HP-29C Key has no 'click'?

[Tom Flatterhand]

I recently purchased a beautiful HP-29C on eBay. It looks like new in almost all aspects. Even the keys all work perfectly. Except for one: it is the '-' (minus) key. It too can be used perfectly without bouncing, but it lacks the smooth 'click' when pressed. My questions about it:

1. does this occasionally happen with Hewlett-Packard calculators?
2. does it indicate heavy use? Because the calculator does not do this in any other way.
3. can I fix this in a simple way?

With kind regards

Thomas Ell

[tangdfx]

Hi，

If you open the Woodstock keyboard, you will find the structure of construction is the same as the classic series.

It could be repaired but not so easy.

[Tom Flatterhand]

(04-02-2022 08:52 AM)tangdfx Wrote:  It could be repaired but not so easy.

Is there a repair documentation for such a operation? A website? A PDF? A video?

[teenix]

There should be notes available for opening the keypad for repair if you do a Forum search.

Here's one that may help.

https://www.hpmuseum.org/forum/thread-17...#pid148751

The keyboard is help together with plastic posts that have had their ends meted to form a mushroom shape at the end. You have to cut the tops of these off and after a repair, the stake tops will have to be glued to the circuit board after reassembly.

If the keyboard has metallic domes, the one under the [-] key may have cracked or has lost its ability to snap back into shape after being pressed and released.

The keyboard might also have the same metallic key strips like the Classics. In this case, the dome under the [-] key may suffer the same problem with fatigue cracking or tensile loss. Sometimes the keys can be pressed really hard and the domes deform and crease also causing loss of tensile strength.

These strips can be repaired but you need a donor.

I documented a repair method in my Classic Notes

cheers

Tony

[Tom Flatterhand]

Hello Tony,

thanks for the tips and the great service manual! You have done a lot of work. I will try to buy a defective HP-25 and open it before I do anything on mine. Because except for the missing click, everything works.

But no one has yet given a hint whether the button has gone defective by excessive use or whether this can also happen once?

I have read a lot about PANAMATIK here and if I get a defective Woodstock model, I plan to install its circuit board. And the GPS! Somewhere there was also a hint that it can be found in Germany in Mainz. That's where my daughter is studying at the moment and it's only 80 km to the Odenwald...

Nice greetings

Thomas

[Maximilian Hohmann]

Hello!

(04-02-2022 01:08 PM)Tom Flatterhand Wrote:  But no one has yet given a hint whether the button has gone defective by excessive use or whether this can also happen once?

That's very hard to tell without doing an "autopsy" of the calculator. I don't know how many calculators of the Woodstock series I have (between 20 and 30 I guess), and among them there is not a single one which has the kind of single-key problem that you describe. Some of them were used a lot (by their looks at least) and still all keys feel the same. One has a keyboard that is totally "stiff", but this is due to heavy corrosion - as if the calculator had been dropped into salt water some time.

Anyway, I can't imagine that from all keys the minus sign sees the most usage. "Zero" or "Enter" must get many more keypresses (probably someone has done a statistics on that) so these should be the first to fail if all were equal at time of manufacture. Maybe someting heavy dropped on the calculator and hit the minus key, or if got squeezed between other items inside a briefcase.

Personally, I would not attempt to repair that key as the calculator is still fully functional. In my experience, once that you take apart the keyboard it will never be as before. You may solve one problem but in change you get two others.

Regards
Max

[AndiGer]

Woodstock's keyboard PCB has a hole on the underside of each key.
Maybe you try to put some contact cleaner into that hole and work it in by pressing the key repeatedly (several minutes)?
Good luck
Andi

[Tom Flatterhand]

Hi Max,

(04-02-2022 01:56 PM)Maximilian Hohmann Wrote:  You may solve one problem but in change you get two others.

thank you for your analysis! I will then do nothing further for the time being. Should I ever get a cheap HP-21 or HP-25, I will explore the repair possibilities.

Nice greetings

Tom

[Tom Flatterhand]

Hi Andi,

(04-02-2022 03:33 PM)AndiGer Wrote:  put some contact cleaner into that hole and work it in by pressing the key repeatedly

Wenn ich den Rechner einmal offen habe, werde ich das ausprobieren.

Nice greetings

Tom