Strange Power Supply Behaviour

[Robbie]

Normally if a power supply behaves strangely you'd probably get a replacement, well in this case i replaced all the capacitors and still have the same problem so i wonder if anyone can diagnose the problem.

Basically,
I turn the power supply in my A2000 on in the usual way - using the switch at the back.

Secondly, nothing happens, you can leave it for 5 seconds, then turn it off ..and it's only when you turn it off that it appears to come to life, spinning the fan and lighting the amiga's power LED briefly (about one second). Then it goes off again, but switch it back on, and it'll stay on until you next switch it off, operating perfectly.

So, given that all the capacitors inside were replaced, does this point to some kind of faulty protection circuit?

Thanks!

[ElPolloDiabl]

Could a capacitor be in backwards?

[Robbie]

I don't think so, because its only developed this symptom over time, originally it worked perfectly.

[Zardoz]

might check the bridge rectifier or diodes., also the high voltage transistors.

[rkidd7952]

I'd start by establishing that the switch itself is good.  Put the machine on a power strip, fiddle with the PSU until it's in the good state, then switch power on the power strip and see if you can provoke the same symptom.  If the symptom goes away when switching using the power strip, suspect the switch on the PSU.

Robert

[Amiwest]

If the power strip test does not find the problem: I would with power supply cold & no cover and not starting use a heat gun to see if heating different components will start it. TechTopics 20 has a schematic of a A2000 power supply but with Amiga it might not be for the one you have. I have had the thermal start up resistors ( not Amiga ) to cause intermittent start up problems. (THR! or THR2 on A2000).
http://www.bombjack.org/commodore/commodore/TechTopics_20.pdf

[gertsy]

I'd start by establishing that the switch itself is good.  Put the machine on a power strip, fiddle with the PSU until it's in the good state, then switch power on the power strip and see if you can provoke the same symptom.  If the symptom goes away when switching using the power strip, suspect the switch on the PSU.

Robert

+1