Hi Alan, I'm with Jeff on this one. So far you've shown that you've tested voltages, cables, even the LCD contrast pot, but you haven't really talked about the logic side. You mentioned you replaced all the RAM (even installing sockets), as well as re-capping the board, but so far I haven't seen anything to verify that the system clock is running, or that the CPU is running.
It will be hard to do this without an oscilloscope but maybe you have a frequency counter or something that you can use to verify the clock is running, and that the CPU is running? Jeff's video shows how you can check for activity on the address and data lines; without that activity literally nothing will happen on the board. Good luck. Cheers, Bert (not Jeff :-) On 7/17/20 2:07 PM, perhaps...@gmail.com wrote: > 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 > <mailto: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 > <mailto:perhaps...@gmail.com> <perhaps...@gmail.com > <mailto: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 <mailto: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 > <mailto:m100-boun...@lists.bitchin100.com>> *On Behalf Of > *perhaps...@gmail.com <mailto:perhaps...@gmail.com> > *Sent:* Friday, July 3, 2020 6:28 PM > *To:* m...@bitchin100.com <mailto: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 <mailto:bir...@soigeneris.com>> > wrote:____ > > Have you done a hard reset? Ctrl+Break+Reset button. > Have you checked adjust the screen contrast pot?____ > > __ __ >
