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HP Forum Archive 09

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HP-12c double entries?
Message #1 Posted by JackStafford on 22 Nov 2002, 1:25 a.m.

My HP-12c sometimes creates double entrys when I press the 6 and 4 keys. The problem seems to be occuring at an increasing rate. Is this a common problem? Is there a fix or maybe keyboard cleaning I could do?



Re: HP-12c double entries?
Message #2 Posted by Nick on 22 Nov 2002, 1:30 a.m.,
in response to message #1 by JackStafford

My first suggestion is to check the batteries.

Re: HP-12c double entries?
Message #3 Posted by Tom Sherman on 22 Nov 2002, 8:25 a.m.,
in response to message #1 by JackStafford


I think this is probably a common problem among recent 12C's. I returned two Chinese units to Staples before getting one that had proper key action, and I returned a Malaysian unit to WalMart before getting a good one. The problems were in various keys, numbers and functions.

Maybe someone can suggest a fix. I hope so.


Re: HP-12c double entries? - A suggestion
Message #4 Posted by Vieira, Luiz C. (Brazil) on 22 Nov 2002, 11:22 a.m.,
in response to message #3 by Tom Sherman


I faced this sort of problem in many new and earlier HP's, mostly those used in severe environment (open field, dusty atmosphere, etc.).

Each key has it's own contact-plate, and under this plate there is a small, metal-covered hole. This is the way dust gets in, and also the way we pull it out.

I'm gonna try to find the original posts (it's gonna be a bit hard, but...) where a description is made. Anyway, I'll try to describe it my way; please, correct me if I use incorrect terms.

Open the calculator (four screws, each one under each rubber feet) and locate the hole for the repeating key. Allow a small amount of micro-oil (WD 40, White Lub or any better product) to get inside the hole under the key. Thin (very thin) metal wire can be carefully inserted in these holes while the key is released. After that, gently press the key and pull the thin wire out slowly, as you release and press the key again. This will remove any sort of dust.

I myself prefer the painting brush's coats (Gee, is this correct?). It cleans the same way and does not smear the conductive metal.

If it is too much confusing, Ill try to explain in another way.


Re: HP-12c double entries?
Message #5 Posted by Jack Stafford on 24 Nov 2002, 2:02 a.m.,
in response to message #1 by JackStafford

Thanks everyone,

I'll start with new batteries (the batteries are about 15 years old) and then the wire thingy, and report results back.

:) Jack

Re: HP-12c double entries? - Please, read!
Message #6 Posted by Vieira, Luiz C. (Brazil) on 24 Nov 2002, 9:33 a.m.,
in response to message #5 by Jack Stafford


I forgot to mention one very important thin about opening the calculator.

Upper and lower halves of the calculator's case have aluminum bezels, and these bezels compose an ESD protection. This ESD protection work only when electrical field is null inside the calculator, what is accomplished when these bezels have the same electrical potential, i.e., they must be electrically connected with each other.

Two tinny, small, little springs inside the calculator's case do this job. When you remove the screws and open the case, do not turn keyboard's half upside down before removing these tiny little springs. One is located closer to the batteries compartment and the other is in the middle of the keyboard, right side. Remove them carefully and place them in a safe place, so you can put them back when locking the calculator's case again. Note that one of the springs, the one closer to the batteries compartment, is a bit bigger than the other.


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