Robocop pcb repair

This Robocop pcb booted up but the majority of the graphics were missing with only some text and the life bar showing up. The first thing I did was try the rom board on a known good main board and it worked perfectly so I knew the issue was with the main board.

 

After ruling out all the ram and ttl I started to look at the surface mount customs, pins can often lift on these. I reflowed them all but it made no difference. It went back in the pile after that for a few months until I pulled it out again today and decided to check the only two things I hadn't already which were the two prom chips. Of course it could have been a bad custom but I like to rule everything else out before I even think about replacing those.

Comparing the outputs to the ones on a good board I found that pins 13 and 14 of 7112E prom @E17 on the bad board were stuck low.

I had two scrap data east main boards from a trade many years ago. They were scrap in every sense of the word, the previous owner took a drill to the cpus trying to remove them and cut away parts of the board trying to remove certain chips, but luckily the proms were still there.

I fitted a socket and the 'new' prom.

This restored all the missing graphics, repair complete.