Re: My next challenge: Memotech MTX500.
Posted: 23 May 2019 22:58
The TMS chip has its own set of RAM which is totally separate from the rest of the system. One of those chips did have a fault, which showed up as display corruption. I replaced that.
Someone wrote a diag ROM which I used to test the main RAM, which passed. It thinks that it tested the high page and that passed, but of the address decoding part of the circuit isn’t paging correctly it could actually be testing one of the lower 16K of the 64Kx1 chips.
I could do with an independent 4164 chip tester to verify this.
As for testing the memory paging. I’ll have to learn Z80 assembler as the BASIC ROM will get paged out when this memory is paged in so it can’t be accessed from BASIC. Z80 assembler seems not as easy as 68000 though.
Someone wrote a diag ROM which I used to test the main RAM, which passed. It thinks that it tested the high page and that passed, but of the address decoding part of the circuit isn’t paging correctly it could actually be testing one of the lower 16K of the 64Kx1 chips.
I could do with an independent 4164 chip tester to verify this.
As for testing the memory paging. I’ll have to learn Z80 assembler as the BASIC ROM will get paged out when this memory is paged in so it can’t be accessed from BASIC. Z80 assembler seems not as easy as 68000 though.