A1200 Power Supply popped/dead

[Blitter]

I've not used my A1200 for about 5 years. I just plugged it in, the power supply made a small pop and then I heard a small rapid clicking noise for a few seconds which then slowed to a stop.


Tried switching it on again and just the clicking could be heard so switched it off again and the clicking wound itself down again.
I checked the internal fuse with a multimeter and it appeared to be ok.

Any clues as to what's happened and how to sort it?


Is it likely to have fried my A1200? (I didn't even see the power light come on)

[Daedalus]

It would be rare that a failing PSU would take the Amiga with it, but it is possible (unlike earlier PSUs like the C64, which regularly brings C64s to silicon heaven with it). That the power light didn't come on at all would suggest that the Amiga wasn't affected so it should be fine.

That sort of failure could simply be that the PSU's time had come, but it also sounds like a failure caused by a short circuit. Is there any chance that something inside the Amiga may have been bent or moved to cause a short? If that's the case, then the Amiga killed the PSU, and not the other way around

[Blitter]

Amiga has been sat in a box since I last used it, but if the Amiga had caused the problem wouldn't the fuse in the PSU (or plug) have gone first?

Can I safely test the resistors/diodes inside the PSU? I have a multimeter but am noob and scared of electrocuting myself!

[jbilander]

What PSU model is this? Just drain the capacitors of any charge before you start poke around, you should be safe. Inspect the electrolytic caps visually if any has "popped" and start leaking. One option to repair is to replace the guts of the PSU with a new Mean Well RT-50B (and reuse the cabling). I have made some 3d-printable mounts uploaded on grabcad to fit the MW RT-50B (just search on "amiga"), then you can do like in video below + get a snug fit that holds the MW in place.

[ Show youtube player ]

[Nightshft]

When it is unplugged and the capacitors are discharged (which you also can measure with the MM) you should be quite safe.

You can measure components with the multimeter. Note that while they are in circuit, other components in parallel, can influence the reading. So to measure the true value of a suspected component you'd maybe have to unsolder and lift at least one leg.

PS: More caution is needed with CRTs. Their capacitors can hold high voltages over long periods of time so this is a different league.

[Blitter]

Originally Posted by jbilander

What PSU model is this?

It says Power Supply A600, P-no. 391029-02 on the bottom.


Visually I can't see any leaking from the capacitors, and they're not bulging.

[Daedalus]

Originally Posted by Blitter

Amiga has been sat in a box since I last used it, but if the Amiga had caused the problem wouldn't the fuse in the PSU (or plug) have gone first?

Not necessarily. The fuses in the plug and PSU (if fitted) protect the primary side, not the secondary. A dead short on the secondary side will cause components to fail, not fuses.

Can I safely test the resistors/diodes inside the PSU? I have a multimeter but am noob and scared of electrocuting myself!

As others have said, yep. But this isn't the sort of failure usually associated with resistor or capacitor failure (though it is possible). Check the resistance between ground and the different power rails on the Amiga. They will vary, but the 5V rail should start at a few dozen ohms and gradually increase as the capacitors charge. The + and -12V rails should do something similar, but will tend to be higher. If any of them stay below, say 10 ohms, or if they have a resistance between each other of less than 10 ohms, then there might be something to look at there.