My next challenge: Memotech MTX500.

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stephen_usher
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Re: My next challenge: Memotech MTX500.

Post by stephen_usher » Thu May 23, 2019 10:58 pm

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.
Intro retro computers since before they were retro...
ZX81->Spectrum->Memotech MTX->Sinclair QL->520STM->BBC Micro->TT030->PCs & Sun Workstations.
Added code to the MiNT kernel (still there the last time I checked) + put together MiNTOS.
Collection now with added Macs, Amigas, Suns and Acorns.

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exxos
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Re: My next challenge: Memotech MTX500.

Post by exxos » Thu May 23, 2019 11:00 pm

Could it simply be a bad trace on one of the more upper address lines which separates the upper and lower ram banks ?
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stephen_usher
Posts: 353
Joined: Mon Nov 13, 2017 7:19 pm
Location: Oxford, UK.
Contact:

Re: My next challenge: Memotech MTX500.

Post by stephen_usher » Fri May 24, 2019 6:50 am

After the weekend, when I can turn my spare bedroom back into a hobby room, I can pull all the chips and do another continuity check.
Intro retro computers since before they were retro...
ZX81->Spectrum->Memotech MTX->Sinclair QL->520STM->BBC Micro->TT030->PCs & Sun Workstations.
Added code to the MiNT kernel (still there the last time I checked) + put together MiNTOS.
Collection now with added Macs, Amigas, Suns and Acorns.

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