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HP 12c keyboard repair - Printable Version

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HP 12c keyboard repair - Pierre Brial - 06-29-2004

Hi all,

A friend of mine give me an HP12c with a curious malfunction :
The top row of keys of the numeric keypad don't work : this is CHS, 7, 8, 9, and ./. All the other keys work, and the X ON autotest doesn't return an error. Externally, the calculator doesn't seem to have received any damage.
Before to open it I prefer to ask you, friend collectors, if you have any advice about causes and cure of this malfunction.

All the best

Pierre Brial
Reunion Island

Re: HP 12c keyboard repair - Renato (Brasil) - 06-29-2004

I had one HP-12c (Made in Malaysia) with this problem. This row of keys, in this one-chip unit, is connected to one CPU pin. This CPU pin had a bad solder. Fixing was just a matter of carefully heating this pin.


Re: HP 12c keyboard repair - Randy - 06-29-2004

What's the serial number?

Re: HP 12c keyboard repair - james summers - 06-29-2004

Hi Pierre

The symptoms sound very familiar as I had a similar problem due to one pin on the CPU not being soldered to the board. I can do no better than refer you to this thread:
where I found some very good advice which enabled me to fix my 12C which is still going strong.

As Luiz would say....


(and let us know how you get on)

Re: HP 12c keyboard repair - james summers - 06-29-2004

Hey - how about that - co-ordinated posting!!! A new Olympic sport?

co-ordinated posting!!! A new Olympic sport? - Renato (Brasil) - 06-29-2004

My first win ! Yeah. I must say your research has dragged you. Interesting : I posted a very similar comment one year ago, and did not remember it !


Thanks mentioning d8^) (N.T.) - Vieira, Luiz C. (Brazil) - 06-29-2004

123456 to remove

HP 12c **REPAIRED** - Pierre Brial - 06-30-2004

Hi all,

I've been deeply impressed to receive, within 50 minutes, four wise answers to my post.

Thank to you, this HP12c is now repaired. One other saved !

It is indeed a Malaysian unit, serial Number 3635M01102. The faulty pin was the one pointed out by Randy Sloyer : second from the bottom of the right row. It was not possible only visually to see that this pin was not perfectly soldered on the board. Even with a multimeter I had some doubt, because when you test the pin, you press it, enabling the contact !
The contact was soldered again by pressing the pin with a small screwdriver and making melt the solder with the iron.

I was surprised not to find in the calculator the famous voyager's polycarbonate wrapping.

Thanks again

Pierre Brial

Congratulations, excellent news!! (N/T) - james summers - 06-30-2004