My desktop PC PSU just stopped working all of a sudden

Thread Starter

rambomhtri

Joined Nov 9, 2015
481
Hello, my main desktop has a Corsair CS750M PSU and I was yesterday navigating in Chrome while suddenly my PC shut down. I instantly thought "oh, no, a blackout...", but it was not a blackout but my PC's fault. I started to think what the heck could have happened. I was not willing to accept a component had failed, since I normally buy "expensive" items from well known brands. At the same time I was hoping it was the cheapest component possible: PSU, better than the motherboard or CPU.

I discarded the PSU because those things are rock solid, even generic Chinese free (with the purchase of a PC case) PSUs last forever, let alone an expensive well designed and built PSU from a solid brand. However, after a few test I was starting to think it really was the PSU. And effectively it was, no spark, no weird smoke, nothing, it just simply stopped working. I swapped it by another one and the PC turned on nice. Thank God.

Then I spent the next 30 minutes fighting with my BIOS and cables and connections because the PC was booting into the BIOS always, never to Windows. Indeed it was not giving me the option to boot from a storage device because none were recognized. After assuming all my SSDs and HDDs were fried due to the PSU, I was about to test them separately thinking the worst scenario possible and... I notice... these drives were connected to the 4 pin power cable of the... broken unplugged PSU instead of the new one (I plugged the cables in the open and they were all flying around, and forgot to swap the storage drives power ones). My look had no price. I stared at the unplugged PSU for 1 min wondering how dumb one can be, no matter how expert in the matter he is.

The PSU is 10 years old but it's a Gold certificated Corsair PSU, really well built and kind of expensive for a PSU (compared to a generic $30 PSU).

1654122698446.png

I am starting this thread to basically ask how such a straight forward component like a PSU, without moving parts except the fan, and electrically and electronically well designed, robust and solid, can fail like that, suddenly. I think what triggers me the most is that the PSU I'm using temporarily is a Chinese generic one older than the expensive Corsair that just failed. And, now that you are here, what do you think probably failed.

Of course I'm an user of this forum meaning I opened the PSU entirely to check if I could repair it, but everything looked just fine, all caps, all cables, all solderings, all relay, chips... So I really don't have much hope. Besides that, PSUs or chargers (laptop, etc...) are the only devices I kind of "fear" because it's the only component that has shocked me in the past: a freaking charged capacitor was to blame. God I do hate large big caps... I just hate the idea of a component that can hurt or surprise you even disconnected from the outlet. Diabolical invention.
 

nsaspook

Joined Aug 27, 2009
9,993
Most PSU failures I've seen are stress related while operating in the normal reliability curve of equipment age. Blackouts, brownouts, dirty or dead fans are all killers. Power conditioning/online UPS power with good cool clean air are the standard countermeasures.
 

Reloadron

Joined Jan 15, 2015
6,712
My and my wife's systems run 24/7 and over the years I have replaced a few power supplies. I always keep at least one spare so if one fails we are back online. A few friend's were failures attributed to the above.
in the normal reliability curve of equipment age. Blackouts, brownouts, dirty or dead fans are all killers
With an emphasis on fans. :)

Ron
 

Reloadron

Joined Jan 15, 2015
6,712
That's why I buy used server class machines for 24/7 duty.
https://instock901.com/hp-proliant
Nice link. I have built a few workstations. Yes, what we have never gets shut down. Even power outages, the UPS units kick in but only for about a min till the generator is online. TV Cable, phones routers and everything on UPS. I hate dark and cold. :) Actually I really have no use for a workstation since retiring but my last one is still sitting here working when I want it.

Ron
 

Ramussons

Joined May 3, 2013
1,278
Hello, my main desktop has a Corsair CS750M PSU and I was yesterday navigating in Chrome while suddenly my PC shut down. I instantly thought "oh, no, a blackout...", but it was not a blackout but my PC's fault. I started to think what the heck could have happened. I was not willing to accept a component had failed, since I normally buy "expensive" items from well known brands. At the same time I was hoping it was the cheapest component possible: PSU, better than the motherboard or CPU.

I discarded the PSU because those things are rock solid, even generic Chinese free (with the purchase of a PC case) PSUs last forever, let alone an expensive well designed and built PSU from a solid brand. However, after a few test I was starting to think it really was the PSU. And effectively it was, no spark, no weird smoke, nothing, it just simply stopped working. I swapped it by another one and the PC turned on nice. Thank God.

Then I spent the next 30 minutes fighting with my BIOS and cables and connections because the PC was booting into the BIOS always, never to Windows. Indeed it was not giving me the option to boot from a storage device because none were recognized. After assuming all my SSDs and HDDs were fried due to the PSU, I was about to test them separately thinking the worst scenario possible and... I notice... these drives were connected to the 4 pin power cable of the... broken unplugged PSU instead of the new one (I plugged the cables in the open and they were all flying around, and forgot to swap the storage drives power ones). My look had no price. I stared at the unplugged PSU for 1 min wondering how dumb one can be, no matter how expert in the matter he is.

The PSU is 10 years old but it's a Gold certificated Corsair PSU, really well built and kind of expensive for a PSU (compared to a generic $30 PSU).

View attachment 268557

I am starting this thread to basically ask how such a straight forward component like a PSU, without moving parts except the fan, and electrically and electronically well designed, robust and solid, can fail like that, suddenly. I think what triggers me the most is that the PSU I'm using temporarily is a Chinese generic one older than the expensive Corsair that just failed. And, now that you are here, what do you think probably failed.

Of course I'm an user of this forum meaning I opened the PSU entirely to check if I could repair it, but everything looked just fine, all caps, all cables, all solderings, all relay, chips... So I really don't have much hope. Besides that, PSUs or chargers (laptop, etc...) are the only devices I kind of "fear" because it's the only component that has shocked me in the past: a freaking charged capacitor was to blame. God I do hate large big caps... I just hate the idea of a component that can hurt or surprise you even disconnected from the outlet. Diabolical invention.
Open the PSU, do a cleaning of the Fan, Heatsinks.
If it still does not work, check for a blown main fuse.
If the main fuse is blown, check the main filter caps for damage, shorted switching transistors, .....
Simply replacing a blown fuse is very likely to give you another.
 

Thread Starter

rambomhtri

Joined Nov 9, 2015
481
Open the PSU, do a cleaning of the Fan, Heatsinks.
If it still does not work, check for a blown main fuse.
If the main fuse is blown, check the main filter caps for damage, shorted switching transistors, .....
Simply replacing a blown fuse is very likely to give you another.
I already opened it and I could not find anything wrong. A fuse... the problem with the PSU is that is so freaking crowded of componentes, I have to desolder some stuff to take a clean look at everything :(
 

Reloadron

Joined Jan 15, 2015
6,712
I already opened it and I could not find anything wrong. A fuse... the problem with the PSU is that is so freaking crowded of componentes, I have to desolder some stuff to take a clean look at everything :(
If you are intent on troubleshooting this thing start with the basics. Place it on a bench and look for the 5.0 volt SB (Stand By) voltage. Next look at the PS_ON only green wire on a 20 or 24 pin main connector. Short PS_ON to ground, any black wire. Most newer PSUs do not need a load. What does that do? Personally I just trash the things but you can take a few steps.

Ron
 
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