computer power supplies..

If it's ATX, ground the PS_ON pin.

See Wikipedia for Pinout.

Regards, Michael Karcher

Not a group per se, but the BadCaps forum -

Fry's Electronics sells an inexpensive 'test box' for power supplies, but it is very limited.

PlainBill

Do you have and use an oscilloscope? Good, now you are ready to start learning this stuff. Take lessons on transistors, pulse width modulation, diodes, filters, .... You will not believe how many functions are required in a power supply if you did not read its full page of numeric specs. To fix a power supply means you understand what those specs say. Implied - how many self proclaimed computer 'experts' do not even know what a power supply does. They think it only provided voltage. Learn how complex a power supply really is and the many functions it performs.

Of course, learn of the power supply controller =96 another component that many do not even know exists.

And be damn careful with the voltages inside.

Graham

I fixed an ATX supply by replacing 2 very obviously bulged caps on the output side with ones from a scrap Mobo !

Graham

Beware. It may not regulate properly with no load on the 5 or 12 V output.

Graham

just fixed mine yesterday replaceing the low imp caps on the outputs.

just fixed mine yesterday replaceing the low imp caps on the outputs.

boblarya wrote:

No, but you're on-topic in here. You can find lots of info about ATX power supplies here:

You need to ground the power-on signal, which is the green wire. If you want to use the PSU as a bench supply, you can simply snip the green wire from the back of the ATX connector, & solder a switch between it & one of the black wires.

On every PSU I've tried it on, the fan seems to provide enough load for the voltages to be okay.

Bob Larter Inscribed thus:

A lot of the better ones have suitable loading built in ! More often the PSU wont start up if it requires a minimum load, though some will but don't regulate the output voltages properly. The regulation is done with reference to the 5v rail, so that is the one that should be loaded. Its wise to play safe and stick a load on anyway. I use a 10 ohm 10w resistor wired into a spare connector so that I can add or remove it as needed. I also have a LED wired as well so that I remember to switch off when working on an open case.

having a old boat anchor disk drive laying around to use as a dummy load helps.....

bob

That can work. I'm reaching the conclusion that the proce of caps is so low (at least here in the USA) that it is better to replace all caps with new quality caps. At one time I was using an approach similar to yours. After a while I accumulated a number of power supplies that APPEARED to work well with a dummy load, but when connected to a motherboard the result was an unstable system.

Bulging caps are a good indication that a cap has failed. Not all failed caps bulge.

PlainBill

I've heard of some where the feedback is taken as a mix of BOTH the 5V and 12V loading. No guarantees though.

I agree that 'some' load on the 5V is likely best.

Graham

Not a bad idea.

Remember the Full Height 5 1/4's ? They took about 30-40 W.

Graham

The scrap mobo was Dell and used 'name' capacitors that still looked in excellent condition ( get an ESR meter if you really need to know ), whereas the bulged caps in the PSU were classic 'no name' off- brands.

The problem I've found is that the caps they tend to use are unusually small ( or odd ) form factors. Typically tall and very small diameter. Not many stockists have them.

Absolutely. Guaranteed in fact.

Indeed. Also look for electrolyte leakage around the base. Usually a white deposit. It's corrosive too, so when replacing, clean it away.

Graham

Very typical.

Also on a Mobo, check the LV regulator caps around the CPU etc.

Graham

On Fri, 24 Apr 2009 10:06:59 +0100, Baron put finger to keyboard and composed:

I haven't repaired many AT/ATX PSUs, but IME they usually (?) regulate by sensing a weighted average of the +5V and +12V rails. This means that the +5V and +12V rails move in opposite directions.

See

- Franc Zabkar