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HP Forum Archive 08

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20s problem
Message #1 Posted by Nick on 6 June 2002, 4:21 p.m.

I have a hp 20s calculator that doesn't respond to the keystokes for a whole bank of keys. The Blue Shift, 4,5,6 and the X all will not work. But if I press down just below the display, and "queeze" the calculator, then I can input the keys.

All the rest of the keys work fine.

Before I make this my test calculator that I take apart, is there a fix to this?

Thank you, Nick

Re: 20s problem
Message #2 Posted by Paul Brogger on 6 June 2002, 4:58 p.m.,
in response to message #1 by Nick

The keyboard connector contacts the printed circuit board internally just below the display. The keyboard connector is 15 (I think) contacts on a flexible mylar (I think) circuit. Pressure for the connections is established by a rubbery strip laying just below the mylar. As the PCB is fastened into place, the rubber holds the mylar and PCB contacts together.

I think in some (especially aging) Pioneers, the rubber strip shrinks over time, and the keyboard traces lose contact with the PCB.

I've fixed some of these by taking them apart, removing the PCB, lifting out the rubber strip (it lies in a slot molded into the plastic face half of the case) and bolstering it with a strip of something about 1 mm thick underneath. (A rolled-up strip of celophane tape is one approach.)

Then simply replace the rubber strip (it should sit a little "higher" now), the PCB, and the case halves, and it should work fine.

Instructions on how to take apart & put together Pioneer models are to be found elsewhere on this site:

MoHPC Repairs & Batteries Pioneer Repairs

MoHPC Articles Forum -- #199: Increasing HP-42s Memory to 32K

Good Luck!

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