11C Problems


Anybody have an idea how to fix my beloved 11C? (Actually, my beloved's beloved 11C; I have a 15C.) Here's the scoop:

1. Calculator turns on by pressing any of these keys: ON, f, g, STO, RCL.

2. When f is pushed with calculator on, "f" does not appear in the display. None of the f functions work, i.e., I cannot change from SCI to ENG. "g", however, does appear in the display when g is pressed, and g functions correctly, i.e., I can change RAD to GRAD.

3. No multi-digit number can be entered. If you try to enter 45, first 4.0000 will appear, then 5.0000 will appear.

4. All functions seem to be working, meaning multiplication, addition, subtraction, CHS, exp(x), sin, and so on.

Calculator fails the +, x, / tests with Error 9.

Thanks for any advice!


John --

The 15C manual says simply that, if "Error 9" is obtained for the self-test, the calculator requires service.

However, it also says that if the user wants to continue using the calc, a memory reset (ON/-) should be done.


I´d start by doing a memory reset (ON - Minus).
Then I would try a keyboard test (ON - Divide)

Maybe changing batteries would help also.

Good luck,



The ultimate HP10/11/12/15/16 reset is to short across the outside of the battery string for a second or so with a wire or paper clip while the batteries are in the machine (and YES it says this in the manual).

Another very likely problem is some kind of internal short or (often invisible) contamination on the circuit board. Clean it well with 91%+ isopropyl alcohol. Keep it off the display window or you will get a white stain.

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