TRS-80 1 & 4 also: Help with IBM part numbers and schematics

[M4] Excellent. Incidentally, you can also boot any Model 3 OS (or self-booting disk, or...) on the Model 4. You'll have a 64*16 display, like a M3, and 48K RAM, but it does work (and was designed to work). [M1] It's been a long time since I've been inside an M1, but I remmber some of it. The PSU has a cnetre-tapped AC output used for the +12V ad -5V supplies and am unsmoothed DC output (it's another centre-tapped winding with a couple of dfodes inside the power brick) for the +5V. All smoothing is on the CPU PCB. The +12V and +5V regulator circuits use the well-known 723 chip, and are linear supplies. The -5V supply is a simple zener diode + resistor circuit. I wonder if for some unknown reason the machine suddently draws too much current from one of the supplies about 1s after reset. And that shuts the supply down, it then tires to restart onlg for the prolem to repeat. I can't think what would do that, though. But the prolem might not be in the PSU area. -tony