price: 22 CAD platforms: C64
check all of the ICs, ROMs and I/O ports (I/O port checks requires a Full Test Harness) on your C64.
The 586220 Diagnostic Cartridge was used by Commodore themselves to test every unit as it came off the assembly line.
Thanks to various contributors over the years, the 586220 has been updated to the 586220++ and provides proper Kernal detection and SX-64 support.
Pair this with the Full Test Harness to identify any issues you might be having with your C64.
Find out more / buy at: https://retrorewind.ca/c64-diag