Powerbook Duo 210 - Won't boot, hissing

[novastar]

I've acquired a Powerbook Duo 210 for my collection.

It ran perfectly for about 3 minutes from the original Apple power supply when without warning, my house fusebox tripped. I think the PSU had shorted but when I tried it a second time, the Duo bonged followed by a blank screen and a loud hissing sound at which point I disconnected it all immediately. There was no battery in the unit.

Any idea what's up? There 7 large caps on the motherboard but none of them looked to have leaked. I can't see any obvious blown components or damage. Could it be a power regulator? I've replaced many bad caps at this point but I've never encountered a hiss. It's definitely not coming from the speaker either.

If the PSU had blown, how was it able to boot the machine a second time? And why would the startup check succeed?

Any help appreciated.

 

[uxwbill]

It is very likely that the power adapter has failed. In general terms, nothing you do on the output side of that power supply (including shorting the output) should cause any fuse to blow under normal circumstances. The power supply controller should just shut down.

I'll take a guess that perhaps you lost one of the "X", "Y" capacitors (if present) or even the primary filter capacitor in the power supply. It might still happen to start up, but it won't operate correctly, may fail in a truly spectacular fashion and might well take the computer with it when that happens. The output would be extremely noisy and unstable, which might explain the hissing noise you heard.

 

[novastar]

The hissing came from the Duo, not the PSU.

Yes I think the PSU failed catastrophically. I'm hoping that replacing the caps and getting a new PSU will fix this. If there was a surge or a voltage inversion, it would have destroyed one or more of the caps. I'm not an electronic engineer but there's nothing else on the board that could make a hissing noise like that other than a blown cap AFAIK.

There's no fuse that I could see and the machine wouldn't chime if a fuse had blown. Nor are there any bulged diodes or other surface components. If it were a transistor it would simply be dead.

It's encouraging that the machine still chimed. It's the same symptoms I've seen with the PB100; the machine would chime but not boot indicating that there was enough power to run the hardware check but no more. The HD doesn't spin up either, just like the PB100 prior to recapping.

Strangely, the PSU is rated at 24V which is a LOT for 68030, passive greyscale powerbook. All of my 1xx series machines (including the 180 and Duo based 150) are rated for 7.5v and happily run off the same adaptor. Why does it need so much juice? The Duo also uses a strange phono plug style adaptor similar to the later iBooks which is going to be harder to replace.