Sure, you can use C64 diagnostic cartridges on your 128, but all you are really checking are the components that the C64 mode uses. What about all the other RAM or the other ICs that are only used in 128 mode?

Now you can check all of the ICs, ROMs and I/O ports (I/O port checks requires a Full Test Harness) on your C128 in 128 mode mode.

The 785260 Diagnostic Cartridge was used by Commodore themselves to test every unit as it came off the assembly line.

Pair this with our Full Test Harness and a C128 Keyboard Dongle and you will be well on your way to identifying any issues you might be having with your C128.

We also offer a C64 Diag and a Diag 264 cartridge for the Commodore 64 family and the Commodore C16/+4 family respectively.

Full manual and support can be found on our Support Wiki.