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HP-80 display problem.
10-22-2021, 11:49 PM
Post: #3
RE: HP-80 display problem.
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.
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Messages In This Thread
HP-80 display problem. - jlw - 10-22-2021, 06:15 AM
RE: HP-80 display problem. - teenix - 10-22-2021, 08:13 AM
RE: HP-80 display problem. - jlw - 10-22-2021 11:49 PM
RE: HP-80 display problem. - teenix - 10-23-2021, 12:51 AM
RE: HP-80 display problem. - jlw - 10-23-2021, 06:04 AM

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