I too have an M100 with weird power supply issues. I'm seriously contemplating designing a replacement M100 SMPS for cases like these. Would not be as simple as finding an OTS module though, if we want the software power control to keep working. :-/
I have had to replace the xfmr in one machine I got in for repair. I'd love to find a suitable replacement for that part as well. I haven't gone to the length of measuring a known-good one yet though. Have you tested the inductance of the xfrmr yet? -Josh On Sun, Jul 5, 2020 at 11:43 PM Jeffrey Birt <[email protected]> wrote: > Hi All, > > > > I’m working on a M100 that was desperately in need of having the > electrolytic caps replaced. That job was done, and the mess cleaned up. > That being said the power supply section is not working. At one point it > did start working briefly and was outputting a steady 5V and -5V. > > > > The memory battery is charged: VB = 3.3V > > VL ~= 5.5V all the way to Pin 4 of OT2. > > I ohmed out the +5V and -5V rails to make sure they were not shorted. > > > > Measuring across secondary of the transformer, OT2, pins 7-9 with scope > shows a blip on power on. However, T21/T22 are not oscillating. Ohming out > the transformer shows both primary and secondary seem OK. > > > > I have done the simple things like checking the diodes and transistors and > double checked that the leaking caps did not cause any broken traces. > > > > It looks like if I remove T20 I can isolate the auto power off circuitry. > I’m trying to figure out what T27 and T28 do as well as figure out what > steps to take next. > > > > Since it briefly worked it could be an intermittent short/open or perhaps > a component is right on the edge of tolerance and not letting it start to > oscillate? > > > > Open to any ideas. > > > > Thanks, > > Jeff Birt >
