hp 22s - '7' key problem


I recently managed to get a hold of an hp 22s after trying for the last few months. The '7' key seems to have a problem. It works when I press on the right side of the key, but not on the left side. When pressing on the centre,more or less every alternating keystroke registers a '7' on the display. I discovered this problem when I tried to do SHIFT + LIBRARY because the EQUATION LIBRARY didn't seem to come up. I have tried blowing compressed air as suggested somewhere in the HP Forum archives, but this doesn't help. I mean it isn't really a problem since I am now aware of it, but what I would like to know does this mean this key is about to give up the ghost?


The 22s is a "Pioneer" style calculator. There seem to be three approaches to problems like this:

It has been suggested elsewhere (by Randy Sloyer) that three twenty-minute baths in distilled water in an ultrasonic cleaner, separated by long drying-out periods (perhaps near a heater, or on top of a refrigerator) should clean out a Pioneer keyboard with foreign goo inside.

Sometimes the keyboard-to-circuit-board contacts aren't tight, but if that were the problem, I'd expect several other keys to behave similarly. To double-check this, pinch the calculator front-to-back (firmly, but gently, as the hackneyed phrase goes) just above the top row of keys, and below the display. Deep inside there is where the keyboard contacts the printed circuit board. If the contacts are loose, the pinching should (temporarily) improve that and therefore improve the behavior. If this diagnostic trick indicates bad contacts, you'll want to take the calculator apart, take out the circuit board, clean both sides of the keyboard-to-circuit connections, and bolster the rubber/latex/whatever pressure pad that maintains contact. (One theory is that the rubber gradually shrinks with age.)

Finally, I have fixed keyboards in prized units by taking apart the several layers and replacing them with less-worn equivalents from a less-valued calculator. But this requires an extra "parts" calculator that hasn't yet been worked to death. The procedure is invasive, tedious, and fraught with potential for complications, so only undertake such a repair as a LAST resort. (I.e., live with an imperfect key, if that's an option.)

Good luck -- and post again if you need more help.

-- paul b.


If the key rocks from side to side, one or both of the small internal hinges that stabilize the key could be broken.

Try pressing on the left side of the key, then the right. If both sides move when one side is pressed, the hinge is okay. If not, one or both sides are broken.

It takes a direct, centered downward force to make proper contact between the upper flex dome and the lower cross point contact. There is a small, flat ended actuator pin centered on the upper part of the key (it's right under the top horizontal line segment of the 7) that deforms the dome when pressed. If the key's hinge is broken, the flat end of the pin no longer hits squarely, resulting in missed key presses since the contact area is significantly reduced.

Eventually, after lots of key presses where the sharp edge of the pin is pressed at an angle on the flex dome, it will cut through the mylar dome sheet. The result is a dead keyboard. Replacement is an ugly thing at best, as it takes an organ donor and lots and lots of time and patience.

A photo of the hinge on the enter key of a 42S, you can see the actuation pins.


Gents, Thanks for your replies. I checked as you suggested Randy, but the hinge seems to be OK ie. the key presses down level when I push either on the left side or right side. So perhaps it is some goo that has gone down the left side of the key.

I was really only concerned if this symptom was a sign that the key was about to break fairly soon. If it is just some goo stuck under the left side of the key then I'll live with it since that is the only key affected on the calculator, and at least it is still functional.

By the way Paul, when you talk about keeping a cheaper pioneer or two for parts in case a more prized one breaks, does this apply with keeping say a 10b in order to fix a 27s or 42s, or does it need to be something like a 17bII?


The keyboard is common to all Pioneer series machines. One size fits all, but there are non-electrical differences with at least three different versions. If you swap all the pieces out as a group, they can be considered interchangeable. The metal keyboard backing plate that also holds the LCD is part of that group.

The LCD matrix is:

10B = 20S
17B = 17Bii = 27S = 42S
14B = 22S = 32S
The 32Sii is unique


Randy's response is more complete than the one I might have offered, and is absolutely correct in all particulars of which I am aware. Randy, you're a great resource for the folks utilizing this site. Thanks!

The first Pioneers that I experimented with were several service-replacement 14B close-outs bought from EduCalc for $20 each. Those days are gone. But don't be afraid to buy "broken" units, when available. (Example: the last 42s I bought was listed as a "Parts Calculator Only", but simply has a sticky keyboard and some minor cosmetic damage from a clumsy take-apart job -- I've already upgraded its memory and moved the PCB to a working case, pending a keyboard fix . . . )


Have you considered just exchanging the ROM from a 42s onto a 17b. Wouldn't that be a lot less trouble than messing with a keyboard? I do realize you would not have a 42s keyboard layout, but you would get brand new keys and newer everything as new 17b's are fairly easy and cheap to find.

Just curious as to the feasability?


I've changed circuit boards. In fact, because I'm always wringing maximum $ out of every genuine 42s I can get working, my "personal" hot rod is a shiny new HP-17BII with a 32K HP-42S circuit board. I've painted the keys and keyboard black, except for those which are neutral or agree (STO, RCL, UP, DOWN, SHIFT, the numerals, the arithmetic operators, etc.)

I used to think I could memorize the layout, but I don't actually use it often enough for that. So, I've got a ~full-scale color print of the original MoHPC -42s keyboard image -- cropped, laminated, and attached to the back by a clear tape "hinge". I fold it out to use anything beyond the basics, and fold it back when storing the calculator in its case.

Despite my contrary report in an early repairs article (I should update that!), the ROM is actually part of the processor chip. There is a second chip, but it's RAM. (That's why we can upgrade the -42s from 8K to 32K.)

If I remember correctly, Tony Duell somehow discovered that by tying an "off-board ROM enable" line low (or whatever), he could cause the CPU to consult an external ROM (I think located in the extra set of pads on the PCB). So, if one had the right PROM programmer, intimate knowledge of 42s internals and Saturn Assembly Language, one might be able to hack the 42s operating code! (Potentially VERY cool, and about as esoterically geeky as one might get!) On a simpler note, one might convert -17BII PCBs to -42S functionality if one could produce the right PROM (without angering any copyright holders . . . )

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