I have a Sanyo MBC-775, and I've modified the CPU/Memory board with sockets for the new memory (as well as futureproofing) and the logic chips required to make it work. (It has two boards at right angles, one has the CGA video output, and ISA bus, the other one has the CPU, Memory, and one parallel port.)

I've been working months on this to upgrade the memory (thinking it was a problem with adding patch wires because the board wasn't made to accept that kind of memory), but I've come across a peculiar malfunction that may make my problem easier.

The 256-kilobit (32 kilobyte) chips I bought to upgrade another computer, my Macintosh 128k, seem to be bad, because it crashed immediately upon being turned on. A RAM tester I bought a few months ago doesn't seem to point out the faulty 256-kilobit chips. (although it does point out faulty 64-kilobit chips just fine.)

The Sanyo contains a footprint for a 139 multiplexer IC, which seems odd, if it wasn't meant to accept 640k or more of memory.

My question is, would bad memory anywhere in an IBM 5160 prevent the system from booting? (Especially in the 16k critical area, according to the Supersoft diagnostics. I can't get an image on a monitor anytime the memory is in the system.)

I feel like considering the patch wires led me on a wild goose chase, and that putting in known-working 64-kilobit and 256-kilobit chips would actually allow the system to boot and start properly.

EDIT: Whoops. I forgot 256-kilobit IS 32 kilobytes.