Pac-Man Issue

Peale

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This Pac-Man has this screen. Any jumping off points? Plus, as an added bonus, Pac and Ghosts disappear during game play.
 

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I had this on one of my repair log entries: Pin 4 of the middle 74LS157 was supposed to connect to pin 2 of the middle 74LS257 on both sides of the connector that plugs into the main board. Removed a blob of solder that was an attempted repair and soldered in a jumper to finish the repair.

It was a VRAM Addresser problem.

Look for cut/gouged traces, bent pins, bad socket on the main board, etc...
 
Nice call on the 157s. When I first got the board I noted that the legs of most the chips on the VRAM board were corroded. I was concerned that might affect its performace - so I removed them all and socketed them. It was more an excuse to practice with my new desoldering tool than anything.

I placed each chip back where I got it from, so when I fired it back up afterward there was no change in symptoms.

I verified continuity from board to board, and it was okay. No gouges anywhere.

Swapped two of the 157s for each other with no change, swapped another two, and /presto/ there was still garbage on the top and bottom, but it was completely different. I took a 157 from a junk board, popped it in, and all the problems disappeared, including the disappearing Pac-Man and Ghost Monsters.

Thank you all!
 
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