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HP Forum Archive 10

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Re: HP 15C - broken key?
Message #1 Posted by Bob Fourney on 21 Jan 2003, 12:08 p.m.

I also let mine sit for awhile (maybe a year). Upon replacing the batteries, everything works EXCEPT the division key (upper right hand corner key). I've been using it for mundane household stuff since then, so the 1/x key has served me well. Now I might need to use it as a real calculator again, and might need the other functionality on that key. I have two questions:

1) This seems like it'd be easy to fix, if I knew what I was doing. I started to take it apart, and then chickened out (this was a year or so ago, I forget if I really got nervous or just realized that the 1/x key would do all I really needed to do). Is this something I can take apart, clean or bend something and put back together? Or is it more complicated?

2) I like the size of the 15C, I don't need graphics or a lot of programability. I also like RPN. Does anybody sell a modern equivalent? HP sure doesn't seem to.

Any other ideas?

Bob Fourney

Re: HP 15C - broken key?
Message #2 Posted by David Smith on 22 Jan 2003, 6:09 p.m.,
in response to message #1 by Bob Fourney

Most of the HP calculator keyboards have a small hole under each key contact.

If a key has problems making contact or causing double entries, etc. you can almost always fix the problem by making a tiny wire brush out of three bristles from a larger wire brush (I use one of those cone shaped brushes made to be chucked in an electric drill).

Mount the bristles in a razor knife holder or pin chuck.

Twist the bristles together.

Trim the end square with wire cutters.

Place a drop of alcohol (91% isopropyl) in the offending key's hole on the keyboard printed circuit. Be careful not to get alcohol on the display window or keyboard front... it can stain. Dip your tiny wire brush in more alcohol.

Gently scratch around in the offending keyboard hole with the brush. Be careful not to break a bristle off in the hole.

I have seen some woodstock machines with the holes under each key. I fixed one by carefully drilling a hole under the bad key, carefully avoiding the circuit etches on the other side of the keyboard.

Re: HP 15C - broken key?
Message #3 Posted by Vieira, Luiz C. (Brazil) on 22 Jan 2003, 9:59 p.m.,
in response to message #2 by David Smith


voyagers are exactly like this: the holes are right under the center of the keys' contacts.

I cleaned the contacts for [2] and [3] keys of my HP15C in this very last weekend and I used the same procedure you mention. It is a lot efficient.

BTW, Bob, let me ask you a silly question (based on the facts you mentioned in your post): do you know how to open the calculator? If you have not done it before, there are four screws under each of the four rubber feet. And please notice that there are two small springs connecting the two upper bezels and the back label, vertically positioned. If you believe you will turn the calculator up while the back half of the case is removed, remove and keep the small springs in a safe place. One of them is right beside the batteries compartment and the other is in the middle of the keyboard, extreme right.

Success, Bob.

Re: HP 15C - broken key?
Message #4 Posted by Bob Fourney on 23 Jan 2003, 3:27 p.m.,
in response to message #3 by Vieira, Luiz C. (Brazil)

Thanks for the responses.

I have had the back off of it before, I don't remember the tiny springs, but must have gotten them back in since it still works (as well as it did before I opened it up).

I was reading a post here the other day, which sounded like I need to fabricate some shims to and crazy glue the pcb back onto the front of the calc when I'm done. That sounded like more than I want to attempt right now.

I'm teaching a class this semester that'll require the use of the trig functions and some basic vector stuff, so I can muddle by without the "divide", "solve" and x><y" functions (the functionality on the single broken key), but I don't want to break it and have to learn algebraic entry at my advanced age. I'll probably pop the back off one more time and see how far I can get without breaking something. A co-worker showed me her 32S ii today, and said "buy one of these instead", but I see that they are also no longer made. Arghhh. I'm not a marketting guy, but I'd think if you have people willing to pay $100 for a basic RPN calculator instead of $11 for an algebraic entry casio, you'd offer the RPN calculator?

Thanks again for the responses,

Bob Fourney

Re: HP 15C - broken key?
Message #5 Posted by David Smith on 23 Jan 2003, 7:19 p.m.,
in response to message #4 by Bob Fourney

If your problem is just a dirty key contact there is no need for any calculator surgery beyond removing the back of the machine.

Re: HP 15C - broken key? - an add to David's precise answer
Message #6 Posted by Vieira, Luiz C. (Brazil) on 23 Jan 2003, 8:43 p.m.,
in response to message #4 by Bob Fourney


David is completely right: there is no need to remove the keyboard and reinstall it back.

I'l send you an image of the back of an openned calculator and I'll point out where to clean. So, please, read the very good explanation written by David Smith in his previous post in this same thread and check the image I'm sending you in a few minutes, right? Then you try the actual calculator.

I hope you have success.

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