Before trying to swap out the SM1 (and perform desoldering on the working 1FZ), I'll have a look if i have a compatible EPROM around. Maybe I can just use a big and fast enough one, put it in a breadboard and connect the wires.
As for the Z80, I don't think it's an overclocked one: the MV-1FZ has a smd Z80 (84C00AM-6), which is rated for 6Mhz (at least that's what the datasheet says).
As for the crystal, I think I have a frequency meter somewhere, and it's surely worth a check. But given that the games run fine (without audio) I doubt the crystal is at fault.
Thanks for the ideas.
As for the Z80, I don't think it's an overclocked one: the MV-1FZ has a smd Z80 (84C00AM-6), which is rated for 6Mhz (at least that's what the datasheet says).
As for the crystal, I think I have a frequency meter somewhere, and it's surely worth a check. But given that the games run fine (without audio) I doubt the crystal is at fault.
Thanks for the ideas.