Alive but not working

[Architect]

Also in my case the culprit was a 7420. It was IC52 (page 24). I found it by using signal IN (pin 5 of IC117, page 04) to trigger my oscilloscope (also vintage) to see what happens the moment 377 is read/written while I push CLEAR or one of the data buttons. It is not that IC52 was functionally faulty, but it negatively influenced IC40 and IC41 to push up the signals WD and WT to 1.6 V which makes them 1 in stead of 0, causing a delay-line full of 1s.

Of course I cannot run programs now because I used IC75 in its place. I'll solve that tomorrow.