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hp 12c (platinum) - Performing Keyboard Self Test

This is a simple test to check that all the keys are working properly on your 12c or 12c Platinum.

To perform the keyboard / display test, with the calculator off, press and hold the divide key, press and release the ON / OFF key, then release the divide key.

Press each key in order from left to right on each row, from the top row to the bottom row. As you press the keyboard, for the first (top) row 4 segments will be displayed at any one time - so this gives you a chance to check the display (or dead pixel). And on the second to fourth rows, you see only 2 segments. You need to press through the Enter key twice, once when testing the 3 row, and second time when testing the 4 row.

At the end of the test, it should show 12.

If your key sequence is wrong, you will get "Error 9". Press Enter and repeat the test.

Updated On: 12.09.20


  1. On 28-Nov-2015, Janna wrote: 
    My hp12cplatinum is displaying error 7 when trying to calculate the irr, I've read above and have done the self test fine but the key test isn't working out as it should. Any other suggestions? I just need the irr fixed, please!
    Your reply to Janna

  2. On 05-Oct-2015, Ron wrote: 
    It sounds like your % key was mashed (pressed to hard) in by either a book in a back pack type event or crushed to where the keypad dome under the key is flat. While this can be repaired, it usually involves taking the calculator apart and re-popping the dome. Hp does not repair these types of failures, but if your calculator is under warranty, they will replace.
    .
    If it is not under warranty, you can certainly attempt repair. However, be aware that you will likely ruin you calculator if you are NOT experienced with electronics. If the calculator is functional, I would suggest you buy another (used even) and keep this one as a back up. Yes, the Hp 12c can be repaired by others (look up repair for the Hp 11c or Hp 15c). However, the cost to repair will exceed the value of your Hp 12c calculator, the other Hp calculators listed are no longer available and MUST be repaired as they cannot be replaced.
    Your reply to Ron

  3. On 01-Oct-2015, Celia wrote: 
    The % key on my HP 12c financial calculator is unresponsive. It is difficult to press and does not calculate. Blowing air to it does not work, What do I do? I really need it to work because of the business I am in. Thanks
    Your reply to Celia
    • On 27-Jan-2018, Marcel replied: 
      The enter key on my favorite HP 12c Platinum would only work by pressing hard and I fixed it by doing the following:
      1. Remove the 5 screws in the back and open up the calculator without losing the two tiny springs in the back plate.
      2. Using a sharp knife, cut the plastic holding the board to the keyboard. There are several thin layers of plastic to cut before the board will come off.
      3. Put a piece of masking tape rolled up on the key that is not having proper contact with the board.
      4. Put the board back and hold the battery in place to test the key. The tape should be against the key and rubber mat.
      5. Put the calculator back together.
      Your reply to Marcel

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