pacman pcb no characters

LyonsArcade

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Hey guys, I have a pacman board it comes up and works but there's no characters on the screen, you can play it and watch the dots disappear but no ghosts and no pacman

I know all the roms are good, I've switched out all the socketed ram with known good ones still no go, any ideas?

Thanks!
 
Should apply...

NoPac.jpg
 
A logic probe would help a lot here. Especially one with audio so you can hear the slight differences between those signals.
 
I had the same thing happen on a board I had, it ended up being on the VRAM Addresser daughter board.
Lawnmower man's site said this.......

"Plays, No Characters in Maze or intro Screen. Dots visible & disappear as eaten.

(rare case) Dead 74LS157 at U5 of V-Ram Addresser (rare case)."

I replaced one of the 3 74LS157's, it fixed my problem then started doing the same thing again after a few hours. I replaced all 3, and haven't a problem in over a year!

I'll look at my board tomorrow and confirm that those were in fact the chips I replaced
 
Hi Guys,

Sorry to hijack your thread... But is somebody able to either post or pm me a hi-res picture (closeup) of the 285 SyncBus and 284 VRAM Daughter boards... both sides please

Cheers
Gitch
 
Just google the lawnmower mans site. Plenty of pics on there. If you still can't find what you are looking for let me know, I'll be glad to snap a couple shots......
 
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