Hi Matt Thanks. I have found similar issue with the LCD cable on the ends, corrected and carefully reinserted. I will take another look, and redo continuity from connector to connector.
If I can find a flat ribbon with the correct specs, I’ll also try to order a replacement. Here’s to hoping I missed something with the cable! Alan On Fri, Jul 17, 2020 at 11:52 Matthew Stock <st...@csgeeks.org> wrote: > Hi Alan, > > I was working through a similar issue recently. Fortunately, I had access > to a logic analyzer and was able to confirm that the CPU was operating > properly, and even where in the ROM it was looping. Once I was able to > determine it was waiting for the LCD status to change, I rechecked the > cable and found that several pins on the cable end that slide into the LCD > connector had delaminated and folded over. I was able to smooth them out > and insert the cable and the LCD behaved after that. > > I know you mentioned that you already checked the cable, but it might be > worth checking the ends and/or run a continuity test from the soldered > connector pins on the motherboard and the LCD board to be certain you have > electrical connectivity all the way through. > > Matt > > > On Fri, Jul 17, 2020 at 2:15 PM perhaps...@gmail.com <perhaps...@gmail.com> > wrote: > >> 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? >>> >>> >>> >>
