This will be really helpful. When I was making a video a few weeks ago about using diagnostic programs I thought to myself how much easier it would have been to have a M100 diagnostic ROM that would test memory before trying to do a hard reset.
I just got notice right after your email from OSH Park that my C128 KB Dongle board would be shipping in a few days. It was designed by Sven Petersen to work with his version of the C64 harness, Commodore made the C128 harness the same except for the KB dongle and cart program. Anyhow I have a few C64 test harness PCBs left over and will be getting the C128 KB dongle soon. Would you want to swap for a M100 diagnostic PCB set? I feel a diagnostic update video coming ๐ Jeff Birt (Hey Birt on YouTube) From: M100 <[email protected]> On Behalf Of B4 Me100 Sent: Thursday, May 7, 2020 3:17 PM To: [email protected] Subject: [M100] M100/T102 diagnostic harness Just shared 3 PCBs on OSHPark for an M100/T102 diagnostic harness set that I have been using to repair a few model Tโs and keep others alive. Since I found the method to be quite beneficial I thought others might be interested. If you are familiar with the C64 diagnostic harness it is the the same concept without the 3D printed enclosures :) ROM board format 1 <https://oshpark.com/shared_projects/NzijCAoF> https://oshpark.com/shared_projects/NzijCAoF ROM board format 2 (functionally the same as format 1, allows better access to some ICs on a model 100) <https://oshpark.com/shared_projects/8B9e3uA9> https://oshpark.com/shared_projects/8B9e3uA9 Harness board <https://oshpark.com/shared_projects/Yj0oMOQx> https://oshpark.com/shared_projects/Yj0oMOQx So far I have used it to debug 2 x M100s and 1 x T102. One M100 had a corroded AD2 line on the 81C55, the other M100 had two bad RAM modules that did not show up on a BASIC ram test โ not sure why, but on cold power up the machine only showed 16K when it was loaded with 32K. The T102 was suffering corrosion problems due to a battery acid leak and had 3 different faults: bad power supply, bad keyboard buffer and badly repaired NiCd battery. All these machines were sold as โworkingโ on the well known auction site :( If anyone is interested in trying the process out I have 3 sets of blank boards (some assembly will be required) that I can drop in the mail (US only sorry), they should fit in a regular envelope. If there is sufficient interest I could look at doing the old school group buy for more board sets (probably work out to around $6-10 per set of 3 boards). You will need an EEPROM programmer to load the test firmware onto the ROM board, the XGecu Programmer TL866II PLUS works fine. I am working on a guide to help with using the boards. As it stands the firmware can run tests on all parts except the modem. It does assume that the +5v and โ5v are good, the power supply is relatively easy to debug. It also assumes that the CPU and a couple of buffers are good โ however if the tests do not run then that is a good place to start looking, there is an option to force NOP onto the data bus. A voltmeter and logic probe also compliment the harness. Testing the CAS port requires using an external audio player (eg Audacity) โ only the headers are tested and generated. The screen and keyboard tests require visual inspection of the screen and keys to be pressed respectively. As the M100 has a socketed ROM it is quite easy to remove the ROM and plug in the test ROM and then hook up a test clip to the WR- line. However for the T102 you will need to use an IC clip from the ROM board header and cut the ROM CS- track (very easy to do and repair) and attach a WR- and CS- test clip.
