Muel
Well-known member
Partially working Robotron MPU Board...almost there!
So I've been trying to bring back to life: a Williams "C" board from a Robotron.
It was dead giving a 1-3-1 error and it wasn't the RAM chips.
I replaced ICs 3D and 3E (both 74153) and the board came to life - no 1-3-1 error and now posts a "0"....Woohoo!!
So now that the board lives, I've discovered another problem: it won't hold vertical (can't adjust out on a known working monitor) and the horizontal is shifted to the right 50%.
The decoder ROMs (ROM 6 at 3C & ROM 4 at 3G) are working fine as I pulled them from a known working board.
Thinking that it might be something with the sync, I replaced ICs 3A (7411), 4A (7486) and 6C (7474) and no change whatsoever.
I can see video on the screen - it goes thru the rug pattern, goes to the High Score screen and when the screen tries to refresh to go to the attract screen, it re-boots - back to the rug pattern, then to the scores (this may be a separate issue from the vert & horiz video problem)
ROM board is known working when paired with another MPU board.
Any idea what IC that I should be looking at from here??
Thanks,
-Muel
So I've been trying to bring back to life: a Williams "C" board from a Robotron.
It was dead giving a 1-3-1 error and it wasn't the RAM chips.
I replaced ICs 3D and 3E (both 74153) and the board came to life - no 1-3-1 error and now posts a "0"....Woohoo!!
So now that the board lives, I've discovered another problem: it won't hold vertical (can't adjust out on a known working monitor) and the horizontal is shifted to the right 50%.
The decoder ROMs (ROM 6 at 3C & ROM 4 at 3G) are working fine as I pulled them from a known working board.
Thinking that it might be something with the sync, I replaced ICs 3A (7411), 4A (7486) and 6C (7474) and no change whatsoever.
I can see video on the screen - it goes thru the rug pattern, goes to the High Score screen and when the screen tries to refresh to go to the attract screen, it re-boots - back to the rug pattern, then to the scores (this may be a separate issue from the vert & horiz video problem)
ROM board is known working when paired with another MPU board.
Any idea what IC that I should be looking at from here??
Thanks,
-Muel

