HP-28S Keyboard



I just obtained a beautiful condition 28s with the leather case. Only problem is that the on key does not register unless you press on the keyboard contact.

I took the overlay off and tried to seat the cover down harder by pressing on the case and melting the stakes nearby. This did not work.

Is the only solution to remove all the stakes and replace the contact foam?


check out the following link:

shucking the clamshell

You have discovered the main flaw of the clamshells. large case and a lot of flexing. in fact there may be many stakes that look good from under the keyboard bezel but are broken at the base. they look whole but are not.

so you will see the repair i did. once painted on the back it looks good and is a lasting repair.

The keyboard stakes most supseptable are the ones by the clasp section. this combined with the depressed foam causes the failure. yes, all the stakes must be milled and then remelted. the broken ones must be replaced. quite a common failure unfortunately.

Get an HP 41CL and get rid of the rest ;-) Of course just kidding. email me if you need more info.


this repair is in the book for this HCC


Sadly, but I advise to remove the battery cover, remove the batteries and then repair the calculator via replacement from e**y. The battery cover and batteries may come in handy with the new clamshell.

Any other repair solution will take lots of time and still have a high probabilty of failure. Just my thoughts.


Got to mildly disagree with the following Ron:

high probabilty of failure

of course, it is dependent on how much time you want to input. This repair was done over two hours with an overnight set on the styrene solvent.

Problem is, this is such a ubiquitous failure (design) at the latch area heat stakes that finding a donor will be problematic. Just ask Randy and his 19BII failure rate.

In any case (pun intended) I have repaired 7 of these in the manner indicated and they are running perfectly! Use the 28S pictured in cockpit to see how durable the new stakes are and the foam replacement is.

Working fine, great machine, poor case design. Now if the hinge was broken then that would be a different story.

Cheers, Geoff

Edited: 26 July 2011, 2:28 p.m.


I'll try the repair at some point in the future.

It's a shame as the unit is unscathed on the outside. Probably just sat there and broke on it's own... Leather case looks really nice too.

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