Thanks Jeff B, & Bert P. I will review the note from Ian, and in the meantime did recheck the CPU (using a logic probe and my BK Precision multimeter).
Crystal Oscillators - X1 = 32.76 khz - X2 = 4.916 mhz M19/CPU - #1 = constant signal - #2 = 4.916 mhz - #12-19 (AD0-7) = detect a pulse on all lines - #21-28 (A8-15) = detect a pulse on all lines - #37 (clk) = 2.458 mhz - #40 (vdd) = 4.929 v - noted activity or sorts on all other pins. >From the above it appears the CPU is active, of course without an oscilloscope (on my list to get), I can only confirm activity present - not whether good/valid. My next steps are to recheck the physical LCD cable, and then dive into the "LCD Initialization – From Ian" and see if I can identify anything there. Really appreciate the response, it has really helped encourage me onward. I'll check back with what I discover, and welcome more ideas in the interim. Cheers, Alan On Fri, Jul 17, 2020 at 12:17 PM Bert Put <b...@bellsouth.net> wrote: > 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?____ > > > > __ __ > > >
