The LCD now works but I am not sure why. All the signals/voltages seemed to be present at the LCD connector and the LCD worked fine on another M100. I went back though the power supply section carefully de-soldering, pulling components to look for corrosion, and res-soldering and then washed that area of the PCB with alcohol. I can only guess there was some bit of conductive debris somewhere causing the LCD to not function properly.
I was chatting with group member B4 Me100 via email and he mentioned that in the boot process the M100 reads back the status of the LCD so the fact that it was booting and letting me type in beep meant that the LCD was responding. Since the screen was blank and not black that meant the driver ships were being initialized properly which would have seemed to point to the D/I line not switching into data mode to allow writing pixel data. I’m glad it works but would love to know why it did not. I’m also very close to having one of B4 Me100's M100/T102 diagnostic harness board sets completed! Waiting on a few connectors I forgot to order with the rest of the parts. Jeff Birt From: M100 <[email protected]> On Behalf Of Jeffrey Birt Sent: Monday, July 6, 2020 8:52 AM To: [email protected] Subject: Re: [M100] M100 switching power supply troubleshooting After contemplating things overnight, I pulled the battery and T18 this morning. I pulled T18 by mistake as I thought it was T20. I was after T20 as it is responsible to the auto power down and it will also work without the memory battery. This did no good. I then realized had not pulled T20 so I then pulled it and magically had +5V and -5V back! I checked T20 and it was fine and I ohmed at all the connections to it and they were fine. I soldered it back in and still had +5/-5. I can only guess there must have been a piece of schmaltz across the leads I could not see. I did a hard reset and it will beep when ‘beep’ is typed in, but the display is blank. But at least it is progress. BTW, you can get small DC-DC converters with a remote off input. Jeff Birt From: M100 <[email protected] <mailto:[email protected]> > On Behalf Of Josh Malone Sent: Monday, July 6, 2020 8:04 AM To: [email protected] <mailto:[email protected]> Cc: Model 100 Discussion <[email protected] <mailto:[email protected]> > Subject: Re: [M100] M100 switching power supply troubleshooting 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
