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VIC-20 Diagnostics Harness and Cartridge
After finding the VIC-20 Diagnostic Software on zimmers.net, I decided to make a diagnostic harness for the VIC-20, that is as similar to my C64 Diagnostic harnes as possible. The schematics of the diagnostic harness was/is available from Ray Carlsen's website.

Unfortunately the feedback, even of the IEC Dongle are completely are completely different, so I could only keep the Cassette PCB (which has no feedbacks), the ribbin cable to the Cassette PCB and the ribbon cable to the (single) control port (Joystick Port). This results in two new PCBs and a different concept for the IEC dongle. The user port PCB is much simpler than the C64 user port PCB and just contains passive parts.

My
Super Expander II cartridge can serve as a diagnostic cartridge. Only two RAMs (IC3 and IC4) are required, which connect to /RAM1.


Diagnostics Cartridge/Super Expander II with 1kB of RAM





The software is available in two versions. Once says "VIC-20", which is the NTSC version, the other software is announcing "VC-20", which is the PAL version of the original Commodore software.

The software is pretty fast, probably due to a not very intensive RAM test. The display is scrolling while reporting the test results and a couple of test images are displayed to get an impression of the picture quality. It stops at the first bad test item and flashes, other than that, it is a infinit loop and suitable for burn-in tests.





The keyboard is not reported open, when no keyboard dongle is connect, it is reported as ok. Experimenting with interrupted feedbacks shows, that a bad keyboard VIA/circuit is reported properly.

A JiffyDOS Kernal will not pass the test, since it does not have the right checksum.

The VIC-20 Diagnostic Harness was tested fully functional. The project data will be released on my
github repositories as soon as the documentation is finished.