Computer power supply repair attempt

[scolen3]

So after reading a couple books, and reading up, I decided I would try to repair something useful. This would give me somewhere to start, a friend had this XBlade power supply that died on him. I do not know exactly how it died, but apparently it just stopped working one day.

I decided to pop it open and take a look, it had been sitting for over a year and a half, so I am not worried about any residual charge left over. I could not find anything too interesting, but did notice a couple things. There is a 1000uf 10v capacitor that appears to be bulging from the top. Also, but less interesting, the area around this green device labeled 10S050M, perhaps a capacitor, is discolored slightly darker than the rest of the board. This is both on the top and bottom side of the board. I am going to go through and diode test the transistors perhaps later today, and will see if anything is up there.

Help on this repair project would be greatly appreciated, there must be a way to fix it, and someone here must know how to help.

 

[Nigel Goodwin]

Bulging electrolytics is a sure sign of failure, and a VERY common fault.

Replacing any bulging ones may cure it, but sometimes it causes further damage elsewhere.

 

[HarveyH42]

Computer power supplies aren't usually that expensive to replace, least not compared to the motherboard, hard drive, or pretty much anything else that depends on it... If it's faulty, is it worth the risk bringing it back to life? Something caused the capacitor to fail, so most likely not the only fault, could be other problems after the capacitor failed as well. True, it's educational, maybe just for fun, but is it worth risking the poor computer's life on?

 

[Nigel Goodwin]

Something caused the capacitor to fail

Been a cheap crap capacitor caused it to fail - there are huge numbers of sub-standard electrolytics in use. Capxon are one of the most common failures, and are of unbelievably low quality and reliability.

As I said above, the capacitor failing 'may' cause further damage, it's not the other way round.

 

[mdanh2002]

You don't need to hook it up to a motherboard in order to test it your repair has been successful. If it's an ATX power supply, short the purple pin on the ATX connector to ground and the power supply should turn on.

 

[3lectrokid]

Ive always used the green wire to start the PSU

 

[mneary]

You don't need to hook it up to a motherboard in order to test it your repair has been successful. If it's an ATX power supply, short the purple pin on the ATX connector to ground and the power supply should turn on.

Purple (pin 9 on ATX) is +5V standby. Should NOT be shorted to ground.

 

[mdanh2002]

Purple (pin 9 on ATX) is +5V standby. Should NOT be shorted to ground.

My mistake, should be green wire. I know it's bad but I always power on the supply without the motherboard that way.

 

[Reloadron]

As a beginning this link leads to a pretty good basic drawing of a 200 watt ATX Form Factor PSU. Granted we don't see many 200 watt units anymore, however, the design concept pretty much remains the same for higher rated units. Additionally, note some of the theory of operation in the link. Useful stuff!

Next, and as was mentioned, the main PSU to Motherboard connector should contain a single green wire. That wire floats (using a pullup) with 5 V Stand By power. Placing that line low should start the PSU. Before even doing that, you want to check for the presence of 5 Volt standby power. Lacking 5 volt SB the thing will never start.

One forum member here I know has poked around and repaired a faulty ATX PSU is MrAl. He has "been there & done that".

Generally, as was mentioned, failures in these things is frequently caused by capacitors failing. When checking caps be sure to pay attention to the ESR values.

A note of caution. Be careful with the thing connected to mains and open case. Look at the link I posted and pay attention to where mains power comes in. Especially note C5 and C6 with their associated bleeder resistors. Those puppies can place a hurt on you!

Ron