Mouldy calc


I have an hp55 that was certainly kept in the wrong place by its previous owner so now it smells very mouldy.
After a bit of work, it is now quite clean and working properly but the smell is unpleasant. Does anyone know how I can get rid of it without damageing anything.
Here I am talking not only about the calc but also the case, charger, manual, slip case, reference guide...

Any idea will be welcome.

Thanks a lot,


PS: Does anyone know of a website that has instruction about how to properly clean and restore books and cardboard boxes?


Hi Arnaud,

I've heard of people using Ozone generators to eliminate smells in cars (such as after hitting a skunk). I wonder if it would help with a smelly calculator?

Does anyone know if ozone would harm any of the calculator parts? Not exactly sure how you would do it - I know you don't want to breathe very much of it. And, of course, where do you find an ozone machine?

Last year I aquired a bunch of calculators with their manuals from an estate and they had been stored in a heavy smoker's house. They smelled like they had just come out of a house fire. Forturnatelly, after several months of fresh air they have lost their smokey smell.

Hopefully, yours will fade with time also,



Store with baking soda or charcoal briquets. Both have odor eating abilities.

The Library of Congress has info on care and repair of paper products. The Gemmary has archival materials.


Arnaud, it is best as they have said, to just let it continue to air out, and if you like, use baking soda or charcoal to try to absorb some of the odors to hasten the process.

But don't mess with ozone; it's an oxidant. In other words, it may cause corrosion and other adverse effects in something so sensitive as an electronic circuit with fine connections and joints, like your HP 55.


Hi Ed,

"But don't mess with ozone; it's an oxidant. In other words, it may cause corrosion and other adverse effects in something so sensitive as an electronic circuit with fine connections and joints, like your HP 55."

Good point. I just did a little more search on oxone and can only find references to using it to get rid of smells in clothes, furniture, car interiors, etc - but no reference to using it with electrical gear. They also advise that ozone will "eat" organic material - so excess use would damage natural rubber, wood, etc.

I agree - ozone mught not be a good idea.




And, Ozone will eat your lungs.


Hi Bill,

"And, Ozone will eat your lungs."

Several years ago, I ran across a Book at an Antique Store titled: "Air Conditioning and Ozone Facts", published in 1939. Since I'm in the field od HVAC design, I had to buy it. The first two-thirds of the book is about the state of the art (at least in 1939) of Air Conditioning - but the last third is the most fascinating. This dealt with the use of Ozone Generation in the ventilating systems to "purify" the air and to have the "oxygen content increased". Also discusses using ozone to purify drinking water in European cities, sewage treatment, swimming pools.

The best quote is "The author, in order to disprove the theory often advanced in recent years that ozone is a poisononous gas, installed in his home in October, 1934, the ozone generator shown in Figure 59."

I did a search for the author on the web and can only come up that he authored this book - no other data concerning his research or the results of his test using ozone in his home...........

Sorry for the off topic subject.


12345 to delete


I don't know about electronics, but optical goods stored in damp conditions often grow fungi on inner surfaces, and if the surfaces aren't cleaned the fungi will eventually etch the glass. Washing surfaces with household ammonia and then acetone will kill the fungi and remove traces from the glass, but they would probably wreak havoc on electronics.
Isopropyl alcohol 91% (not the 70% stuff in the medicine cabinet) commonly used to remove flux residue from PCBs might kill fungi too without causing more harm.

Ozone is useful sometimes. I put an ozone generator (that makes ozone by flowing air around a strong ultraviolet lamp) in a hot tub system, and it keeps the water clean without forming chloramines (carcinogenic compounds). Ozone generators are used similarly in swimming pools ,more commonly in Europe than the US.


Thanks for all your help!
I guess lots of sun and fresh air will be the best cure. My only problem is that I live in a North facing flat in England. So it will not be easy.
Also, my landlord put a microwave oven in the flat that I believe is as old as my hp55 and it regurlarly makes electric arc that are a nice show and generate ozone. I may just put an old book in there see what happens...



Hi Arnaud,

You might want to check that microwave for radiation leakage.

Especially in a small flat. You can buy little stckybacked microwave dosimeters.




Hey Gentlemen!

Don't even bother with measuring the microwave emissions; if it's so old it arcs when you use it, I'M PRETTY SURE IT LEAKS MICROWAVES, as shielding in early models were poor and over time, it just gets worse.

If he won't replace it for you, get your own (they're pretty good and inexpensive these days) and stick his under the couch or in a closet somewhere.

As to ozone, Bill is right. On the surface of the Earth, it is considered by all rights to be a pollutant. It is an oxidant and so will cause chemical (hence, tissue) damage. It's good only in the upper atmosphere!

And Arnaud, I feel bad for you. As the rest of you, I am a HP calc nut, and years ago, I had to throw out my disintegrating case for my 34C. It didn't smell, but had a similar effect: the polymers of the inner lining was crumbling into this oily feeling powder (only later through this board did I realize you could simply wash it out) and bothered so much I got rid of it. (Fortunately, someone had an abandoned old 45 brown case that is still good lying around, so it's in that nowadays.)


I have experience with Ozone use at home. We have several ozone generators, for air-freshening and for medical treatment. Ozone is very useful for treating mold and smoke damage, but as pointed out by others, can damage organic parts.

Ozone is a molecule consisting of 3 oxygen atoms. It is rather unstable, and easily gives up one oxygen atom, reverting to O2 (ordinary oxygen.) Organic molecules often greedily mate with ozone to become oxidized. Mold is particularly susceptible. Smoke particles, which are the results of incomplete combustion, oxidize into harmless CO2 and other particulates which fall out of the air. Rubber loves to combine with oxygen, turning into a slimy mess. (I lost the spark plug wires in a car I was trying to de-smoke.)

Small amounts of ozone in the air are harmless to humans. The fresh smell after an electrical storm is caused by ozone naturally generated. Ozone is preferred over chlorine for water treatment in many countries because once it does the work, the resulting oxygen is harmless. Ozone can easily be manufactured from room air or pure oxygen.

I would not recommend using ozone to treat the calculators. Sunshine kills mold, though may age plastic. Cleaning with baking soda and/or activated carbon will be less effective, but far less likely to damage the calculator.

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