Search found 208 matches

by stephen_usher
08 Jun 2019 23:09
Forum: HARDWARE
Topic: Resurrecting an MTX500.
Replies: 226
Views: 24656

Re: Resurrecting an MTX500.

Well, the address decoding's broken. If I have ROM B or ROM C in circuit at the same time as the Diag ROM then it doesn't start up. The EEPROMs test fine in the writer so it's the machine. I feel that there's probably a full set of chip replacements in order... but not until September. It's going ba...
by stephen_usher
08 Jun 2019 20:37
Forum: HARDWARE
Topic: Resurrecting an MTX500.
Replies: 226
Views: 24656

Re: Resurrecting an MTX500.

Actually the CPU is fine. After pulling all the memory and fitting the Diag ROM I at least have something on the screen! Video RAM is fine, as is the VDP. The chips running the keyboard seem to be dead, quite possibly both the buffer and the other chip. One thing to note with the Diag ROM. If the RA...
by stephen_usher
08 Jun 2019 19:18
Forum: HARDWARE
Topic: Resurrecting an MTX500.
Replies: 226
Views: 24656

Re: Resurrecting an MTX500.

Looking on the bright side, at least you have most of the ICs in sockets now :) On the not so bright side, if you really have applied that voltage to all of the chips, there’s a good chance that all,of the VRAMs (as a minimum) will be blitzed, they are particularly sensitive to voltage levels and p...
by stephen_usher
08 Jun 2019 18:29
Forum: HARDWARE
Topic: Resurrecting an MTX500.
Replies: 226
Views: 24656

Re: Resurrecting an MTX500.

Damn and blast! Back to square one due to tiredness and stupidity. I noticed that the case was getting hot around the heatsink area, so I decided to test the current flow. So I reconfigured my multimeter to the 20A mode by plugging the probe in the other port. I checked the 5V line current draw and ...
by stephen_usher
08 Jun 2019 16:32
Forum: HARDWARE
Topic: Resurrecting an MTX500.
Replies: 226
Views: 24656

Re: Resurrecting an MTX500.

OK, I'm back to almost instantly crashing in CP/M. This image is what I manage to get when typing 'dir' just before the machine locks up: IMG_1476.jpg Something is either heat sensitive or it's a capacitor which heals itself if the machine is left turned off but starts to degrade as soon as it's pow...
by stephen_usher
08 Jun 2019 16:12
Forum: HARDWARE
Topic: Resurrecting an MTX500.
Replies: 226
Views: 24656

Re: Resurrecting an MTX500.

Bother! Spoke too soon. After half an hour it started playing up again.
by stephen_usher
08 Jun 2019 15:53
Forum: HARDWARE
Topic: Resurrecting an MTX500.
Replies: 226
Views: 24656

Re: Resurrecting an MTX500.

Due to stuff not arriving for other machines I've had time today to get the machine out and replace the TIP....

And it seems to be working OK!

CP/M doesn't crash all the time (though reading the filesystem can sometimes fail). :D

Methinks we have another fully operational Memotech!
by stephen_usher
08 Jun 2019 14:09
Forum: GENERAL DISCUSSIONS
Topic: MTX 512 (debugging thread)
Replies: 48
Views: 6985

Re: MTX 512 (debugging thread)

I'd also be concerned about the damaged traces around the 10D/10E area.
by stephen_usher
08 Jun 2019 12:57
Forum: GENERAL DISCUSSIONS
Topic: MTX 512 (debugging thread)
Replies: 48
Views: 6985

Re: MTX 512 (debugging thread)

There is a reason that Memotech used those RAM chips, trying to make them work as 64k is Ill advised and we don’t know if the machine ever worked in its current configuration. You could do away with the bodge board and use a proper PAL/GAL, but I think that a better plan is to return the machine to...
by stephen_usher
08 Jun 2019 12:16
Forum: GENERAL DISCUSSIONS
Topic: MTX 512 (debugging thread)
Replies: 48
Views: 6985

Re: MTX 512 (debugging thread)

As you have an engineer friend, probably the first thing to do will be to upgrade the ROM sockets to allow you to use EEPROMs: http://www.primrosebank.net/computers/mtx/repairs/rom/mtx_rom_replace.htm Then write a set of normal ROMs (you have the later three 8K ROMs) plus Martin's Diag ROM. Install ...