HP 9825 keyboard restoration

[douze-bis]

The key switches of my HP 9825 are somewhat tired. Sometimes it takes two strokes to input one character, sometimes one keystroke yields multiple characters.
And the overall feeling is not so good.

I have taken the calculator apart to have a better look at the keyboard PCB.
The key switches are all identical and seem to be of the "cherry" kind.

I thought I might replace them with new switches to get a "brand new" keyboard.

Desoldering one key switch was easy enough. However it happens the HP switches are slightly different from the cherry samples I have ordered from wasdkeyboards.com.

The HP switches are taller and their two pins are centered, whereas on the new switches from WASD, the pins are on the side (you may want to have a look at the attached pictures).

At this point I'm kind of stuck.
Does anybody have experience restoring an HP9825 keyboard ?
Which part number are the key switches ?
It is possible order these switches nowadays ?
Are there other keyboards with the same switches ?

As usual, any help will be greatly appreciated

Frederic

[HP67]

If you can't get an answer here, then ask on geekhack and deskauthority. There lies all the world's keyboard knowledge.

[Tom Ward]

Frederic,

Did you have any luck finding a suitable replacement for the switches?
I've a new to me 9825T that is in need of a replacement switch.

Thanks,
Tom

[jebem]

Back in the late 70's we use to repair these keys by cleaning it on Wang Computer equipment at our customer sites.

First immersing them in isopropyl alcohol and shaking them for a minute or so, then let it dry for a few minutes and apply a good quality dry contact cleaner (with no oil) commonly found in electronics shops.

Test it with a ohmeter for zero ohm before reassembling.

[Paul Berger (Canada)]

(02-25-2017 01:14 PM)Tom Ward Wrote:  Frederic,

Did you have any luck finding a suitable replacement for the switches?
I've a new to me 9825T that is in need of a replacement switch.

Thanks,
Tom

I went down that road not to long ago, the keyboard I was repairing had water that had leached through cement drip on the keyboard and it was a huge mess. Water had got inside several key switches, and corroded away internal components others where contaminated with lime so there was no easy solution for them either. I ended up replacing a number of the switches with ones I had salvaged from the keyboard of a 4972A. They fit into the keyboard nicely but the stems are slightly longer and the cross on top is a bit smaller. I used these switches for the numeric keypad and the switches for the top two rows, because while there is only a slight difference in the length of the stem, if they are mixed it would be noticeable. To make the keytops fit on tight I initially used strips of paper as shims, but later switched to narrow strips cut from a pink static bag. These shims hold the key top on tightly with no wobble. I do not know of any exact replacement other than a keyboard from a 9825, 9831, 9835 and lily also a 9845.

If you plan to desolder and reuse a key switch be careful , don't go crazy with heat, but make sure you flow the solder before you pull on the switch or else you may dislodge elements in the switch.

Edit: This applies to the keyboard with the full stroke keys only, the early keyboards used an entirely different switch.

Paul.