On Sun, Apr 29, 2018 at 4:19 PM, Jeffrey Birt <[email protected]> wrote: > Hello, > > > > I got a Model 100 a while ago and just got it out to do some serious > troubleshooting. After reading what I could find online I removed the NiCad > battery (bad) and replaced C82, C85, C49-50-54-55 as they had all started to > leak. The extent of the leakage was small and no visible damage other than a > small path of silkscreen coming loose as I cleaned it up. > > > > I now have all three supply voltages from the power supply. When turned on I > get a solid black LCD and a brief click from the speaker. I checked that the > processor is getting a clock and all the address/data lines are changing > states. The solid black LCD would indicate, based on previous experience, > that the LCD drivers were not initialized. I looked for PA1, etc. signals > from the 81C55 and found they were not changing state. The two signals that > looked odd on the 81C55 were the lack of /CE and IO/M changing states. I > followed the /CE back though to M16 and found that it too made use of IO/M > which was not changing states. > Did you try the ctrl-break reset? If so, I would first try to read the ROM externally to make sure it's not corrupted, then leave only 8K of known good RAM, and if IO/M is still stuck, that means the 80C85 is faulty.
Frank
