Re: Troubleshooting Seasonic M12II Evo 750W

Unfortunately, my repair was short-lived. At first the PSU would lose 5vsb when switched on, but it would resume working normally after switching it off, waiting around a minute and switching it back on (I'm assuming some kind of protection kicks in here).
After a couple of days it just kept losing 5vsb every time, just like before.
The replacement diode is still good, though.
I'll try replacing the startup caps, but overall I'm out of ideas for now. There's nothing else physically damaged like that diode I missed be...

Re: Troubleshooting Seasonic M12II Evo 750W

Thanks for posting. As per your advice, I soldered an LL4148 MELF diode and - good news! The power supply turns on now. All that's left now is to test it with higher load.

Interestingly enough, when I first hooked it onto a motherboard, the 5vsb LED turned on and then immediately off, making me think that the repair was unsuccessful. After I disconnected the PSU from the motherboard and jumped PSON to ground the PSU turned on. After that it started working normally with the motherboard.

I got this broken power supply at an auction a few months ago and I've been making occasional attempts to fix it since.
The lightbulb test revealed that the primary side was charging the main cap properly (one brief flash when turning the PSU on). None of the main rails on the secondary were shorted to ground.
The problem - when turning the main PSU switch on it would drop the 5Vsb line to 0 (it goes from 5 to 0V when measured). The power supply wouldn't start when bridging PSON to ground. Every now and then when turning the switch on it would actually have the 5Vsb rail on but...

Re: New Members - please post your introductions here

Hey everyone, I've been lurking in this forum for a bit now. I started repairing computer components as a hobby a few months ago. Just reading through the threads here has already been of tremendous help and I learned quite a bit.