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Electronics => Repair => Topic started by: PlainName on September 29, 2024, 07:07:01 pm

Title: ATX PSU
Post by: PlainName on September 29, 2024, 07:07:01 pm
Got a CoolerMaster 600W ATX2 wired PSU. Was fine yesterday, PC won't power up today.

I think the 5V standby is OK (the motherboard start and reset buttons light up), although I am seeing 2.5V on PON. Pulling it down does nothing. However, putting an ATX PSU tester on it (which doesn't apply much, if any, load) sees the PSU come alive and all the voltages read correctly. Seems to be a decent load (like a motherboard) that stops it from starting.

Is there a typical fault that would cause these symptoms?

(To head off the obvious, I verified the motherboard will power up with a weedy ATX1 PSU.)
Title: Re: ATX PSU
Post by: m k on October 04, 2024, 05:30:45 pm
Bulky capacitor maybe.

Usually that is not enough though, for the power supply, but maybe motherboard has sensors.
Title: Re: ATX PSU
Post by: The_Spectrum.A_idiot on October 04, 2024, 05:55:47 pm
Similar issue was caused on Synology boxes in the past , the solution was adding a resistor on the PSU start line.

But inherently it was a CPU / MOBO issue.
https://community.synology.com/enu/forum/1/post/136284 (https://community.synology.com/enu/forum/1/post/136284)
And from the man himself
https://www.youtube.com/watch?v=Y8_emfoR_MI (https://www.youtube.com/watch?v=Y8_emfoR_MI)

Most probably some bad cap or maybe some power transient damaged it at night ?  or maybe a power surge ? lightning strike somewhere along the power lines ?

Thanks
Title: Re: ATX PSU
Post by: PlainName on October 04, 2024, 06:22:33 pm
Sorry for lack of update - I found a cap with bulging top, replaced with similar (1.8F instead of 2.2F, but that's better than the 7uF the original was showing) but since I bought a replacement to get the PC running again quickly (it's my partners, and she needed to do work) I've not had a way to test it in anger.

I took a photo of the cap in-situ and removed, but neither exist on my phone now! I am sure I wasn't dreaming it...

Anyway, thanks for the ideas. I will update when I manage to test the repair. I will probably bulk replace all caps to be sure, but I wanted to determine if that particular one was the sole perpetrator of if it had a partner.
Title: Re: ATX PSU
Post by: The_Spectrum.A_idiot on October 04, 2024, 06:55:20 pm
Cool :D  Keep it up sir :D

Hopefully it will get fixed after all the caps are replaced :D