This is an old post, preserved for reference.
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This is a Colecovision, or CBS Colecovision as it was in the UK. It's one I picked up a while ago, but have not got around to restoring yet. It's not the one I am going to be repairing, just setting the scene.
TURN GAME OFF -> TWPN GAOG ODD
U -> W 55 -> 57 0101 -> 0111
R -> P 52 -> 50 0010 -> 0000
N -> L 4E -> 4C 1110 -> 1100
M -> O 4D -> 4F 1101 -> 1111
E -> G 45 -> 47 0101 -> 0111
F -> D 46 -> 44 0110 -> 0100Of those bits, it was only ever bit 1 which was at fault. In these situations, it's often stuck high or low, but here it is just consistently wrong? The Colecovision has two sets of RAM, 2x2114 giving 1K main RAM, and 8x4116 giving 16K of video RAM. Looks like a video RAM fault, and each bit is handled by a single chip, Time to remove the RAM chip connected to 9928 pin RD1 (video RAM data 1) and test it.