33C <clear button> repair

I have a trusty old 33C circa 1981 that I still use at work. It has deveoped a problem with the <clear> CLx button, the CLx button feels the same as the other functioning buttons, but appears to have lost contact sensitivity. Is there a way to remove the back panel and effect some type of repair to the button contact? I understand that the buttons are over some form of "bubble" pad, and not actually a mechanical type switch. True? If so does anyone know how the this contact can be improved, or is it toast?

First things first though, I tried to remove the back cover (two scews in battery compartment -top), but the attachement at the bottom of the two panels is solid/tight and I am afraid it will just bust apart if I try to pry it open like a clam shell. Is there a special method of doing this?
I really want to keep the old 33C working. Any help or suggestions for repair to improve the button contact would be appreciated.

B.C. Canada
Enter >=


This has been much discussed in the past here, a thorough search of the Forum Archives should yield some information. There are several methods for opening Spice series calculators. The most basic and brute force method (as noted in your post in the Articles Forum) is to just pry the case halves apart. To answer your question, it opens like a clamshell. It takes a lot of force, and when the case finally separates, it does so with a loud "crack" that is quite disconcerting. Therefore, others have developed alternate techniques. One is to "squeeze" the cases apart. I could not find the post where this was described in detail, but it involves putting your thumb on the lower edge of the front of the case, your fingers in the battery compartment, and squeezing. Another technique involves the use of dental floss, described here:
Regarding your button contact question, there are two versions of Spice internals. One type implements the keyboard contacts via plastic domes, the other has metal domes. See David's post below for cleaning instructions for the metal domes. I believe that the sheet with the plastic domes of the other version is also accessible, so it should be possible to clean the contact surfaces.
Good luck with your repair.

Edited: 30 Sept 2003, 12:30 p.m. after one or more responses were posted


Hey Jeff,
Thanks alot for your response. The methods for opening the 33C are especially helpful. I've had that unit for over 23 years, hate to kill the old dog needlessly. I have to admit the tightness of the attachment is a little daunting.

I guess the button contact design will reveal itself once opened. I'll have to do a search on the archives for button/contact repair. If it is the plastic bubble type, I assumed that the lost contact was due to a 'stretched" out bubble dome, and then not likely repairable. However, this is a great site, a lot of expertise here, so I am sure someone has devised a solution or have some useful ideas.

I was surprised to learn from this site three things; 1) that all these old HP calculators have such a strong following and retain an "antique" value; 2) that people still use their old HP's everyday and I am not the only one; and 3) that HP has fallen so far behind or forgotten about the hand held computer market.

I was going to buy a new scientific HP calculator at my local "Staples" store, but the unit did not even have RPN! I checked the HP website and found they only have around 2 scientific models to choose from. I guess I have not stayed tuned to the calculator market for quite a few years, since I've alway been using my 33C, but I just assumed that with the advancment of digital electronics over the last 23 YEARS, that HP would have had made a quantum leap by now in this market. Must not be a market with a huge return on investment, but you would have thought that just for the purpose of SELF RESPECT as a company, HP would have thrown a few $ at maintaining their lead in the hand held market, if only as a marketing tool for the rest of their computer electronics line, ..or even if it was just for nostalgia purposes.




Your last paragraph will resonate at the 99.9% level with most of the inhabitants of this site.

We all, too, use our beloved HP calculators daily and can't understand why HP has pretty much abandoned us. There is some hope for a couple of new calcs, but we're all stuck in the heyday of the 20-year old models!


Yes, and I count myself as one of that majority, but the economy and manufacturing realities have changed, though I suppose that could just be an excuse for the obvious shift in "philosophy" which came in with the change in the leadership of the company.


The spice series never used the strip switches. They were either the plastic bubble keyboard type (compression machines) or the dome switch type (soldered machines) like used on the woodstock or HP41 machines.

The dome keys are easily cleaned. There is a feedthough hold under each key. You clean the key by making a tiny wire brush out of three wire brush bristles in a pin vise holder. Place a drop of alcohol on the hole, dip the wire brush in more alcohol, and then gently scritch around in the key hole with the wire brush. The problem with the spice keyboard may be that several of the key holes are blocked by the soldered down 40 pin chip.


Tried to pry the back cover off my 33C. NO WAY is it coming off. The bottom attachment of the two halves is secured like it is SCREWED down. It will snap off for sure if I try to open it up like a clam. Tried pushing it together to unsnap a hook, tried twisting the two halves gainst each other, nada. Not willing to risk ruining the calculator. I guess I will just have to turn my calc on and off every time I want to clear the stack..

Thanks for all your help anyways guys.




It is actually possible to finesse the back off of a Spice calculator. After you've done it once, it gets easier. However, with just the back screws loose, you should be able to peek in there and see which type of unit it is and whether or not it is worth proceeding. The solderless ones have a beefy plastic backbone. There should be pictures somewhere on this site showing the differences.


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