC is. For example, an LM339 is a quad comparator and an LM358 is a dual op-amp.
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