Resurrecting an MTX500.

About original Memotech hardware.
stephen_usher
Posts: 205
Joined: 27 Nov 2016 19:58

Re: Resurrecting an MTX500.

Post by stephen_usher » 01 Sep 2019 12:22

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.)

stephen_usher
Posts: 205
Joined: 27 Nov 2016 19:58

Re: Resurrecting an MTX500.

Post by stephen_usher » 01 Sep 2019 12:36

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.

Martin A
Posts: 417
Joined: 09 Nov 2013 21:03

Re: Resurrecting an MTX500.

Post by Martin A » 01 Sep 2019 12:55

Did the TIP ever get replaced ??

User avatar
1024MAK
Posts: 568
Joined: 24 Dec 2012 03:01
Location: Looking forward to summer, in Somerset, UK

Re: Resurrecting an MTX500.

Post by 1024MAK » 01 Sep 2019 12:58

Well, at least you have got back to where you were :?

Mark

stephen_usher
Posts: 205
Joined: 27 Nov 2016 19:58

Re: Resurrecting an MTX500.

Post by stephen_usher » 01 Sep 2019 13:49

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.

stephen_usher
Posts: 205
Joined: 27 Nov 2016 19:58

Re: Resurrecting an MTX500.

Post by stephen_usher » 01 Sep 2019 15:53

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?
Last edited by stephen_usher on 01 Sep 2019 16:40, edited 1 time in total.

stephen_usher
Posts: 205
Joined: 27 Nov 2016 19:58

Re: Resurrecting an MTX500.

Post by stephen_usher » 01 Sep 2019 16:40

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.

Post Reply