AXP AXP-500P12P 3.3V line issue

[zunasthegreat]

Hello all

I have this PSU from a friend, it has very high 3.3V line output (3.55-3.6V) on the DMM that makes most boards buzzer beep and shut off. Once a while on some old P4 board (P5PL2) it run fine for a bit with voltage hitting ~3.4V. It started doing it after like 2h of usage.
The original caps had TUL CE branding without any other info, 2200uf 10V for 3.3V+5V. All caps are near ~3000uf with very high vloss so I swapped them with GP caps and on the 2nd round with some KY/PW, no change in high 3.3V with any cap setup. It was there with the originals too.
The 5Vsb and +12V are both fine and I use some KY/PW there as well. Nothing seems odd but I went ahead and changed the Mospec S20C40C with a SBL2040CT, voltage on dmm starts at 3.35V and quickly drops to 3V while I clip running it with just dvd and some fans. Anyone having some suggestion on how the 3.3V is so crappy ?

[zunasthegreat]

Re: AXP AXP-500P12P 3.3V line issue

Update: After some playing with the load resistor for 3.3V (50ohm) the psu worked for like ~1h on the same P5PL2 with very stable 3.3V line @ ~3.4V but at some point it switch off. The mainboard standby led is still on and the 5VSB looks fine at 5.05V, the PSU does the same 1-2sec fan spin and will switch off. It will do it on any board run for 1-2sec and then switch off. I even re-installed the old S20C40C but that made no difference. Primary caps Transistors etc look fine.

[zunasthegreat]

Re: AXP AXP-500P12P 3.3V line issue

The fix was either the TL431 or the 2SA1015 transistor, replaced one more zener nearby that seemed dodgy and PSU works fine again.