Badcaps Forums

Badcaps Forums (
-   Troubleshooting Power Supplies and Power Supply Design (
-   -   AXP AXP-500P12P 3.3V line issue (

zunasthegreat 11-07-2021 09:15 AM

AXP AXP-500P12P 3.3V line issue
3 Attachment(s)
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 11-08-2021 09:12 AM

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 12-27-2021 03:41 PM

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.

All times are GMT -6. The time now is 07:27 AM.

Powered by vBulletin ®
Copyright ©2000 - 2022, Jelsoft Enterprises Ltd.