HP-80 display problem.

[jlw]

Perhaps I should put the original resistor back.
Under low battery, all decimal points light, except the one following the decimal point.
Under high battery, the c segment lights in all positions except the decimal point.
Pin 1 often has a 3kHz pulse train on it, corresponding to which digits have that segment lit.
With only 2s and a decimal point in the display, the pin 1 trace is flat, but it's not ground. It rises as the battery voltage does, and probably crosses the logic threshold and lights the c segments. (45 probably doesn't do this as much, if at all) Missing or faulty pull-down resistor? (cure-by-symptom) I don't know what logic family this is. 45 or 80 logic board on another working (for our purposes) display board, pin 1 stays at ground as the power supply is varied about a whole volt.
It seems unlikely to be a faulty display as everything works fine (=larger top end before the Cs appear) with the HP-45 logic board installed. Pin 1 still floats, but not as much.