HP-15C Sticky Keys


I tried the alcohol drop with homemade brush technique to clean up about 7-8 stick keys. Technique While the alcohol was liquid, the keys didn't stick. When it evaporated, they started again.

I do not have access to an ultrasonic cleaner. Would anyone suggest soaking the calculator in heated (not boiling) deionized water below the LCD? I could then heat/dry with a hair drier.

Other suggestions?

Hmm, maybe my dentist would let me borrow his water pick :)


I have no idea to solve your problem except maybe opening the HP-15C and cleaning the key contacts.

But I would like to know if the idea to use an ultrasonic cleaner would be appropriate to clean the keyboard of a woodstock calculator? Of course, only the keyboard not the entire machine.
I would open my woodstock which has some keys which needs to be pressed very strong to be recognized and put only the keyboard into the ultrasonic cleaner.
Would this work? Is there no danger in damaging the keyboard?




Do NOT use a ultrasonic cleaner on a Woodstock keyboard as this will fragilize/erase the keyboard markings.

A procedure that works (I use isopropyl alcohol) can be found


Edited: 6 Feb 2011, 9:49 a.m.



To disassemble a Voyager: I use the excellent procedure from Luiz: here.

To clean the keyboard: I use Randy's steps: here.



Thanks Etienne,

I guess I will "dive in" to the distilled water solution. I don't know what foreign substance is causing the stick. (I just purchased the unit). Hopefully it is water soluble.


The disassembly procedure in the thread referenced just above applies to the early models of the Voyagers in which the logic and LCD assemblies may be separated from the keyboard assembly.

The later models (after 1984???) utilize a much less complex configuration in which the logic and display and keyboard are all constructed on one large PCB.

This difference makes some display or keyboard repairs that are possible on one version impossible or very challenging on the other.

Most descriptions of Voyager disassembly assume that the early internal configuration is what will be found. Even this site's museum shows, AFAIK, no photos of what is likely the more common later internal configuration.

Randy's (of Fix That Calc) recommendations would carry the most authority and promise for success.

Edited: 6 Feb 2011, 11:50 a.m.


I've done the distilled water cleaning and alcohol dropped into problem keys. No success. Is the cause of sticky keys ALWAYS caused by some foreign substance or do they start to get this way with age?

I'll do it again if consensus is substance as they are somewhat annoying (but work fine)



For openning your calculator, you must cut off all the plastic seals on the main print circuit board. Use a good knife for this and let the plastic pins behing them intacts.
So, remove the rubber sheet and proceed with a good cleaning, using alchool.
To put back the pcb, you will need to make a support with many plastic plastic pins that goes bethween keys and use some fast Epoxi (10min cure) and some very heavy pieces to keep all togheter.
It's is not so difficult and I have done this for a number of calculators, including 41C? models.


Perhaps I am not describing the issue well.

It seems that the keypad membrane snaps or clicks after depressing. the feel correct, but there is snap just as the key returns. There is no sticking of contact (as in multiple digits)

Would this still be foreign matter?

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