Z80 ERROR
Causes
The 68k didn't receive a reply to command $01 from the Z80 in time. The Z80 doesn't test the SM1 ROM, its RAM nor the YM2610 but if any of those components are bad, they can prevent the Z80 from being able to reply which will then cause the error.
Repair suggestions
On MV1F boards, this error seems common due to trace cuts caused by a leaking battery. A few wires can solve the problem.
- Check Z80 +5V supply, reset and clock signals
- Check connectivity to Z80 work RAM
- Check connectivity to SM1 ROM or cartridge's M1 ROM
- Check NEO-D0 Z80 control lines
- Check Z80 data bus at NEO-C1
- ...
Note: Replacement SMT Z80s can be found in some Ti calculators :)
MV1C
The MV1B board displays this error when no cart inserted because it has no SM1 ROM. This is normal.