Question about HP 12c Calculator

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Keyboard HP 12c

I can not work with "Zero" symbol and "+" symbol. Do you know how to fix it?

I have been running the normal test to find something wrong, but every thing seems to be fine.

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Under the rubber membrane ,touching the individual symbols (in this case zero & plus[+] there is a carbon coating (black stuff) that shorts out the two metal connectors on the board, when u press down on the keys
Open hp12c and lift up membrane away from body and see if the metal contacts[on the body] are warned, damaged or that the " black stuff " is on the membrane.
u can try a fix...........take a small piece of aluminum foil and glue it to the underside of rubber membrane where the "stuff" was.
Don't put a thick piece because the metal foil should bounce back with the membrane as u press down on the key.
Hope that helps.
I tried this once.........a small dab[ hey!!,, when I say a dab....i mean a dab....of glue. Sharpen a pencil & rub the tip across a EMERY board so that the carbon "black stuff" from the pencil falls on top of the glue. Let it set & try for 2 hrs or more.

Posted on May 14, 2008


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Posted on Jan 02, 2017


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It could be some dirt or grit in the keyboard, which a blast or two of compressed air might clear out. It could be a worn dome on the inside of the keyboard.
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No OS stated, is this windows or linux or freedos.?
This PC came with VISTA in the USA< is it still vista? or slammed with some other alien OS. (not using HP install media)

windows WHAT, must we beg ?
Testing 1,2,3, simple as falling off a log. really.
ok try something more useful
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does that work?. if yes, good, if not the OS is corrupted.
(know that corruption has endless possibles) ask.

try a real keyboard, all USB work on your LAPTOP
if that fails, then your OS is corrupted,
if that works, the USB key board, then your internal keyboard is bad, time for a new one, for sure.

Be Backed up first your DATA backed up 1st !

power on button
then quickly hammer the F11 key,
this is the HP magic F11 recovery key.
then do a full recover.
if you PC was slammed with MS disks , F11 is now dead forever.
the book books is free, we are not HP here. is HP.

your sevice manual is at HP. hot at fixya .

posted 100s of times, here, and 1million times at HP.
search much?

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HP 12C

gtabblt.gif Description gtabblt.gif Resetting the calculator using the keyboard gtabblt.gif Resetting to drain the capacitor gtabblt.gif Other solutions gtabseps.gif Description Sometimes a calculator will lock up or will not respond correctly. The calculator may require a reset for a variety of reasons. These resets will erase the memory on the calculator and restore the calculator’s defaults. For this reason, it is important to back up any critical data. Resetting the calculator using the keyboard The easiest reset is done from the keyboard. To reset the calculator, follow the procedures below in the order presented.
  1. Press ON to turn off the calculator.
  2. Press and hold [ - ] .
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  6. The calculator will reset to the default settings, and the memory will be erased.
If the above reset did not restore the calculator to normal, continue to the next section.

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