Help needed in debugging a circuit with JK flipflop

Thread Starter

stragulus

Joined Feb 9, 2016
10
After a long hiatus I finally got some courage to look at this thing again. I now have a nice benchtop scope, so I could at least rule out some extra variables. Turns out my initial suspicion of something holding /DOIT (Q pin 9) high was true, except I failed to properly trace the traces and missed E4 being connected (another flip-flop). This one was the culprit. With that one out of circuit, the circuitry works as expected and characters are now stored and printed onscreen. It's not the end of the story for this terminal as it has more issues, but at least the basic stuff now works.
 
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