An idea for repairing Spice series machines with keyboard problems


I have an idea on how to solve the issue of erratic behavior and keys not working on the Spice series calcuators. To me it seems the problem with these older solderless models is that the foam between the keyboard PCB and the metal plate is getting old and flattening out, not making good contact between the 2 layers. It might be possible to get rid of this sticky foam, using some kind of adhesive remover, and replace it with a sheet of rubber, maybe adhesive stuff like the bottom foot on the new HP-35s. This wouldn't flatten out as badly as the foam would, and if it was the correct thickness, should give the pressure needed to make good contact.

I'll try this out on my spotty 33E and let people know how it works out.


... and had some good results.

Hi, Lincoln;

because of both the HP38C and the HP34C, I devoted some time trying to maintain Spices the best way possible. I have some solderless and other soldered units, and all of the solderless have bad contact in the LED display from time to time.

I once reasoned about the three following procedures which significantly reduced bad contact behavior in the IC´s. In fact, I never saw 'Pr Error' anymore since then.

- polish the contacts of the flex circuit - I use metal polisher and a cotton swab;

- apply a thin coat of any micro oil over the contacts - I use a very thin coat of WD40 spread with a clean cotton swab; it does not avoid the IC´s terminals to touch the surface of the flex circuit and also protects the remaining surface of the tracks against oxidation (not highly efficient, just a reasonable protection)

- slightly bent the tip of the IC´s terminals; look at the drawing below.

With these three basic procedures you may achieve so many good results you´ll probably not need to replace the foam. My four solderless Spices work pretty fine, but sometimes one segment or a whole digit misses. I simply tap it gently in my hand sideways and up/downways and it gets back to normal. The LED display contacts are in the edge and I also slightly bent them, one in the opposed direction of the other (as experts do with saw teeth).

Hope this helps.


Luiz (Brazil)


The foam is one aspect of the problem, a bigger one is the oxidation of the IC leads from battery outgassing.

So I clean the leads of the IC's and LED array then solder the thing together. End of all problems.

Until the keyboard starts to fail... which it will with continued use.


Ah, OK. Yeah, this entire thing got blasted with Deoxit when I got it, which probably took care of the IC lead corrosion, as well as fixing the problem with some of the LEDs being dim.


Hello Lincoln,

Sometimes the oxidation actually affects the metal contacts. That is, it is not always a residue that prevents contact but also a surface oxidation of the metal on the contact.

This may require a mechanical removal. Using a fiber glass pen has always worked. It is a mild abrasive, that is very controlable, vis-a-vis how much surface you would like to remove. A clean with denatured alcohol and brush and away you go.

I have restored 6 spice versions this way, all solderless and with depressed foam. The same technique has resurected strange LED dropouts and displays.

Cheers, Geoff


DeOxit: Best thing you can do for a Spice. Great stuff that really works.

WD40: Worst thing you can do for anything calculator related. The only thing it does well is to displace water. Every other aspect of the stuff is a disaster. Had a 42S once that got wet... rather than just take the batteries out and let it dry for a day, the owner sprayed WD40 into the keyboard. End of story and no, it was not a happy ending.


I agree WD40 should never ever ever be used for anything. If you think you should use some, don't. Wretched stuff.

Well, it is good for its intended purpose but nobody uses it for just that.

- Pauli


Tony Duell refers to the stuff as Wanton Destruction 40...


Yeah, I've seen lots of mechanical things utter ruined by this stuff.
Vile stuff. I never really though about using it on electrical stuff but I'm sure it would ruin that as well.

- Pauli


DeOxit: Best thing you can do for a Spice. Great stuff that really works.

Never heard of this stuff. How do you use it on a Spice keyboard?

- Pauli


Remove the IC's from the unit and soak overnight in a puddle of the stuff, it dissolves the oxidation. Reassemble.

Caig Website

PS: I initially thought the stuff was right up there with snake oil. I was wrong, it really does work. That's not to say I agree with all the claims they make but it does play well with calculators.

Edited: 15 Nov 2009, 7:42 p.m.


Thanks for that Randy. I didn't realise you were talking about the chips not the keyboard.

- Pauli


I misunderstood... sorry. Not much you can do for a plastic dome Spice keyboard that is intermittent. The problem is always a cracked metal trace that runs through the flex dome. With use, they fracture. Not something that is repairable.

This is why HP later redesigned the Spice keyboard with the metal snap dome design of the 41 - as it was a known reliability problem.


I have been using white distilled vinegar to disolve the green crud. It seems to work very well and not damage the circuit board or ICs. Does this stuff work better/safer/cleaner?


The only difference would be that it would not oxidize solder the way vinegar does. Oh, one other difference, a 25 ml bottle costs about $35 US...



WD-40, only good for displacing water! Had a friend "oil" a 200 year old Georgian Bracket clock with it! It stopped 5 days later. $560 dollars later I had it running.

DeOxit, must try it, does it preclude a mechanical cleaning and how harsh is it on the traces?

Cheers, Geoff

WD-40 in small (a drop) amounts is great for volume control knobs in vintage transistor radios though. Stops all scratchy volumes dead, a real fix!


DeOxit attacks oxidation. It's plastic safe and non-hazardous, non-flammable. Among other things, it's very good at dissolving/softening green corrosion on classic battery contacts without resorting to abrasion.


Thanks Randy,

I shall pick some up.


Possibly Related Threads…
Thread Author Replies Views Last Post
  HHC / HP Museum Programming Contest for RPN and RPL machines Gene Wright 18 5,575 09-22-2013, 09:39 AM
Last Post: Miguel Toro
  CLASSIC/SPICE KEY LEGENDS Mike T. 2 1,391 08-21-2013, 04:53 PM
Last Post: Mike T.
  RPN on other machines Palmer O. Hanson, Jr. 4 1,699 04-10-2013, 11:23 AM
Last Post: Palmer O. Hanson, Jr.
  HP Spice Legacy in the former CCCP (MK-61) Mike Morrow 17 4,581 04-07-2013, 08:25 PM
Last Post: db (martinez, ca.)
  Stupid idea of the day: 41-compatible watch bhtooefr 0 1,012 03-31-2013, 08:23 AM
Last Post: bhtooefr
  Repairing HP 65 Michae Altmann 5 2,047 03-15-2013, 04:13 AM
Last Post: Joel Setton (France)
  [41CL] Repairing an image in Flash Monte Dalrymple 0 891 01-24-2013, 07:01 PM
Last Post: Monte Dalrymple
  Book on repairing HP calculators? Dave F 24 5,953 11-23-2012, 06:46 AM
Last Post: Bart (UK)
  Idea for a 41C rom of "big" programs Gene Wright 7 2,417 10-05-2012, 04:29 AM
Last Post: Mike (Stgt)
  39GII -> 50G idea bluesun08 14 3,815 08-19-2012, 12:03 AM
Last Post: Dave Shaffer (Arizona)

Forum Jump: