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My trusty Seasonics 3.3v rail has dropped to 0.24v *cry* have just replaced it but thinking it would be nice to fix this for a spare if its possible.
The PSU supposedly has a single rail, so what would I be looking for as all the voltages except for the 3.3v are fine?
TBH without circuit diagrams I am not sure that is something I would want to risk a repair on.
For starters, has the output failed such that it can't supply any meaningful current any more, or is it trying to drop 12V onto that rail and the protection circuit crowbar is pulling it down to 0.24 to save the motherboard?
Perhaps it has a DC-DC converter daughter-board in that model, in which case it could be worked on in isolation. Otherwise, poking around a live PSU with an oscilloscope in order to diagnose it just gives me the willies.
Sounds to me like the 3.3v regulator's probably gone and either the overvoltage protection is kicking in, or it's gone in such a way as it's now supplying just the reference voltage. I'd have absolutely no idea how to diagnose whether either of these assumptions were right, though.
I wouldn't go anywhere near trying to repair a PSU without a detailed circuit diagram, though. It's absolutely begging for trouble. If you can find a specification and diagrams somewhere then you've got half a chance. Alternatively, if you have the technical skills to trace the PCB and work out the exact circuits, then it might make an interesting project - but I certainly wouldn't expect to end up with a working PSU at the end of it. ;)
I assume you measured the voltage with a multimeter??
Scan have had the Seasonic S12II 330W PSU for around £24 on Today Only a few times recently.
No, just measured via bios.......had been having problems with bits of the system seemingly "dying", then checked my RAID controllers logs and saw I had been being spammed with low 3.3v messages for quite some time.....and the messages seemed to increase in frequency (guess it's been a gradual effect).
Just replaced it with a HX850 (my wallet cried) but it's been such a stable beast until now that if it was an easy fix, I would have done it for a spare. By the sounds of things though, it's not going to be too easy to diagnose. I might just ask an electrician I know to have a look before ditching it. Although I guess 5 years isn't a bad innings, it isn't great either - although it has run some pretty hefty loads on a daily basis.
When it comes to anything involving electricity; if you have to ask, don't touch it.
On a more practical note, 5 years, isn't bad like you said, more so if it's under heavy use, so write it off. The parts and tools likely needed for a repair will probably cost more than a new low wattage backup PSU and personally I wouldn't trust a refurb PSU even for a back up.
I suspect a capacitor or two might have some issues.