power supply sometimes works

The supply may require some minimum load on one or all outputs to function. mike

it behaves the same, load or no load, sometimes it works but its pure luck

Check your heat sink & the heat tranfer cream, it could due to poor heat tranfer to the heat sink, i have this problum also.

Startup resistors gone high in value?

"kip" wrote:

It`s probably going to be a failing electrolytic in the mains side of the chopper circuit - I dont have a diagram but I`d expect it to be in the region of between 1 and 10 uf. Be aware that there are dangerous voltages around there, maybe even when it`s unplugged.

Ron

I have uploaded hires (1Mb each) photos here:

could you tell me which one capacitor is most likely to be the cause?

Pull then all and change them if you dont have an ESR Meter.

It would be my guess that it`s one of the little orangey ones with the black stripe under the silver heatsink, The type visible in pic 0011, right on the edge of the board. Also look for one similar near the chopper transistor - That`ll be the one on the black heatsink I reckon.

You`d really need to check all the electrolytics with an esr meter to be sure. First off I'd get all that crap out of there if I were you, and remember that there might be a charge stored in those 200 volt smoothers.

Ron

Serious question: Have you tried replacing the switch?

ok thanks all, I was going to clean it thoroughly but since electrolytics can leak I thought experienced users might see signs of leakage if not cleaned, I was also hoping it might be the switch, but after checking with ohmmeter it works ok.

err, what exactly is esr meter? My voltmeter can check capacitance (but I need to desloder them and put in special place for checking probably because of cable capacitance, right?) and it can see if capacitors are shorted.

I can check resistance between various points, if that could be of any help for solving the problem?

Why don't you just replace the filter caps and end your misery.

OK, kip, but which ones ARE filter caps? Please have a look at photos and tell me..

Ok, I'll start replacing them all. But before I try finding them, could you tell me what does '4700/16 V1' on capacitor mean? what is the capacity and voltage ? (

Thats a 4700/16 Volts

kip

and 4700 is 4700 microfarads?

yep

They can leak, but usually they fail without any visible signs. That wave of caps made with bad electrolyte did tend to bulge and leak though.