I have an M100 which has a power supply issue. If the machine has been off for a while, like several days, it will actually turn on and work ok. Once it is working, if I flip the power switch off and back on, it will not turn back on. Actually the CPU is powered and keyboard works, but display seems completely off. I know the CPU is ok because after power up I can hit enter and type BEEP <enter> and hear a beep sound.
I have traced the problem so far to some issue in the negative 5 volt supply. When the machine is not working, this rail is only about -0.4 volts. I have already replaced C82 - C86 with new caps. I have already replaced the NiCad with a new NiMH battery. I pulled up one leg of D14 and the diode tester on my meter says it’s ok (0.7 volt drop forward, infinite resistance backward). R97 gets kind of warm according to my thermal camera, about 90 F. If I disconnect the display and keyboard completely, the -5 V rail still only sits around -0.4 volts, so I don’t think the problem is the display pulling too much current. I have not yet scoped the transformer or checked any transistors yet. Any ideas where to go next on this? Thanks, Steve
