There's a good possibility that the thermistor used to slow the current inrush during power up has left this earth. They work by heating up as their resistance drops.
If they're original, the heating/cooling cycles will cook them over a 40 year lifetime. I've had them fall apart just by touching them. The good news is that they're still available from Mac! I believe they're a CL-90 thermistor, if you've got a supplier close by, though.
To confirm this is your problem pull the bottom cover and you'll see a component about the size of a US 25 cent piece with 2 wires welded to its sides. If this is still intact, then look at the power switch and see if you can find some burned spots. Arcing as you saw would generally leave some hints.
Just be careful if you plug it in with the bottom off and with it plugged in. The part of the circuit I'm talking about will have the full 120vAC available to bite you.
Hope that helps.
Cheers,
David
If they're original, the heating/cooling cycles will cook them over a 40 year lifetime. I've had them fall apart just by touching them. The good news is that they're still available from Mac! I believe they're a CL-90 thermistor, if you've got a supplier close by, though.
To confirm this is your problem pull the bottom cover and you'll see a component about the size of a US 25 cent piece with 2 wires welded to its sides. If this is still intact, then look at the power switch and see if you can find some burned spots. Arcing as you saw would generally leave some hints.
Just be careful if you plug it in with the bottom off and with it plugged in. The part of the circuit I'm talking about will have the full 120vAC available to bite you.
Hope that helps.
Cheers,
David