Thanks Jeff. I have revisited all the documented diagnostics in the service manual, and checked/re-checked all the voltages, reset circuit and LCD.
The current state is that the system has correct voltages in both power-on/memory-on and power-off/memory-on modes. The LCD works, in as much as it can be adjusted from light to dark contrast (full black screen) but displays nothing otherwise. I have checked the reset signal on the ICs, and see only one anomaly in M28 (Flip-flop) where: - Pin #10 (RESET) - Low/0v (reset button out), Low/0v (reset button in/active) - Pin #13 (Q) - 0v (reset button out), 0v (reset button in/active). Neither state shows either high or low. - I will note that since I don't have a logic chart, I'm not sure if this is normal or an anomaly. In addition, I have checked T9, T10, T11 and T25 and with the exception of T9 all show what I assume is correct behavior on the Emitter -- H/4.9v (reset out), L/0v (reset in/active). - T9 however shows L/0.3v (reset out), H/2.7v (reset in/active). - A check of all the transistors via my multimeter (diode test) shows they all appear to be OK (0.7v from B to E, and B to C). So T9's behavior might be good, but without anything to compare I don't know. I also checked the keyboard, in case it was not working and thus the <shift><ctl><break><reset> signal would never be seen -- as best as I can tell it works. I have checked/rechecked all flat cables connecting LCD + Keyboard, and they all appear to have no bad connectors or breaks along the cable (checked in various positions to ensure not an intermittent break). Additionally, I have fully charged the memory battery, turned the system off, removed the AAAs (I have no external power supply), turned memory off for 15+ mins and repowered the unit. No change in behaviour. Blind <enter> followed by typing B E E P doesn't work, and if I leave the unit powered on, power-save does not turn the unit off. If the CPU is waiting for the LCD, and stuck in a loop how do I resolve this? If it is related to M28 and T11 then I can start with replacing T11. However, I'm reluctant to replace more parts, as full recap, new X1 and X2 and D13 have not changed the behavior so far. At this point, I'm at a loss and would welcome advice - I really do want to get this fully functional. Thanks in advance. FYI I'm more than happy to talk real time with anyone offline too. Cheers, Alan On Fri, Jul 3, 2020 at 5:10 PM Jeffrey Birt <bir...@soigeneris.com> wrote: > One other thing I forgot to mention. I started a video series on general > troubleshooting methodology for vintage computers. The idea is to cover the > troubleshooting process rather than the repair of a specific computer. The > first video is about evaluation of the computer and getting yourself > started down the right path. > > > > https://www.youtube.com/playlist?list=PLegscpHOheJt_EpuPs9hfBpOJ5elRhYvw > > > > Jeff Birt > > > > *From:* M100 <m100-boun...@lists.bitchin100.com> *On Behalf Of * > perhaps...@gmail.com > *Sent:* Friday, July 3, 2020 6:28 PM > *To:* m...@bitchin100.com > *Subject:* Re: [M100] M102, Black Screen, Help! > > > > Thanks Jeff. > > > > On Fri, Jul 3, 2020 at 5:27 AM Jeffrey Birt <bir...@soigeneris.com> wrote: > > Have you done a hard reset? Ctrl+Break+Reset button. Have you checked > adjust the screen contrast pot? > > >
