I have an HP 11C that has the third digit after the decimal that is partly missing. I bought and installed a display from a 12C as someone told me this would work. It did not. After running the diagnostics, the display should read 11, but read 12. Also, some functions such as roots and squares do not work correctly.

I need some help.....thanks!


Hi, Fred;

can you describe what part of the display you actually replaced? For me, it's enough to see the

 [    12    ]
after testing the keyboard to tell you that this is an HP12C, not an HP11C. That would also explain the "awkward" operation. Please, have a look at the image below:

If this is what you replaced, you actually brought an entire HP12C to the inside of an HP11C (this image shows the inside of an HP15C, in fact, but they all look alike). In fact, the LCD itself cannot hold information related to the calculator operation. One single test you can perform is keying in a number and after the third digit ahead you press the back-arrow key [<-] and see if the rightmost digit is cleared. If the entire display returns to [0.00] than you are operating an HP12C. Also, after a memory clear procedure ([ON]&[-]) you should see four decimal places if it is an HP11C. The HP12C's default is two decimal places (financial default).

Let us know if you need more advice.

Luiz (Brazil)

Edited: 2 Jan 2005, 4:59 p.m.


Thanks LUIZ,

I replaced the whole thing. The whole picture of what you sent in your email.
The display, battery contacts and the like.

I used one from a 12C, because somebody told me it would work. It doesn't.

I need to buy one from an old 11C.

Thank you for your reply.

Happy New Years to you and your family,

Fred Rumak
Calgary, Alberta, Canada


Hi, Fred;

I'm glad you could identify it.

The fact is that it is possible to X-change the LCD assembly, but I had no good experience when dealing with this type of construction. There is no need for soldering, but electronics and "mechanical" expertise is required, because there is a metal frame (that you have probably seen in the front side of the display assy) that needs to be carefully bent to release the LCD and both polymers. The structural shape of this frame must not be changed, because it must be used to keep everything back in place.

You may find some serious, pro technician that is able to exchange the LCD assy only. If not, try fixthatcalc and they'll surely put things back togheter.

Best regards.

Luiz (Brazil)


Hi to all of you!
Vieira is correct about taking care in exchanging the display only. I've already done this in one HP15C and it was tedious to put all the display's digits to work properly back again.
Remove the metal frames, remove the displays (take care do not remove the spaget rubber back it) and exchange them.
Replace the frame and tight it well. With a small screw driver, adjust the spaget over the PCB contacts until you get the display working correctly.
By these days, I'll make this procedure again with another 15C and the display of one old 12C.

Best regards - Artur - Brazil!

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