HP 9825 keyboard restoration

douze-bis

05 May 2014, 22:28

Hello !
I’m trying to restore an "antique" HP keyboard.

The keyboard belongs to a desktop calculator from the 70s (HP 9825A). It is a little "tired" : sometimes two keystrokes are necessary to input one character, sometimes a single keystroke yields multiple characters, and the overall typing experience is not too good...

My intention is to de-solder the key switches from the keyboard PCB and replace them with new switches.

I have taken the calculator apart to have a better look at the keyboard PCB.
The key switches seem to be from cherry corp. Unfortunately, they are not identical to the switches that can be ordered from (say) WASD.
They are taller, and the two pins are located differently.

For clarity, I have uploaded a few of pictures on my flickr account.
https://www.flickr.com/photos/78824170@ ... 101724017/
Pictures 1 and 2 are of the HP 9825 key switch.
Pictures 3 and 4 are of a cherry switch (Cherry MX Brown Keyswitch - MX1A-G1NN).

So... I have a few questions:
- Would anybody know the part number for the HP 9825A key switches ?
- Is there a way to supply these switches nowadays ?
- If not, do other keyboards use the same switches ?
- Or maybe there’s a better/simpler way altogether to restore antique key switches ?

Any help will be greatly appreciated,
Frederic
Attachments
HP 9825A keyboard
HP 9825A keyboard
20140505_222035.jpg (110.28 KiB) Viewed 998 times

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Daniel Beardsmore

05 May 2014, 22:53

Interesting — the legs on the "HP" switch are positioned front and back.

Some more photos of the unknown switch would be nice.

Here's one we've never identified, that's quite close:

https://plus.google.com/photos/11384566 ... 4565789137

Disassembly shots here: http://sandy55.fc2web.com/keyboard/y1700.html

Cortron suggested to me that Fluke made that switch, while it closely resembles an ITW patent. My guess is that it's some Licon/ITW/Cortron variant, as they made a whole load of interesting switches back in the day.

Edit: Actually I'm pretty sure that's the same switch family as yours — all the little details match. In which case, no, we don't know what it is yet :)

douze-bis

05 May 2014, 23:43

Thank you Daniel !

Yes, the HP switch looks remarkably similar to the unidentified Fluke's one...
We're making good progress :)

I have added a few pictures to the flickr album.
Including a picture of the back of the PCB.
The pictures are a little blurry and it's not easy to see, but the "HP" switch has a "24" marking on one side and a "23" marking on the bottom, next to its broken leg.

Frederic

PS : And I believe the legs on the "HP" switch are actually positioned centered left and right, not front and back.

douze-bis

05 May 2014, 23:49

By the way... I noticed that both the "HP" PCB and the "Fluke" PCB have 4 soldering "holes" per key.
Considering that keyswitches only have two legs, that would be 2 holes too many... ?

Do you know the reason for the 4 holes ?
(maybe the capability to fit different kinds of switches ?)

User avatar
Daniel Beardsmore

06 May 2014, 01:17

Well, with a cruciform slider, you frequently have 90° rotational symmetry. However, what's interesting here is that, when you look at the plane of the legs, they're positioned front to back, as shown on the right here:
Leg positions.png
Leg positions.png (5.9 KiB) Viewed 973 times
Most switches are arranged as shown on the left.

That's what gave me a clue where to begin.

Indeed, the switch is not quite the same. You should take one apart and see what's inside; you may find that the contacts are dirty, or that they need bending a bit.

You may find some spare switches from someone else with a busted calculator, but I doubt anyone here is going to know what those switches are (if anyone does, they'll been holding out on me all this time! ;-)

The extra holes in the Fluke PCB may be to permit more than one switch to be used, for example.

Edit: Doh, I thought we were being shown the Cherry MX switch because some keys used it, not because the OP felt that he needed to teach us what a Cherry switch looked like …
Last edited by Daniel Beardsmore on 06 May 2014, 09:21, edited 1 time in total.

Findecanor

06 May 2014, 02:28

I have had a HP keyboard with identical-looking keycaps, but it had Cherry M11 switches. It looks to me as if the Cherry M11 might be compatible to these switches, at least in pins and keycap mount.

I gave the keycaps to Ascaii. I think he used them with some vintage Alps or Cherry M5.
I trashed the rest of the keyboard ... because many switches were broken and the remaining were brittle and had awful key feel, so I don't have any left.

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