Recently purchased a non working mr do! Bootleg pcb from a member, he said it booted to coloured lines on the screen.
Here it is on my work bench.
It appeared in nice condition with no trace damage.
Inspecting the components I noticed the 19.6mhz crystal was missing and according to the schematics this frequency is responsible for the horizontal and vertical counters as as for the video circuits.There is a capacitor which looks like it's leg is ripped out and importantly I noticed the z80 cpu installed is 2.5mhz which should be 4mhz,anyways let's see what happens when powered on.
Yep that's definitely got coloured lines, ok next I put in a new capacitor,crystal and a z80a cpu (4mhz).
Powered on and....
ok good news is we have a proper sync and rgb but the code is not running, i did a romident on the 4 program roms d1,d 2,d3,d4.
All passed except d1 which failed the romident, burned another one with the correct file and powered on...
Cool 😎 mr do is alive but all the sprites are corrupted and all over the place, I suspected the sprite rams and looking at the pcb they have been socketed ,also these ones installed seem to be slow at 250ns,I scoped the outputs of these 2 srams but looked ok.I put in 2 srams with 150ns .
Powered on and...
Mr do! Lives
Game is now working and all controls good,another one saved 👌
Here it is on my work bench.
It appeared in nice condition with no trace damage.
Inspecting the components I noticed the 19.6mhz crystal was missing and according to the schematics this frequency is responsible for the horizontal and vertical counters as as for the video circuits.There is a capacitor which looks like it's leg is ripped out and importantly I noticed the z80 cpu installed is 2.5mhz which should be 4mhz,anyways let's see what happens when powered on.
Yep that's definitely got coloured lines, ok next I put in a new capacitor,crystal and a z80a cpu (4mhz).
Powered on and....
ok good news is we have a proper sync and rgb but the code is not running, i did a romident on the 4 program roms d1,d 2,d3,d4.All passed except d1 which failed the romident, burned another one with the correct file and powered on...
Cool 😎 mr do is alive but all the sprites are corrupted and all over the place, I suspected the sprite rams and looking at the pcb they have been socketed ,also these ones installed seem to be slow at 250ns,I scoped the outputs of these 2 srams but looked ok.I put in 2 srams with 150ns .
Powered on and...
Mr do! Lives
Game is now working and all controls good,another one saved 👌
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