Search found 573 matches

by 1024MAK
05 May 2019 20:31
Forum: NEW HARDWARE
Topic: System test rom/Board
Replies: 26
Views: 2992

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: 18159

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: 18159

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: 18159

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
by 1024MAK
28 Apr 2019 19:51
Forum: HARDWARE
Topic: Resurrecting an MTX500.
Replies: 226
Views: 18159

Re: Resurrecting an MTX500.

The ‘sparks’ and arcing can also be caused by cracked / fractured tracks and dry joints. Does any of the non-functional circuitry have missing +5V supplies, or are lacking good 0V/ground connections? The requirements for a Z80 to run are: +5V and 0V power /RESET having gone from low to high A valid ...
by 1024MAK
22 Apr 2019 01:16
Forum: NEW HARDWARE
Topic: System test rom/Board
Replies: 26
Views: 2992

Re: System test rom/Board

8-) 👍

Mark
by 1024MAK
18 Apr 2019 23:33
Forum: NEW HARDWARE
Topic: System test rom/Board
Replies: 26
Views: 2992

Re: System test rom/Board

Wow! That was quick work Martin :shock:

Excellent progress and excellent work 8-) :D 👏

Mark
by 1024MAK
13 Apr 2019 23:53
Forum: HARDWARE
Topic: Resurrecting an MTX500.
Replies: 226
Views: 18159

Re: Resurrecting an MTX500.

Assuming it was the +5V that was shorted out, the most likely item in the power supply section of the board that will have been damaged is the current boost transistor, Q4 (TIP2955). That’s the large power device on the heatsink. Also check it’s the associated resistor (R62, 10 ohms) and the 7805 vo...
by 1024MAK
12 Apr 2019 15:14
Forum: HARDWARE
Topic: Resurrecting an MTX500.
Replies: 226
Views: 18159

Re: Resurrecting an MTX500.

There should be enough room at the rear of the case, next to the video board riser, possibly above the video RAM to fit a board with a PLCC socket. Other than the data lines from 4000-05/06 ROM A socket it shouldn't need many from the other two should it? Data and address lines are all the same for...
by 1024MAK
12 Apr 2019 15:10
Forum: HARDWARE
Topic: Resurrecting an MTX500.
Replies: 226
Views: 18159

Re: Resurrecting an MTX500.

Also you will find this old post of mine useful. Although please don’t reply in that thread until I have sorted out the missing photos in the last post...

Mark