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Museum of the Game® & International Arcade Museum® Forums
So I thought I'd try this new subforum out with a bronze age repair-help question. I skimmed through the "First!"-thread started by andrewb and tried to see if there were any decisions or suggestions on what kinds of posts belong here and felt like there are no clear guidelines yet. So let's try with a repair-help question and see how it goes
Anyway, I have a Super Bug that is not booting. It feels like the sync signals are off. Attached is a pic from my logic analyzer showing the signals 1H, 2H, 4H, 8H and 16H. The first four of them seem to be ok, but 16H seems to be ticking at roughly the same frequency as 1H. Should it not be twice as long as 8H? I tried using a different probe for the logic analyzer just to rule out a bad probe, no change.
The signals 1H through 16H are developed by the 74161 at N5 (see attached schematic screenshot). I have replaced this IC but 16H is still showing like in the picture. I tested the 7474 at P5 in-circuit with a HP logic comparator and it tested fine. I also made some measures on N6 (which develops signals 32H through 256H) and it seems these signals are off too. I thought I'd start by focusing on the 16H signal from N5 though.
Anyone having any thoughts on where to go next? Any components that would be the "usual suspects"?