Search found 569 matches

by 1024MAK
11 May 2019 01:43
Forum: HARDWARE
Topic: Resurrecting an MTX500.
Replies: 226
Views: 15512

Re: Resurrecting an MTX500.

8k ROM decode for Z80 CPU using a single 74xx138
8k ROM decode for Z80 CPU using a single 74xx138
8k ROM decode for Z80 CPU using a single 74xx138
8k ROM decode for Z80 CPU using a single 74xx138.png (37.21 KiB) Viewed 666 times
Mark
by 1024MAK
11 May 2019 00:52
Forum: HARDWARE
Topic: Resurrecting an MTX500.
Replies: 226
Views: 15512

Re: Resurrecting an MTX500.

8k ROM decode for Z80 CPU using a single 74xx32 8k ROM decode for Z80 CPU using a single 74xx32.png While you were taking measurements, I drew this in case it helps. It only decodes the one 8k ROM. So use it in addition to the GAL/PAL and replace the ROM CS with the output of this circuit (use a tes...
by 1024MAK
10 May 2019 23:48
Forum: HARDWARE
Topic: Resurrecting an MTX500.
Replies: 226
Views: 15512

Re: Resurrecting an MTX500.

What is the state of the other inputs to the GAL/PAL (6A)?

Mark
by 1024MAK
10 May 2019 22:49
Forum: HARDWARE
Topic: Resurrecting an MTX500.
Replies: 226
Views: 15512

Re: Resurrecting an MTX500.

You mean this book...
Cover of Z80 Applications by James W. Coffron.
Cover of Z80 Applications by James W. Coffron.
BE125876-8869-47D0-9583-E39C5E593510.jpeg (280.34 KiB) Viewed 711 times
Mark
by 1024MAK
10 May 2019 00:15
Forum: HARDWARE
Topic: Resurrecting an MTX500.
Replies: 226
Views: 15512

Re: Resurrecting an MTX500.

I’ve always found Phil at Retroleum to be quick, if he has an item in stock.

Maybe he had an extended bank holiday weekend...

Mark
by 1024MAK
06 May 2019 22:02
Forum: HARDWARE
Topic: Resurrecting an MTX500.
Replies: 226
Views: 15512

Re: Resurrecting an MTX500.

Never mind that, my brain is still trying to work out how Stephen got a cable to go inside the front of his ‘scope. Look, you can see it through the screen! :lol:

Mark
by 1024MAK
05 May 2019 20:31
Forum: NEW HARDWARE
Topic: System test rom/Board
Replies: 26
Views: 2573

Re: System test rom/Board

Excellent work

ImageImageImage

Mark
by 1024MAK
02 May 2019 21:29
Forum: HARDWARE
Topic: Resurrecting an MTX500.
Replies: 226
Views: 15512

Re: Resurrecting an MTX500.

Without either doing the same to one of mine, or working out an approximation from the schematic, it’s hard to say for certain. However, turn that figure around using ohms law: 5V / 300 ohms = 16.67mA This sounds reasonable to me. If you have a multimeter that has a current range, put it in series (...
by 1024MAK
28 Apr 2019 23:24
Forum: HARDWARE
Topic: Resurrecting an MTX500.
Replies: 226
Views: 15512

Re: Resurrecting an MTX500.

If you have multiple chips all connected to the same line that have died, especially if some only have inputs to this line, that indicates that the line has experienced a severe over voltage or a negative voltage. A short circuit to 0V / GND or to the +5V rail will not harm or destroy most chips whe...
by 1024MAK
28 Apr 2019 19:52
Forum: HARDWARE
Topic: Resurrecting an MTX500.
Replies: 226
Views: 15512

Re: Resurrecting an MTX500.

stephen_usher wrote:
28 Apr 2019 19:49
Definitely the correct voltages to the Z80.

However I've just noticed that chips 7C and &d are scorchingly hot!
That’s not good :(

Mark