Help for fixing PSU

[everell]

Re: Help for fixing PSU

Replace C503 4.7 uF capacitor. It is the "critical" capacitor in this power supply.

What is brand and model number of this power supply? What is measurement of 5VSB circuit? If Vcc to the TL494 is 30 volts, I would expect the 5vsb to be about 10 volts.

[hkqq2010]

Re: Help for fixing PSU

The 12v seems to not be regulated.

Try replacing C503, C506, C507 and C508.

Maybe get a few pictures too?

The primary caps could be bad too, causing the hum sound.

Thanks for your reply.

I am sorry that I made a terrible mistake. I found that it is caused by offload of 12V. After I re-connected TL494, exciting transistors and some other components, it abruptly drop to 2.5V. After replacing C506, it back to 11V. But it still can't provide any output. I will continue to try to fix it when I am available.

About hum sound and primary caps, I will keep them in mind. When I try it next time, I will deal with it.

Many thanks again.

[ben7]

Re: Help for fixing PSU

The 12v seems to not be regulated.

Try replacing C503, C506, C507 and C508.

Maybe get a few pictures too?

The primary caps could be bad too, causing the hum sound.

[hkqq2010]

Re: Help for fixing PSU

Some info I want to add, it is an atx PSU, and there is "hum" noise from T3.

[hkqq2010]

Hi guys,

I have a dead PSU with no output at all and fuse burnt. After replacing power transistors and some resistors, the +5Vsb is back now. But I found the Vcc of PWM TL494 is over +30V which should be around +12V. Here is the diagram of the related circuit.



Is there anyone could give me some hints which part I should check it first?

Many thanks in advance.