Hi,

Ive got some old computer PSU and I am trying to convert it into a lab bench PSU.

When I first tried it out, Ive got signal (5V) only on green and purple wires. Then I spotted a slightly popped capacitor (one of the two large ones), so I replaced it and hoped it would solve my problem. It didn't.

When I connect green to black, I should get signal on 3V, 5V and 12V but I get nothing. Only green and purple. Which brings me to a conclusion that sth is probably wrong in the part where all the cables are. But I can not figure out what, as everything seems ok to me. Does anyone have any ideas, what I should check?

 

There are two separate switch mode supplies in there. The 5V standby supply (purple wire) which supplies the green wire. When the green wire is grounded it switches on the main supply. That main supply is faulty.

 

Short out the Green and any Black, it should kick up, if not it's repair time...

 

I guess its repair time. Im quite new to electronics and I am trying to learn sth. Would it be possible to point me in a direction where I should look for the fault? Or there isn't an easy solution and I should just give up? I should be capable of replacing a few components, the thing is I am unable to locate any, which might be faulty.

 

Take it from from me with 20yrs experience of these dogs, unless you have a circuit diagram and knowledge of switchmode psus you won't be able to fix it. You will need to search for the chip number and get information on google.

 

Ok, thanks for your advice. I will just start with sth smaller and easier.