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HP Forum Archive 10

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15c "clicking and popping" keys
Message #1 Posted by Joe Edwards on 24 Feb 2003, 12:12 p.m.

I need some advice. I have a 15c that is in pretty good shape, BUT some of the keys when pressed produce a noticeable clicking or popping noise. Is this indicative of keyboard failure? Can it be repaired? Or is it just a mild annoyance. The cals serial number shows a 1983 construction date, so it is 20 years old. Any advice? Thanks.


Re: 15c "clicking and popping" keys
Message #2 Posted by Vieira, Luiz C. (Brazil) on 24 Feb 2003, 1:07 p.m.,
in response to message #1 by Joe Edwards


I have observed this sort of behavior with another associated fact: are the so mentioned keys with a soft-touch feeling as well? If so, chances are you have the probel described below.

I have an old HP15C that has the "clicking and popping" sound plus a soft-touch feeling in about four keys. I also observed the same behavior in a recent Indonesian HP12C. Just an information: all Voyagers, like the HP41, have a rubber sheet (a bit thick) between the keys and the key contacts. Previous models (Classics, Woodstocks, Spices) have a plastic sheet, and some new ones (HP48) have nothing but the keyboard assy itself.

I disassembled the HP12C's keyboard and noticed a few holes under the affected keys, right below the centered pin that actually presses the upper part of the contacts. Well, the keys "stuck" in this hole, causing the "soft-touch" feeling and delaying the contact itself. Noise effects are granted.

Well, that's what happened with my Voyager. I covered the holes with silicon rubber and applied a small, thin plastic sheet over it and rebuilt the keyboard. Not the best solution" (it's not quite good), but I'm gonna cut a new rubber sheet and place it there. I just want to find the best material. I'm collecting suggestions.

I did not open the HP15C's keyboard so far, but I'm getting used to the sound and "soft-touch" feeling.

Best regards and success.

Re: 15c "clicking and popping" keys
Message #3 Posted by Ron Ross on 24 Feb 2003, 1:40 p.m.,
in response to message #2 by Vieira, Luiz C. (Brazil)


How well would a modern 12c work to repair a valuable 15c?

I would hate to see a 15c tossed into the boneyard as long as a 12c could be an organ donar to keep such a valuable calculator alive.

Re: 15c "clicking and popping" keys
Message #4 Posted by Vieira, Luiz C. (Brazil) on 24 Feb 2003, 2:40 p.m.,
in response to message #3 by Ron Ross


depends much on the HP12C's internals.

If it is a Chinese with one button-type battery, I think there are no parts to be "donated", sorry. Even the LCD was mentioned to be not compatible because of the operating voltage. In fact, newer HP12C, Chinese type as decribed above, have a different "font type" in the annunciators, instead they keep GRAD and USER, that are only active when testing the calculator ([ON][+] or [ON][]; this was one of the pilars that made me believe old voyagers would come back). Anyway, for the Indonesian models with three 1.5V button cells and one single IC inside, at least the LCD is compatible, if you donot care for the golden reflexive backplane.

Older models have an equivalent and compatible keyboard scanner together with the LCD module, but it applies only to earlier (first type) models, with two IC's. The keyboard scanner is common to the HP11C, 12C, 15C and 16C (I do not have an HP10C to check for it) and it proven to be fully compatible. I have soem scans I'll upload to a fellow's page and I'll post the address so anyone can download them.

About serial #: I have no information over this subject, but I know many Voyagers' back covers are tradable (I confused myself with three of them and I think I trded them up...) and information may not apply to some "refurbished" calcualtors.

Hope this helps a bit. If you need information about IC's IDs, e-mail me and I'll collect data about it. And post it, if applicable.

Best regards.

...and also...
Message #5 Posted by Vieira, Luiz C. (Brazil) on 24 Feb 2003, 3:02 p.m.,
in response to message #4 by Vieira, Luiz C. (Brazil)

.... if you do not consider only electronics, the rubber sheet is the same in all Voyagers. I cannot figure any key incription that would allow keys to be traded, except for these:

[ON]    [f]    [g]
[0]     [.]    [SIGMA+]
Also, the LCD protective "glass" and battery door (older HP12C)

I think nothing else is tradable.


Thanks for the information
Message #6 Posted by Ron Ross on 24 Feb 2003, 3:19 p.m.,
in response to message #5 by Vieira, Luiz C. (Brazil)

Thanks so much for the speedy reply.

If you allow me to...
Message #7 Posted by Vieira, Luiz C. (Brazil) on 24 Feb 2003, 11:51 p.m.,
in response to message #6 by Ron Ross


I recently brought an HP15C back to life by using an HP11C's guts. I used the 11C's keyboard scanner IC, main/keyboard PCB and case (I had to remove and exchange the keyboard faceplates). The resulting HP15C is a fully working frankencalc!

I have an original HP15C and I keep the newest at home while I take the franken version with me. As the display bezel was a bit bent (a bit "ugly" bent), I took the chance of having it removed and I painted it in metallic gray... Hey, guys, please! It's easily removed with a thinner... I did that just to "mark" it, as I do not intend to sell it, O.K.? This is an HP15C with personality... and still has an ugly, bent, metallic gray, a bit scraped bezel. I'll put my innitials on it soon.

Anyway, Voyagers are not easy to destroy, that's the point. I removed the PQPF IC's and resoldered them with as much care as I had available, and the calculator responded "pronto" to the first battery insertion. I had problems with dirt in the conductive polymers, but after cleanning them carefully, the HP15C was ready to get the road.

Wanna give "your" babe a try?

Let me know.

Best regards.

Luiz C. Vieira - Brazil

Re: 15c "clicking and popping" keys
Message #8 Posted by karl schneider on 25 Feb 2003, 12:25 a.m.,
in response to message #1 by Joe Edwards

Joe --

Can you flex the calculator by pulling in opposite directions at opposite corners? If so, does the noise go away?

If this is the case, you might need to tighten the screws that fasten the case halves. I recently fixed my 1983 unit which had only one "clicking" key by tightening the four screws underneath the rubber feet.

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