Question about HP 12c Calculator

2 Answers

Have an HP-12C Platinum. Recently the "6" key will not register with a normal keystroke. If you really press hard, it will register sometimes, but not reliably. Was reading another post about checking the membrane switch. How do you open the calculator, and is this what I should check?

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  • peggy331 Sep 09, 2009

    I could use more help on topics 4,5, & 6. Can't identify parts. Where is PCB boss? Thanks

  • peggy331 Sep 09, 2009

    Don't know if you got my last message. Can't identify grounding springs & PCB boss. Please advise. thanks, Peggy

  • peggy331 Sep 09, 2009

    I cannot detach the board from the front of the calculator was told to cut boss, but cannot locate.

  • peggy331 Sep 09, 2009

    Having trouble separating the "guts" from the front shell. Shell is open, no problem, but can't find the hidden attachmen. Afraid to pry too much at this point might break board. Thanks

  • peggy331 Sep 09, 2009

    No screws found. Very solidly attached to front.

  • peggy331 Sep 09, 2009

    OK, got the baby going. (whew!!) The trick is this: (maybe I should work for you guys:)) There are two rows of small (plastic) rivets which attach the board to the front of the unit. Took a pocket knife and reamed those all flush, then the board could be released. Cleaned behind the contact where the "6" is, repositioned carefully then reassembled. Self test went fine. The only boo-boo I made was to lose the tiny grounding springs. Hope they weren't necessary :)

  • peggy331 Sep 09, 2009

    Yes, thanks guys. Need to warn about the plastic rivets attaching the board to the front shell, but nobody should have to do surgery yet on an HP Platinum, anyway. The old HP-12C guys last 25 years!
    Thanks for a pleasingly geeky experience. :)

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2 Answers

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Open it up by removing small screws on the back. Then, gently pry it open. Once you open it, carefully take the rubber pad off the pushbuttons. Then, gently blow things off and wipe it down with denatured alcohol, on a Q tip.

Posted on Sep 09, 2009

  • Craig Butler
    Craig Butler Sep 09, 2009

    There is probably a small screw or two holding it. Any screw going through the board?

  • Craig Butler
    Craig Butler Sep 09, 2009

    There has to be some 'tabs' holding it. Look closely at the edge of the board for tabs the will move back from the edge to release the board. Any screws on the front that could hold it?

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  • Master
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Its not a hard procedure to disassemble the device you should check for the internal touch pad board made up of rubber and plastic,check the touch pad area beside the number 6.if any dust of rust collected clean it.then slightly lift the touch pad of rubber and under that there will be main circuit board.check that also in the place of number 6.if the circuit is short or got dust clean it with isoprophyll and tissue paper.you can get isoprophyll at local medical store.do not apply water to clean the parts. --------- For disassembling----- Tool Description 1)Art knife 803(or any thin strong knife) 2)Screwdriver.(102*150mm).------ Product Disassembly Process 1)Take out 4pcs RUBBER FOOT by hand. 2)Open battery door and take out batteries 3)Use screwdriver to loosen 5pcs screws. 4)To disassemble L/C along unit lower side. 5)Take out 2pcs grounding springs 6)Use art knife to cut off PCB boss. 7)Take out PCB.(PCB means the internal board) ----------- this will help. thanks.please keep updated.please do rate the solution if helped.thank you for using fixya.

Posted on Sep 09, 2009

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1 Answer

How to calculate mortgage pmt using hp. I cannot remember the sequence


There is an excellent computer-based tutorial for the HP 12c Platinum on HP's website (although the sequence for TVM calculations is the same for the original 12c).
Download it and have a look. It will guide you key-by-key through the steps.

calculate-mortgage-pmt-using-hp-cannot-rvrejqbjq4zuw4cbinsyjvsy-3-0.png
http://h20331.www2.hp.com/Hpsub/downloads/cbt_12c_platinum.zip

May 08, 2014 | HP 12c Calculator

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How do you clear RNP for an HP 12C


I take it you mean a 12C Platinum.

Press f ALG. ALG is the f-shifted function of the EEX key, just above the double-size ENTER key. This will switch the 12C Platinum from RPN mode to Algebraic mode, and ALG indicator will light up instead of the RPN indicator.

To switch back to RPN, press f RPN. RPN is the f-shifted function of the CHS key just above the EEX key.

Apr 23, 2014 | HP 12c Calculator

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The following problem is not difficult, however, I am having trouble calculating the answer using my HP 12c Platinum. Can you please provide a step by step explantation of how to calculate the answer to...


1. Make sure the HP-12C is in compounding mode. Press STO-EEX repeatedly until a tiny "C" appears in lower right of display.
2. Make sure "BEGIN" is NOT shown in the display. If it is, press g-END.
3. Clear financial registers: f-FIN. (That is really the "f" key then kind of the "Clear FIN" key -- I'm sure you'll see it.)
4. Enter zero as "initial investment". CLx, then g-CF0. (You have to do this because the 12C actually computes the "NPV" as an excess or deficit over the entered "initial investment". By entering zero, you force the calculator to just give you the actual net present value.)
5. Your first cash flow is +2.00. So, enter 2.00, then press g-CFj.
6. Next cash flow: +2.10. Enter 2.1, then press g-CFj.
7. Last cash flow: +22.20 (the final value of the stock plus the last dividend payment). Enter 22.20, then press g-CFj.
8. Enter the 10% interest (a.k.a. discount) rate. Enter 10, then press "i".
9. Compute the NPV. Press g-NPV. The answer is indeed 20.23 (at least to two decimal places).

Apr 08, 2014 | HP 12C Platinum Basic Calculator

1 Answer

Keystroke sequence


Press 6 . 0 0 5 g square-root

square-root is the g-shifted function of the leftmost key on the second row.

Jul 10, 2013 | HP 12c Calculator

1 Answer

Dim display


If you have the 12C Platinum, turn the calculator on. Press and hold the f key, then press the + key to increase the contrast.

Mar 09, 2013 | Office Equipment & Supplies

1 Answer

Get out of rpn mode on hp 12c


On a 12C Platinum, press f [ALG]

On a non-Platinum you're stuck. It has only the RPN mode.

Jan 15, 2013 | HP 12c Calculator

1 Answer

Stuck in alg mode


Assuming you have a 12C Platinum, press f [RPN] to switch from the algebraic to the RPN mode. [RPN] is the shifted function of the CHS key on the top row of the keyboard.

Jun 21, 2011 | HP 12c Calculator

1 Answer

Alg has shown up on my 12c how do i get it back to orginial format


I presume you're on a Platinum since the non-Platinum 12Cs don't have an algebraic mode.

To switch back to RPN, press f [RPN]. That's the yellow "f" key followed by the "CHS" key.

May 18, 2011 | HP 12c Calculator

1 Answer

I cant find the button to square a value, what does it look like?


There isn't one. You can square a number in two keystrokes by multiplying it by itself (press ENTER then *) or, if stack lift is enabled, by raising it to the second power (press 2 then y^x).

Since it only takes two keystrokes, there was no point in making a shifted key sequence to do it, and keyboard real estate was too limited to devote a key to the function.

Feb 25, 2011 | HP 12c Calculator

1 Answer

My equal sign does not function.


Are we dealing with a 12C Platinum instead of a 12C?

On a 12C Platinum in ALG mode, you don't use the ENTER key at all, but the = key.

Feb 08, 2010 | HP 12c Calculator

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