Thanks I have re-inspected the traces around the power supply caps and it looks clean, I have also used lots of IPA and Q-tips to clean the area anyway but still have the issue. I actually do see a low resistance (from 7 ohms to a couple hundred ohms) from VEE to Ground, even with display disconnected. I am wondering what besides the display uses the -5 volt rail. I followed the VEE -5 trace around the board from the junction of R97/D14 and I see the trace meanders around and goes up under the backup battery, then joins some resistors before going onto the display connector. I unsoldered the new backup battery and scrubbed under it, removed a little solder mask but looks ok. I saw the -5 rail also goes to some resistors between the backup battery and the DB25 serial connector, and after going through some resistors it goes into M35, a 4584 Schmidt trigger chip which looks like part of the serial port circuit. I’m going to lift some of these series resistors to see if the problem is downstream toward the Schmidt trigger or serial port.
Thanks Steve > Date: Mon, 7 Sep 2020 19:00:39 -0500 > From: "Jeffrey Birt" <[email protected]> > To: <[email protected]> > Subject: Re: [M100] M100 Power issue: -5 rail not starting, already > replaced C82 - C86 > > 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
