PC Power Supply with shorted 3.3V

[Askic]

Hello,

Today I discovered that PSU Chieftec BDF-750C PSu has died. Not sure when that happened since I didn't use PC for a long time. PSU is not that old, about three years, but just out of warranty.
I had some previous success in repairing different electronic devices including PSU. Until now, the problem was usually bad electrolytic capacitors after many years of operation, but this time is different. When trying to turn on the PC, fans move a little bit and then nothing. There is astable 5V SB (actually 5.13 V DC Standby voltage), but that's it.
I tried to jump start this PSU ( PS On with GND), but except for 5 V SB, no other voltage was present. I have opened the PSU and after waiting some time for the big cap to discharge made some measurements.
I have found out that there is a short on +3.3V (about 0.9 Ohm to ground, but that is mostly the leads resistance).

My plan is to remove the bigger PCB and try to desolder these orange (look at the attached picture) wires that go to the smaller PCB which lead to external connectors (PSU is modular). That way I will now whether the short is on the main PCB.

In your experience, what is the common cause of this type of failure?

Thank you!

[stj]

it's probably a rectifier diode on the heatsink shorted

[jonnyGURU]

The +3.3V is on a DC to DC board. That's where you want to start.

That said, the Chieftec Proton is a very not good PSU. Double forward, passive rectification... I personally wouldn't bother. It was e-waste when it was brand new.

Not that Chieftec doesn't offer some decent models (the Polaris comes to mind as a decent Chieftec model), but the one you have has a track record of being terrible.

[CapLeaker]

as always:

Upload some straight shot, high resolution pictures from top and bottom of the PSU using the attachment function. This particular PSU wasn't much good to begin with, but lets see some carnage!

[Askic]

Thank you guys for your replies.
Thing is very weird. I have disassembled everything and started chasing for short, could not find it, then again, I measured +3.3 V against the ground and I had 1K+, so short was gone. I assembled everything back and now it is working correctly. I will test it as much as I can.
I have carefully inspected everything looking for damaged insulation on wires, or some conductive parts that could be responsible for shorting, but none could be found (except for dust, but even that, not very much).

I do have pics with higher resolution, but right now, I don't think there is a point to upload them.

I guess I'll need to wait and see how it will behave.
Once again, thank you for your replies.

[jonnyGURU]

Thank you guys for your replies.
Thing is very weird. I have disassembled everything and started chasing for short, could not find it, then again, I measured +3.3 V against the ground and I had 1K+, so short was gone. I assembled everything back and now it is working correctly. I will test it as much as I can.
I have carefully inspected everything looking for damaged insulation on wires, or some conductive parts that could be responsible for shorting, but none could be found (except for dust, but even that, not very much).

I do have pics with higher resolution, but right now, I don't think there is a point to upload them.

I guess I'll need to wait and see how it will behave.
Once again, thank you for your replies.

Something simple? Pinched wire? One has to remember on PSUs like these is that everything is common. 95% of the time, SCP only works if the short is from + to ground. So it a +3.3V works one day and not the next, one has to look at the cables/connectors.

[stj]

i start with a brush, incase there is any conductive dust on the board or tiny solder-balls from shit manufacturing.