HP 9805 (HP-46 AND 81)

[vassilisprevelakis]

(09-14-2019 02:08 PM)aj04062 Wrote:  Symptom:
The hammer that hits the rotating drum is malfunctioning on the digit to the right of the decimal. It is hitting the drum far too many times and essentially turns the output on the paper into a black box (probably hits every digit on the drum)

I have another printer unit and I’ve determined it is not the printer , the issue is somewhere in the calculator as this alternate printer does the same thing.

I need some ideas from some EE’s on why it’s signally this hammer to hit way too many times or why it lost the ability to correctly time the hammer hit

Thanks
Adam

The arrangement to drive the printer on all three models are 4001 CMOS driver chips (essentially quad 2-input NOR gates) driving transistors. In my case one of the 4001s was flaky
so one column did not print and another would print every now and then.

Changing the 4001 fixed the problem.

You just need to check what goes into the 4001 and compare it with what comes out. If they do not match then the 4001 is the culprit.

I'd check the transistor as well, just in case.

**vp

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