HP-15c Powering on

Hi all,
just bought a 15c that seems okay, just the on button does require a little tough pressure to activate.
The calculator has not been used in several years, self tests are okay.

Do you have any suggestion to fix it? will a little exercise take care of the problem?


Giuseppe Marullo

PS: I am in dire need of the advanced functions pdf, so if any good soul...


I cannot advise wrt the sticky 'ON' button, for that you need Randy or Geoff Q. But I can tell you that the Advanced Functions manual is available for purchase on CD or DVD from this very site. Good luck! -- JeffK


I am in dire need of the advanced functions pdf, so if any good soul...



Many thanks for your information, but acquiring DVD will cause me to buy more HP calcs, I already have way more stuff I can reasonably use...anyway I "solved" thanks.

Still have to understand how to deal with the sticky on button...

Giuseppe Marullo


Hello Giuseppe!

I am sorry I did not get in touch earlier but I was away in London, England when you posted.

Try this link posted awhile ago at the hpmuseum:

After reading that try this step first. Take an eyedropper with 99% alcohol and place a drop on the ON key (or any sticky key). Exercise the key by repeated pressing. Let the alcohol dry by using forced air or passively by letting dry over time. This should cleanup any oil residue.

sticky key 15C

If this did not work, take an eyedropper of water and place the drop on the ON key (or any sticky key). Again exercise the key and then allow to dry. Use a dropper of alcohol after the water to expedite the drying process. This will clean up the sugar residues.

Let us know how it works out.



Hi Geoff,
sorry to bother you with this, I already saw your article, just wondering if this is a case of dirt or something else, I will try the alchool eyedropper trick and report any progress here.

Do I have to remove batteries?
Suppose I don't have a dyer box, how many days should I allow it to dry?

The key always registers, is the huge pressure I need to perform to make it happen tha puzzles me.



The water and alcohol should remove grime that seeps under the key domes. Dirt, grit and etc that is physically stuck will require the wash technique as described in the linked posting.

Try the water and alcohol dropper solution with the batteries out. Shake the water and alcohol out after exercising the key. If you have a hair dryer warm the area around the key. Not to hot but bursts of heat. The idea is not to heat up the calculator but to accelerate the drying.

If you just air dry but are thorough about shaking the water out then a couple of hours should be fine. In fact, if the water drops are confined to the key itself then the shaking or blowing and blotting of the key should suffice for a quick test with the batteries in within minutes of doing the cleaning. Confirm it works then let dry overnight.

If you end up soaking and washing the keyboard under water then the drying period would be a couple of days without a drying box.

Second point about pressure on the key.

Open the back of the calculator. Looking at the calculator inside front at the Circuit Board (CB). Find the area associated with the ON key. Press the key and observe the plastic rivets surrounding the ON key area on the CB. Are these rivets secure or is the CB flexing outward, that is, do the rivets hold the CB in place? If not then it is the rivets which are allowing to much travel for the ON key prior to it contacting the CB. Try pushing on the area of the CB near or at the ON key and simutaneously press the ON key ON, batteries in place. See if this helps in contact. If the rivets flex and the pressing action on the inside of the calculator works then read on.

To fix this, you will have to press down on the Circuit Board and melt the heads of the loose rivets with a flat soldering iron element or hot knife. Heat just enough to soften the rivets, not melt them. Do this while applying pressure.

Another way to enhance the contact between key and board is to place a thin foam cushion in the vicinity of the offending key and the screw the back of the case in place. This to will add pressure and help hold the CB against the keyboard contacts.

Cheers, Geoff

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