HP 25 malfunctioning keys



#2

Good morning everyone,

I recently bought an HP 25 in very good condition -- excepted that two keys, the [4] and [5], require several presses to get to work. Sometimes I need to press strongly two or three times, sometimes up to ten times before a '4' or a '5' appears. The typical vintage HP "click" feeling is otherwise fine on all keys, including these two ones.

Is there an easy method (maybe similar to the one for the new HP 49g+) to smooth these two keys? Or is is some dust inside?

Thanks a lot.


#3

Hi Emmanuel.

I had this same problem with my 25 (except w/ 4&6), and I over came it by opening the calculator and running a little bit of rubbing alcohol and cloth under the keyboard metal "bubbles". I used a toothpick (as per someone else's post in the museum) with emery cloth to finish.

Works great!

12345


#4

The HP25 keyboards are different than the classics... no key strips to clean under. Most styles of the HP25 keyboard do have a hole in the circuit board under each key. You can clean the keys with a small brush made out of three stands of wire brush bristles chucked in a pin vise, twisted together, and trimmed square. Dip in 91% isopropyl alcohol, place a drop of alcohol in the offending hole, and lightly "scritch" away in the hole.

If your keyboard does not have the holes, you can carefully drill an access hole with a pin drill. Avoid drilling into the circuit traces on the back of the keyboard. Also avoid letting drill shavings into the hole.


#5

It's not a big issue yet, but the number "2" is starting to have similar symptoms on my hp-29c. It sometimes requires several presses now to register a "2".

I'm the original owner of the machine which I've had I think since '77 or '78. (I guess 25 years of faithful service is pretty darned good so I can't really complain..)


#6

Many HP-29C machines have keyboards without the holes. Even worse the circuit board is black and opaque... you cannot see through it to avoid drilling an access hole into a circuit board conductor.

#7

Thank you, it worked perfectly.


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