How to open a 29C?


Today i bought a 29C in good condition (i thought) however i must press very hard on key 1 and Enter for the keys to respond. I guess a cleaning or something is necessary but how do i open the case???
It's serialnumber is 1710S31422 if that's necessary.
Please respond through mail

Thanks in advance
/Kent (just started to collect)


I´m using a system that does not have an e-mail server installed, so, if you don´t mind...

If I am not wrong, the 29C has the same 25´s case; if so, the two screws (Philips´ fashion) are bellow the two rubber feet at the back cover´s top side, display facing up. After removing the two screws, gently shake the calculator, keyboard facing down. The keyboard assy will pop out a bit; move the assy up and out gently. It will need a bit of ups and outs till it is completely off the back cover.

Now you can do what you have to.


The two rubber feet near the charger connector (i.e., on the back, but at the "display end" of the back) have screws underneath them. Gently pry out the rubber inserts, using a small screwdriver or something. (Be careful, as either the rubber inserts or the back case around the opening may be damaged.)

The two Phillips-head screws should be visible after the feet are removed. Unscrew them, and (as described in the other response), it should be an easy matter to gently separate the front keyboard/display plate from the back case.

Good luck.


Thanks, Mr. Brogger; sometimes, my knowledge of English fails on describing these positional situations. I hope I can count on someones´ help to keep me the right way.

Thanks again.


Thanks to both of you!
I'll give it a try right away!



Be aware that once you follow the instructions of the previous posts, you will still not have direct access to the key contacts. You will have access to a sandwich consisting of the front face of the calculator and a printed circuit board. The key contacts are in the middle of this sandwich. Disassembling this sandwich requires numerous heat stakes to be trimmed and then glued upon reassembly. There have been Forum posts in the past regarding shooting contact cleaner through the little holes that are behind each key, or sticking a fine wire through the hole and scraping it around. I have no firsthand experience with either of these methods.


O.K., this is completely true. But there is a possibility of cleaning the contacts trough the little holes right under each key. Sometimes it´s enough space to CAREFULLY use a small, soft brush or some kind of cleaning device.


My fault... I did not read your post completely, so mine seems just to say exactly the same as yours.



I have fixed way too many Woodstock keys in the past... the best way that I have found is to take three bristles from a small wire brush and chuck them up in a hand held pin vise. Trim the ends of the bristles even. Place a small drop of 91% isopropyl alcohol (or electrical contact cleaner) in the offending key's hole on the back of the keyboard. Insert the wire brush bristles and gently "scritch" around in the hole. Try not to break off a bristle in the hole.

The same technique works for HP41s but the holes are much smaller. Try not to use too much solvent on the '41s because the key click disks are held in place by a sheet of adhesive tape that may come loose. This is why I don't like the technique of spraying contact cleaner directly in the holes.


david; now thats a new one on me. i'll start being very careful how much stuf i shoot in thoes contacts. do you have a guess what solvent may be the least likely to damage the adhesive? water i'm sure, but maybe alcohol? i've usually used more volatile and carcinogenic liquids.


I'm not sure what is the best to use. I have sprayed contact cleaner into 41C keyboard holes in the past and it often times comes out adjacent holes... obviously the tape has come unstuck in places... this can't be good.... but the keyboard still works. Now I always try the wire brush technique first.

My favorite cleaners have been banned by the EPA (ozone remover).

Also be VERY careful cleaning HP25C keyboards with any solvent (including water). For some reason the yellow silkscreen legends on HP25C keyboards (but not HP25 keyboards) seem prone to wash off at the slightest excuse.


"...yellow silkscreen legends on HP25C keyboards (but not HP25 keyboards) seem prone to wash off at the slightest excuse."

Tell me about it...

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