jj_alukkas
Newbie level 6
Fixing a PC ATX SMPS
Hi all,
I have a 400W ATX smps lying around which I'm trying to repair to run an old motherboard. Got it from my cousin with the fuse blown off. On checking, I found that both 13007 switching transistors had blown out of which one was shorting the circuit. The bridge, capacitors and rest were fine, so replaced both 13007's along with the fuse and tested all caps on the whole board and all components on the primary side. Connected a 35w automotive bulb as load onto the +5v and on switching it on, the supply was fine and gives steady +5 on the VSB line. But when I short the PS_on to GND to switch the supply on, the smps starts making a arcing like sound as if something had a loose connection. It was clearly from the transformer, so disconnected and de-soldered it out and checked, but it seems to be fine. Tried resoldering everything and powered it up again but the same arcing sound. The smps fan tries to start, but moves a bit and stops. Checked the voltage on the lines, everything was low at around 2v on the 5v lines.. After 10 secs, the NTC blew up and the supply died again. The opto seems fine when tested out of the circuit.
I am sure of a shorted semiconductor somewhere on the secondary but could anyone point me where to start? The circuit has SB1040, STPS201 rectifiers and something called STPR10 on the secondary. The PWM is a TL494 and controller is a PJ339 but I have no Idea how to check these. No other diodes or resistors seems to be blown visually. I hope the 35W bulb wont be a problem.
Thanks a lot!
Hi all,
I have a 400W ATX smps lying around which I'm trying to repair to run an old motherboard. Got it from my cousin with the fuse blown off. On checking, I found that both 13007 switching transistors had blown out of which one was shorting the circuit. The bridge, capacitors and rest were fine, so replaced both 13007's along with the fuse and tested all caps on the whole board and all components on the primary side. Connected a 35w automotive bulb as load onto the +5v and on switching it on, the supply was fine and gives steady +5 on the VSB line. But when I short the PS_on to GND to switch the supply on, the smps starts making a arcing like sound as if something had a loose connection. It was clearly from the transformer, so disconnected and de-soldered it out and checked, but it seems to be fine. Tried resoldering everything and powered it up again but the same arcing sound. The smps fan tries to start, but moves a bit and stops. Checked the voltage on the lines, everything was low at around 2v on the 5v lines.. After 10 secs, the NTC blew up and the supply died again. The opto seems fine when tested out of the circuit.
I am sure of a shorted semiconductor somewhere on the secondary but could anyone point me where to start? The circuit has SB1040, STPS201 rectifiers and something called STPR10 on the secondary. The PWM is a TL494 and controller is a PJ339 but I have no Idea how to check these. No other diodes or resistors seems to be blown visually. I hope the 35W bulb wont be a problem.
Thanks a lot!
Therre is a specific category for repai tips. Moved to Service Manuals, Requests, Repair Tips [alexan_e]
Last edited: