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Re: Resurrecting an MTX500.

Posted: 01 Sep 2019 12:22
by stephen_usher
Well, it's September and I'm back to the MTX...

It looks like the GAL acted as a lightning rod and took all the damage. Phew!

After I replaced that I have a working machine again. If anything, for some unknown reason it seems a little more stable than it did before with CP/M running for longer and more reliably than it did before (though not as well as on my other machine).

What I might do is leave things as they are and bring the machine along to Memofest and let the whole team try to diagnose the final issues with the machine.

Anyway, the upshot is that I now have a complete set of replacement chips for the machine, excluding memory, the sound chip and that one 74LS chip which has gone out of production. (I have other memory chips but I can't guarantee that they work as I don't have a tester.)

Re: Resurrecting an MTX500.

Posted: 01 Sep 2019 12:36
by stephen_usher
Ah, no. Leaving it to warm up and it's back to its old ways again.

I wonder if it's a problem with a capacitor.

Re: Resurrecting an MTX500.

Posted: 01 Sep 2019 12:55
by Martin A
Did the TIP ever get replaced ??

Re: Resurrecting an MTX500.

Posted: 01 Sep 2019 12:58
by 1024MAK
Well, at least you have got back to where you were :?

Mark

Re: Resurrecting an MTX500.

Posted: 01 Sep 2019 13:49
by stephen_usher
Martin A wrote:
01 Sep 2019 12:55
Did the TIP ever get replaced ??
I don't believe it was in the end.

However, I've been soak testing the machine with 32K programs and it's rock solid. It's been running the port of "Comic Bakery" non-stop for almost two hours now without a hitch.

Re: Resurrecting an MTX500.

Posted: 01 Sep 2019 15:53
by stephen_usher
It looks like it must have been a memory problem that the diag ROM doesn't pick up.

I spent an hour swapping memory on one socket (fitted a sacrificial socket on top of the one on the board) and went through all the other memory chips I had, including a set of OKI 64Kb ones, and found all the chips that passed.

I installed the complete set of OKI chips and the machine seems, as far as I can tell, fully operational. No glitches. CP/M runs fine. (So, far... *crosses fingers*)

Does anyone know of a full RAM test system for the old RAM chips?

Re: Resurrecting an MTX500.

Posted: 01 Sep 2019 16:40
by stephen_usher
No more issues! It looks like it's a fully functional machine now.

(OK, the keyboard switches bounce a bit, but are getting better. To begin with most didn't work at all. Mostly fixed with switch cleaner/lubricant + working them a lot.)

I must admit that I've not tried loading a tape, but that can be left for another time.

P.S. 18:54 It's been happily running stuff all afternoon.