Apple /// Power Supply

The other thing I use _a lot_ is a ringing tester, for detecting shorted turns in transformers, etc. A single shorted turn in the chopper transformer will cause all sorts of problems, best to find it before you blow another expensive chopper transistor. Wehn I was sorting out the Boschert 2-stage PSU in my PERQ 1 (it blew up in a big way, all 3 chopper transistors chorted, 723 regualtor chip blown apart, a couple of resistors burnt, afew small signal transistors gone too (one was just 3 wires sticking out of the PCB), and even a couple of tracks melted), I managed to borrow a nice, regulated, current-limited HV PSU. I could apply 300V to the input of the chopper circuit, knwoing I'd set the limit low enough to protect the new components if/when things went wrong. Problem is, such supplies are not cheap, and I've not managed to get one myself yet. But don't forget the humble (filament) light bulb. It makes in ideal current limiter. Connect it in series with the HT+ line from the smains smoothing capacitors to the chopper. It'll at least prevent burnt PCB tracks if things go wrong again. -tony