Look very, very, very carefully around all the electrolytic capacitors in the power supply section. You have replaced the ones known to be the worst leakers but sometimes the others do leak and most often a leaking cap will cause other problems.
I recently had to pull about 30% of the power supply section components, one t a time, from an M100 clean very well around them, ohm everything out and then reinstall the component. I never did nail this down to a particular component but this particular M100 had the worst case of 'cap leak' I have ever seen on an M100. It did a number on the PCB. Jeff Birt -----Original Message----- From: M100 <[email protected]> On Behalf Of Steve Glenner Sent: Monday, September 7, 2020 6:24 PM To: [email protected] Subject: [M100] M100 Power issue: -5 rail not starting, already replaced C82 - C86 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
