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The initial display seems to be a lamp test, and from that we can see that some displays do not work: the three alphanumeric ones on the left and the two on the right. The “channel” one initially did not work either but that was just a loose connection.
Focusing on the “unit” display I checked U4, a shift register for one of the digits (74ls164). pin 8 is its clock (blue) and pin 1 is its data (yellow):
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So we do seem to have data being shifted through.