Power Supply Repair Guide ??

[Luigi]

Due to the fact that we get more and more non-working switching power supplies I'd like to try and repair at least some of them. The errors are different: no 5V or 12V output, humming, etc.

Are there any repair/test guides available?

I'm speaking of such PSUs:

[grantspain]

because these are so cheap to buy no one usually bothers,depending on whether it blows the on board fuse or not points towards the problem
usually faults on these are bridge rectifiers,diodes,caps and power ic's/transistors
if its a case of missing voltage then just trace back the output

[Luigi]

because these are so cheap to buy no one usually bothers,depending on whether it blows the on board fuse or not points towards the problem
usually faults on these are bridge rectifiers,diodes,caps and power ic's/transistors
if its a case of missing voltage then just trace back the output

I did not realize that all folks here are millionaires

A working PSU costs 40-50€ (here in Germany). We have at least 8 non-working units. If I could make 1 working out of two non-working I would be very happy


Concerning the lack of power...you are right. I should be able to just re-trace from the output point ....thanks for this little hint

[grantspain]

i pay about 30 euro's for mine,where are you buying yours from?suzo?

[SirPeale]

Bad caps are often a cause.  I'd start there.

[Luigi]

Bad caps are often a cause.  I'd start there.

What makes me asking: how can I test a cap if it's ok or not ?   Do I have to unsolder it for testing or not? You will notice that my electronic abilities are not that good


@grantspain: A german dealer has them for 39€. Even 30€ is too much to throw them all away. We have 3 Quadros in our collection. Each can hold 4 Jamma-PCBs and each PCB is served by a separate PSU.....I think now you understand why I want to repair our supplies

[modessitt]

how can I test a cap if it's ok or not ?   Do I have to unsolder it for testing or not?

If you have a meter, it may have a cap tester on it.  Unsolder the cap and insert into your meter, setting it for capacitance (usually a C) and the next setting above your cap's rating.  If you get a short or open, it's probably bad.  If you get a value that climbs steadily, it's probably good.

You can eyeball the big caps to see if the tops look like they are bulging or cracked.  Sometimes just rubbing the top of them with your finger will pick up some oily residue that stinks.  This usually means that cap should me changed because it's blown or is thinking about it.  Smaller caps aren't as noticeable, unfortunately.

If you think a different part is blown, you can sometimes find your trouble area by looking at the back side of the board for discolorations like black or brown marks caused by heat.  While some parts do heat up naturally (hence the heat sinks) this can give you a starting point for testing parts.

[Ken Layton]

http://randyfromm.com/amusements/techdept/    is a very good place to learn. Check out the power supply repair podcasts.

[Luigi]

how can I test a cap if it's ok or not ?   Do I have to unsolder it for testing or not?

..... because it's blown or is thinking about it. 

Nice


Thanks for your hints. I'll take a lok at those casts.

I hope to get some experience about that stuff and (with a little help from the experts around) I will write a little tutorial then