Seasonic X660 not turning on when PC is in sleep mode

[joekajoeka]

Hello,
I have a Seasonic X660 from 2011 a very quiet and reliable PSU it worked great but in 2023 started that it wont turn on when the PC is sleeping, if I switch fast the power switch on the PSU than it would switch on and also the PC wakes up from the sleep.
If the PC is shut down normally than also the PSU starts normally every time.
(I checked the PSU on another PC with the same result for sure the PSU is faulty)
Has somebody a clue what is wrong in the PSU? has somebody repaired this fault for this exact PSU? I would like to repair this PSU.
Thank You!

[momaka]

Hmmm, that's an interesting fault.
The only difference (to the PSU) when the system is in soft-off (turned Off) state and sleep (standby) is perhaps current draw on the 5VSB should be higher.

Try this test:
Put a load on the PSU (like an HDD or two, or possibly more stuff, like a few 12V auto bulbs on the 12V rail) and try powering it on by grounding PS_ON signal. Does the PSU turn On normally? Can you do this a few times in a row both quickly after each other and spaced apart in time?
Now repeat the above test, but this time, after you power on the PSU, put a load on the 5VSB rail - preferably something heavier that can draw at least 1 Amp from it. Now remove bridge between PS_ON and ground to make the main rails of the PSU turn Off. After this, pull PS_ON to ground again to see if it will start. What I'm trying to determine here is if the PSU can start when the 5VSB is loaded. All of the caps in the PSU appear to be reputable Japanese brands, so I don't think they would be the issue here. If you do have an ESR meter, though, perhaps it may be worthwhile to pull out and check the caps on the 5VSB output filter (the brown KZH caps close to the smaller transformer.)

[joekajoeka]

Hy, thank you for your suggestions,

I tried your first suggestion nothing on the 5VSB rail, the PSU started every time.
Then I tried you second suggestion to put something on the 5VSB rail I only had a 12V bulb I think 5W, I put it on the 5VSB the light was dim but it emitted light and the PSU started every time again! (maybe the light bulb is not enough?)

[harp]

Monitor 5vsb, what is voltage on green wire while is going to start and while is not start, is there 5v that drop to 0v?
If I am you, I will replace all small caps in power-on ic section.
What is voltage on your computer power on soft switch also in both state?
Have you 3.3v on superio and stable 5v on mainboard?

[momaka]

I tried your first suggestion nothing on the 5VSB rail, the PSU started every time.
Then I tried you second suggestion to put something on the 5VSB rail I only had a 12V bulb I think 5W, I put it on the 5VSB the light was dim but it emitted light and the PSU started every time again! (maybe the light bulb is not enough?)

Yes, it's possible the load on the 5VSB is not enough to show if there are any issues. I think 12V 20W or higher bulb would be better (2x 20W might be enough to put 2 Amps on the 5VSB.)

If you don't have any other bulbs to test, try what harp suggested below \/\/

Monitor 5vsb, what is voltage on green wire while is going to start and while is not start, is there 5v that drop to 0v?

Agreed.
Basically, plug the PSU back into your computer and connect a multimeter to measure the voltage on the 5VSB line. Now put the computer in standby / sleep mode and see what the 5VSB is. Is it still a solid 5V? (+/- 5%... i.e. it can be as low as 4.75V and as high as 5.25V. Anything out side of that is out of spec.)
If the 5VSB is good from the above test, do the same with the PS_ON pin: measure the voltage on this pin when the computer is turned On, then measure it when you put the computer to sleep / standby. Record what values you get for this (and for the 5VSB from the above test) and post the results here. Perhaps this would identify the issue with the PSU.

If I am you, I will replace all small caps in power-on ic section.

Looking at the pictures of this unit, all of the small caps look to be from reliable Japanese brands and are like reliable series too.
So I suspect the caps probably won't be the issue here.