Troubleshoot desktop computer with Gigabyte P750GM PSU

[Adenitz]

Hello guys,

I have a problem with a desktop computer that cannot start (cannot turn on when pressing the power switch).

I know for sure that power supply is Gigabyte P750 GM, but I cannot tell the manufacturer of the motherboard (LGA 1331). All I can read is the following number on the sticker: 706023 - 01460 - MB1180 - b05 1407.
Motherboard is most likely Gigabyte X570 AM4

The problem is that computer cannot start when power switch is pressed.
So I first tested the PSU. I have plugged out ATX 24 pin power connector from the board and use paper clip to short pins 16 and 17. When I do this, PSU starts and I can measure all voltages (3.31 V, 5.01V, 11.99V). They seem stable. So at first I suspected motherboard, but then I noticed something that I find odd.
When power cable is unplugged, each time I connect pins 16 and 17, there is a clear click sound inside the PSU.
The owner of the PC says it didn't die suddenly. Two or three times before this happened, computer also didn't start, but it needed a few times pressing power switch to start.

I have tested the power switch (multimeter in continuity mode) and it works OK. Each time I pressed power switch, the resistance between to leads drop to 0.1 ohm.

Can you advise me what to try next? I would try to test it with another PSU, but I'm interested to learn if this clicking sound in the PSU (with no power) OK when shorting pins 16 and 17?

Thank you.

[Adenitz]

Re: Troubleshoot desktop computer with P750GM PSU

Here is the update.
When testing with other PSU, computer started without problems.
So PSU is to blame even though it is old a little less than 3 years.
When cover is removed, there are two bulged capacitors visible.
One cap is 1000 uF, 10V, other is 2200 uF, 10V.

I will replace them and hope for the best.
Just want to say that testing PSU by shorting pins 16 and 17 together is not 100% reliable, because I could measure all voltages and they were stable at nominal values. This PSU could also power chassis fans but this was not enough to start the computer with a Nvidia RTX 175 W graphics card.

Attached is a picture, does anybody can say what these two caps are used for. Since they are 10V rated, they are probably on 5V or 3.3V output line.

[Per Hansson]

Re: Troubleshoot desktop computer with P750GM PSU

Attached is a picture, does anybody can say what these two caps are used for. Since they are 10V rated, they are probably on 5V or 3.3V output line.

Most likely they are for the separate 5VSB power supply.
Notice their proximity to that small transformer and what I would imagine is a 8-pin 5VSB control IC right next to it.

[Adenitz]

Re: Troubleshoot desktop computer with P750GM PSU

Ok,
so because this is for 5V standby, that is the reason why PC cannot even start and doesn't show any signs of life when pressing power switch.
I have found this article, but this PSU serial doesn't belong to the specified range, so it doesn't qualify for the RMA.
Nevertheless, I think it's a shame that PSU works only 4 months after warranty period is elapsed.

BTW, this thread should probably be moved to PSU subforum.

[stj]

Re: Troubleshoot desktop computer with Gigabyte P750GM PSU

when you replace them, replace the other one with the same vent style higher in the picture.

[Adenitz]

Re: Troubleshoot desktop computer with Gigabyte P750GM PSU

I will, thank you.

[Adenitz]

Re: Troubleshoot desktop computer with Gigabyte P750GM PSU

I have exchanged faulty caps + one more as suggested. PSU now works OK. Output wires are not coloured, but I noticed there are now two stable voltages when PSU is off. One is 5.04V and this is most probably 5VSB. Other is 4.7V. This is most probably PSON that will be pulled low when power switched is pressed.
Thank you for your help. Greatly appreciated.