mecha
Well-known member
swap ram 21 with 31 or 11, does the error carry? I mean you could just have a bad ram, I don't know what you've tried already.
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Taking Charles' advice, the next thing I swapped out was the two 7474s on the ROM board. The graphics copying problem is vastly improved. It only started leaving copies of enemies onscreen around wave 8 or 9 and it didn't crash, so I was able to actually finish a game.
I had to swap them out with 74LS74s because it's what I had available. Do you think it would be better to replace them with 7474s instead? I socketed them in case thos might happen again.
I still get RAM error 21 when I boot the game with this ROM board, so maybe there's another problem chip to replace?
Bizarrely, according to the logic tester in my ROM burner software, both of those 7474s are good. The 7411 I just pulled tests bad however.
Maybe one of the 7474s was just bad enough to cause trouble but still let the game run?
I'm going to get non-LS versions of these chips to see if stability improves.
It's still having some problems, like (very rarely) drawing the box around enemies or putting the high score screen border around the playfield.
Bizarrely, according to the logic tester in my ROM burner software, both of those 7474s are good. The 7411 I just pulled tests bad however.
Maybe one of the 7474s was just bad enough to cause trouble but still let the game run?
I'm going to get non-LS versions of these chips to see if stability improves.
It's still having some problems, like (very rarely) drawing the box around enemies or putting the high score screen border around the playfield.
This ROM board and MPU board don't match the serial of the cabinet and the other PCBs so who knows what this poor game has been through. It was a mess when I picked it up.