Quote Originally Posted by smkdan View Post
On your good MV1F you'll get a blank screen if don't have the Z80 test cart inserted and you don't hold down button D. Try again with D in P1 port held and it should get through to the end. Was this tried on both of your bad 4 slots? If the BIOS works fine in the 1F but gives CRC error in your 4 slots then the board must have an issue. My first guess would be a bad burn for CRC errors but the working 1F rules that out. If it's the same CRC value on screen everytime I think it's a lower address line from 68k to BIOS. That can easily stop the system from working completely but it's possible to get far enough to display an error like this.
Silly me, I held the D button and all tests pass on the 1F. I also tested it on another good 4 slot board I have here a tests pass, so the BIOS is good.

On the 4 slot which gives the CRC error it gives the same value on screen each time. I will investigate lower address line from 68k to BIOS

Thanks again mate.