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Strange HP-10 Printer behavior - Printable Version

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Strange HP-10 Printer behavior - aj04062 - 08-30-2011

Can anyone steer me in the right direction to correct this behavior?

At the beginning of the strip the battery was nearly dead, but the printer seemed to work fine. So I charged the batteries overnight. When I tried again, I get the solid lines across diagonally as the paper advances then across again. It doesn't stop until I turn off the calculator.

If I plug the calculator BACK IN, it works correctly. See correct prints midway.


Re: Strange HP-10 Printer behavior - Marcus von Cube, Germany - 08-30-2011

You should stop using the calculator until the issue is fixed. It looks like two segments of the print head are permanently heated which will most certainly kill them over time.

It seems to be a driver issue, not a print head issue. May be an intermittent short circuit on the board.


Re: Strange HP-10 Printer behavior - aj04062 - 08-30-2011

Ah, duly noted.

Is there anything in the two separate power supply circuits that would lead to this?




Re: Strange HP-10 Printer behavior - Marcus von Cube, Germany - 08-30-2011

I've no detailed info about the printer mechanism but here are knowledgeable people on the forum which will help you. My answer was just an interpretation of the what the picture shows.


Re: Strange HP-10 Printer behavior - aj04062 - 08-31-2011

Power Supply Schematic

Can someone help explain this circuit to me? I am a ME by training, not an EE. I am guessing that something unique to the battery circuit has failed and allowed the voltage or current to differ from the intended design, thus causing the odd behavior only when the battery is fully charged or NOT hooked to the charger.

Edited: 31 Aug 2011, 7:06 a.m.


Re: Strange HP-10 Printer behavior - Kees van der Sanden - 08-31-2011

I doubt this strange behavior is caused by the power supply circuit.
The thermal elements of the printer head take a lot of current
and i expect they will be supplied directly from the battery.
I agree with Marcus that this behavior is caused by the printer head driver circuit.


Re: Strange HP-10 Printer behavior - aj04062 - 08-31-2011

Well I don't agree about the intermittent description as I seem to able to reliably recreate the behavior.

I am going to measure some of the voltage drops with and without the power supply and see if I discover anything.


Re: Strange HP-10 Printer behavior - aj04062 - 08-31-2011

when I plug it in with the battery the printer is noticeably faster and higher pitched when it prints.

Does that help anyone help me?