Hi John,
I had a look back on your original topic with your PC85 Coreboard "Upgrading a Microbee PC85 to a PC85b and adding extra Game ROMs" and you originally had a problem with the ROM I which disappeared. So I suspect you have a mechanical issue around there associated with ROM I.
I have not reread the whole post, but did you change the 25 way headers on the PC85 Coreboard? If so then as someone says you could have a compatibility issue with the pins causing poor contact on either of these headers.
Unless you made alterations to the MB8328 Coreboard and the other (working) MB1248-6 board to get them running, then changing from a MB1632 or a MB1732 across to the MB8328 should work fine, as both are SRAM boards.
The big difference between them is the use of !PORT A signal. The older 32K boards didn't use this and it is critical to the correct selection of the ROM PAKs. The other big difference is the power drawn by by the MB8328 is a lot higher and if there is some high resistance in the connections, this will show up more in the PC85 configuration. Are you using the same power input you were when it was working fine before? I do know you made up an adapter to drop the power down to 10V, was this after you had the system running before? If so try taking the power in back to 12V and give that a try.
Hopefully that will give you a few ideas to try out.
Ernest
I had a look back on your original topic with your PC85 Coreboard "Upgrading a Microbee PC85 to a PC85b and adding extra Game ROMs" and you originally had a problem with the ROM I which disappeared. So I suspect you have a mechanical issue around there associated with ROM I.
I have not reread the whole post, but did you change the 25 way headers on the PC85 Coreboard? If so then as someone says you could have a compatibility issue with the pins causing poor contact on either of these headers.
Unless you made alterations to the MB8328 Coreboard and the other (working) MB1248-6 board to get them running, then changing from a MB1632 or a MB1732 across to the MB8328 should work fine, as both are SRAM boards.
The big difference between them is the use of !PORT A signal. The older 32K boards didn't use this and it is critical to the correct selection of the ROM PAKs. The other big difference is the power drawn by by the MB8328 is a lot higher and if there is some high resistance in the connections, this will show up more in the PC85 configuration. Are you using the same power input you were when it was working fine before? I do know you made up an adapter to drop the power down to 10V, was this after you had the system running before? If so try taking the power in back to 12V and give that a try.
Hopefully that will give you a few ideas to try out.
Ernest