Repair of HP32SII



#9

One row of keys does not work on my HP 32SII. Since I cannot replace it I am considering repairing it myself. Does anyone know how to open the case?


#10

Brian:

There are two articles in the Articles Forum that will be worth reading: Article #5 and Article #199.

You may also wish to view the (rather fuzzy) interior pictures available under the MoHPC articles for the HP-42s and -32s (which are other examples of "Pioneer" model calculators).

Contact in the keyboard connections is maintained by a rubbery strip just below the LCD display. Age-related shrinkage of this strip or foreign matter in the contacts are probably the explanation of your trouble. You may experiment with this by gently pinching the calculator front-to-back at various points below the display to see if keyboard function is restored while pressure is being applied.


#11

Thanks Paul I think I'll try it. I pressed on the area below the display and the row of keys began working but fail again as soon as pressure is reduced.


#12

. . . Now to fix it.

I have pulled out the rubber strip and bolstered it (from behind) with a piece of scotch tape, rolled up tightly lenghtwise, sticky side out. That's probably pretty crude, but what you want, I think, is a uniform, approx. 1/16" thick piece of sticky stuff behind the rubber to make it "sit up" better. (Sticky simplifies reassembly.)

Removing and replacing the PCB is THE most tricky part of the operation. Make sure you un-twist the six (IIRC) hold-downs in the proper directions (i.e., you don't want to put a full 180-degree twist in 'em, you want to reduce the twist to zero). Use a small, flat-nosed plier, and be careful not to scratch the PCB.

Clean any dust off of the LCD contacts (gold traces on the PCB, rubbery strip(s) with embedded conductive paths on the LCD itself) before putting it back together. Re-twist the hold-downs and test. (Don't take the rubber LCD strip(s) off of the LCD unless absolutely necessary -- sounds like it shouldn't be in this case.)

Folks who do this a lot have been known to build a "jig" that:

   1. pinches the calculator front and PCB together, 
2. doesn't short any PCB traces, and
3. leaves the keyboard and display free for testing.
(I've yet to build my own, but plan to use one of those yellow plastic ratcheting clamps from Home Depot.) The idea there is to be able to test the keyboard and LCD connections to make sure they're good before twisting the metal hold-downs again. I have pinched them together with my fingers while testing, but ever since my third hand was amputated, that's been kind of rough.

Good luck!

#13

Are all the Pioneers (I have a 32s and 32sii) destined to have this same problem eventually? Is this fix effective in correcting the problem long term? Is the Display going to go bad as a result of time also? What other problems should I expect as these calculator grow old? I'm a little concerned now.


#14

I've seen one other age-related problem with Pioneers: wear in the keyboard "sandwich" leading to missed keypresses.

The keyswitches are constructed as a multilayer sandwich of mylar and other plastics, with conductive "dots" inside plastic domes completing contact when depressed to "fingers" on another layer below. One of my 42s calculators exhibited intermittent failures and had the R/S key stuck "on" occasionally.

Cleaning didn't help much. Disassembly revealed that some of the black conductive stuff had worn and/or flaked off of the dots. Missing material meant missed keyswitches. Loose flakes in some keys completed contact in the absence of keypresses.

I'm in the midst of trying to fix it. (Just got my "conductive ink" pen in the mail.) If the fix-it doesn't work, then the only option is replacement using parts from another, less valuable calculator. (I may also experiment with rotating parts of the "dot" layer 180 degrees, as the wear is asymmetrical. Even translating the dots, say, 1/16" in some direction might help, but that would probably affect the feel of the keys.)

Anyway, I suspect that this may be a problem common to many older and well-used Pioneers.


#15

Does this type of wear occur on the Voyagers too? I have a 15c and I'm hoping the keys continue to work! Thanks.


#16

No, not to worry, the keyboards of all previous model HP's used metal parts in the key switches. The Pioneer series was the first to use the printed conductive materials.

The Classics used metal strips, the Woodstocks, Spices, 41's and Voyagers used either individual or strips of metal domes.


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