HP-25 Keyboard fix, dissambely advice ?

[allstonma]

Hi All
I have inhereted my fathers old HP-25 and the battery pack seems to have leaked and effected the keyboard. Got the case apart, but need to remove the board with the buttons from the front cover. Any advice on how to do this ? Does not seem to be an obvious method.
While were at it, seems like the battery door is stuck, and advice on this as well ?
Many Thanks
Allstonma

[BobVA]

The keyboard is heat-staked together and is not designed to be disassembled, unfortunately.

If it's just a few keys not working, though, this post may be of some help.

[Benoit Maag]

Allstonma,

It is not easy but the keyboard should be fixable - I fixed a completely corroded keyboard a few months ago

The first step is to cut off all the little black bubbles (post tops that stick out of the keyboard back) with a razor blade
That allows you to disassemble the keyboard. You can then clean up the keyboard corrosion with vinegar (for example). You probably need to scrape off corrosion from under the ‘cricket mechanism’ (bent metal tabs that click to register the keys) - I used a thin enameled wire for that

After the cleanup, you should check that the keys register using an ohm meter
You also may want to cleanup the off/on and prgm/run sliders as well and add silicon grease to smoothen the sliding mechanism

To seal the keyboard back, make sure you clamp the front and back parts tight and drop ABS glue with a syringe on top of each post to replace the original black bubbles you cut off (I used successfully Oates medium black abs cement which I bought at a hardware store)

If the rest of the machine is completely corroded and does not work, you can get a Woodstock LP kit from Panamatik which will give it a new life

Good Luck!

[olcuretti]

(08-12-2018 06:02 PM)allstonma Wrote:  Hi All
I have inhereted my fathers old HP-25 and the battery pack seems to have leaked and effected the keyboard. Got the case apart, but need to remove the board with the buttons from the front cover. Any advice on how to do this ? Does not seem to be an obvious method.
While were at it, seems like the battery door is stuck, and advice on this as well ?
Many Thanks
Allstonma

Hi!, I just fixed a similar problem, the battery leak was so bad that several buttons were not working and the number 4 was not even toggling, completely stuck, no need to split the keyboard, just using a small metal blade (TIC transistor contact) bend 2 mm at its end and spin it through the back golden hole while toggling the button get it released and dirtyness loosen, further blowing with air compressor and works fine. In fact, the circuitry needed some cleanins as well and one contact leg had to be rebuilt as it was missed, some piece of desoldering mesh was welded to the circuitry run (which was reinforced with a welded wire) then some rigid glue in order to make the contact strong enough.
The cover holes were enlarged a bit to allow easy reassy.

[Geoff Quickfall]

Before disassembly, and a rather drastic disassembly look at this post.

PCA pores

The Woodstock’s also have pores from the PCA into the contact domes. At least in the 50 or so I have looked at except for one!

If you are lucky, and have the pores then introduce some de-oxit red into the pores and swizzle it around with fine wire. Not to much de-0oxit red is required. If no de-oxit on hand then just use the stiff fine wire and swizzle it around.,

Don’t use solvents or even IPA as it may exit the front and affect the silkscreened overlay.

If this doesn’t work then disassembly (but avoid that at all costs).

[GreyUser]

Pores? On a printed circuit board, they’re known as a via. Plural is vias.

Removing the printed circuit board from the plastic plate is a very bad idea indeed and it gets you no closer to the problem which is easily solved from the back side of the printed circuit board.

Avoid disassembly of the heat stakes at all costs. The keyboard will never be the same even should you reassemble it somehow.

[Geoff Quickfall]

As GreyUser accurately points out, the ‘pores’ are vias. I just didn’t want to assume everyone here including me is an electronics engineer ;-)

Just as the card reader does not have a clutch but rather a ‘dampening couple’ used to prevent vibration from the motor transferring to the card as it is read.

Cheers, Geoff