Cleaning and Restoration: Good or Evil?


This may be a dumb question to most of you, but here goes:

Is restoration and cleaning a GOOD, or an EVIL thing to do?

I haven't really been COLLECTING, so much as using, and giving a home to, my calculators. But I have been exposed to you all for a while now, and becoming more interested in taking care of and having good examples of the calculator art, HP and others.

And it seems prudent to consider their worth to others in light of the collector market. I am starting to believe that, I too, am sort of a budding calculator collector.

So, anyway, a collector I know here in my town has a HP25c, and he loaned it to me for a day, and it was REALLY GRUNGY.

I had wanted to see a good example of the 25c for myself, and of course I fell in love with it, but wasn't pleased to see its state. It worked, it just looked very dirty and stained and hazy.

So that night, I "did him a favor": I, uh, well, I CLEANED it.

Okay, okay, I am a neatness freak, but I thought I was doing something nice. It is certainly a special calculator, very small and pretty and the "Continuous Memory" script on the front of the keypad, and so I was very careful and lightly went over and over it all completely with lots of cotton swabs and diluted Simple Green.

When I was done, I was proud: I hadn't messed up any of the painted legends, and it was much more readable, squeaky clean, and I thought it looked wonderful-- close to a "new" 25c. I KNEW my friend would be much pleased with the effort.

So, the next day. My collector friend acted a little nonplussed, like I had returned his calculator dead and smoking. He just grunted and looked mad, and left. Eek. And here I am, feeling really embarrassed.

Really I don't understand-- but would guess that I have somehow dishonored a previously unmentioned collector's code of conduct. Have I possibly hurt his calc by cleaning it? Why?

This has thrown me for a bit of a loop, since I am in the process of restoring a desktop calc of my own, and now wonder if maybe my plans are misguided.

What do you collectors think? Maybe dirt makes it more "vintage"? Would any of you like a grungy calculator BETTER than a clean one?

Is there something about cleaning and restoration my momma didn't tell me? ;-(


Your mother didn't restore calculators.

The HP25c machines are not noted for their robustness and I would be very reluctant to start putting dilute ANYTHING on them unless I had completely disassembled it.

These machines are an electrical nightmare and HP should have been ashamed about releasing them. When you look at the original classics, they were tough as nails. The woodstocks were not nearly the same quality.

I would certainly ask someone's permission before cleaning the machine. I certainly would not use simple green and water near anything electronic.....


Hmm, yes, Tom, I deserve the criticism of my cleaning methods probably as much as the philosophical aim, I suppose....

Having cleaned some of my own calculators before with the same dilute Simple Green and q-tip method, and taking care in cleaning his HP-25c the way I would have if it had been my own, I was not particularly feeling I had taken any risks. If anything, I was confident that I knew HOW to do it well. (And I am certain, if you had watched me doing it, any fears you have regarding my use of water/SimpleGreen near electronics would have been allayed. I used about 150 q-tips to do it, and nothing ever went where I did not specifically WANT it to go...)

But I certainly did not mean to vex my friend, either, and perhaps you have hit upon all or part of his anger; that it was a concern over HOW it was done, and that I might have ruined it FUNCTIONALLY.

And certainly, you are right that I SHOULD HAVE asked his permission to clean it. I know that now. I shall apologize to him for having messed with his machine in a way he hadn't supposed I would when he let me borrow it. I hope he can get over my insensitive error-- I like him as a knowledgeable fellow calculator enthusiast, and someday hope to make up to him for my blunderous ways.

I guess I wish further guidance about the very issue of calculator cleanliness, though, and what "the collector community" thinks is valuable aesthetically.

Vintage dirt and flaws, or a detailed return to former glory?

Did I ruin anything of the HP25c's APPEARANCE, from a collector's perspective, in cleaning it?

Let me mention that desktop calc I told you previously I was trying to 'restore'.

I happen to have, among other things, a very old and imperfect 9100A. It was stored for years in a closet, back when I didn't even know it was more than just a particularly bulky desk calculator that stored numbers and held them even unplugged. (It used to bow the top of my desk with its weight, so in the closet heap of equipment it went!)

Now I want my calculators to be "as new" and perfect as they can be-- and so I got some with power problems fixed, have been locating accessories and "doors" and such for others, and testing things out on them. And yes, I have been cleaning them. The one I have been trying the hardest to really get "perfect" has been the 9100a.

I have been going to the trouble, for instance, of contracting to have a "D"-shaped wheel cast in 70-hardness silicone rubber specially made for the card-reader to work again (I just found out the cost: will be nearly $100 by the time I get it); of locating some thin transparent green glass (from a stained-glass supplier) so I can silkscreen the X-Y-Z register legends slide that was scorched and melted... and trying to get a broken bakelite incandescent bulb sconce re-made (in ceramic, since no one seems to do bakelite anymore), and buffing small scratches out of the acrylic screen area, etc.

All this stuff is meticulous and time-consuming and a lot like restoration of an antique car to showroom status. (A Deusenberg collector wants his pride to be correct, driveable AND shiny; but an antique furniture collector would be silly to refinish and reupholster that beat-up LouisXIV chaise, even by using antique materials and methods--- a philosophical difference in the collector value of "visible age" as a determinant of authenticity and collectability. I guess I am following the Deusenberg collector philosophy...)

And, believe it or not, I was actually debating whether to remove and sand-blast the 9100a's cast-aluminum cover and then give it a fresh coat of HP-beige enamel paint, to replace the yellowed, scarred, chipped, sticker-goo-marred surface I got it in.

I am trying to do this restoration first-class. I want it to be both AS FUNCTIONAL and AS BEAUTIFUL as the day it was delivered to the original owner.

But if any or all of this hurts the value of the calculator to the collector, I need to know this-- so I know at least whether I am actually "restoring" my baby, or merely "customizing" it.

(Maybe I should paint it metallic purple with orange flame-stripes down the body, if all I am doing is wasting the value anyway).

Any collectors here understand what I am talking about? Would any of you be doing the things I am to my 9100a, or do you think I'm foolish to try? The merits of the cleaning method being excluded for a moment, is it simply better to have, as my collector friend had, a scuzzy calc with its original dirt intact?

As a FUNCTIONAL issue, I believe that most of you would do at least some of what I am trying to do, even if it wasn't just "stock". If not, wrapping cracked posts in 41 bodies and looking for a replacement for Katie's printer gear and people using model-airplane tubing in a card-reader just wouldn't come up. You try to make it as good as new, FUNCTIONALLY. Do you collectors have a view, though, that painting the 9100a back to its original color would be a mistake?



Being somewhat of a clean freak myself, I completely sympathize with your feelings. However, I've also been in the situation of borrowing other people's grungy calculators and have had to resist the temptation to clean them. It's not so much because of the potential of damaging them, it's just that some people like to keep them as is and some people just like them dirty. It's not too far a stretch, I think, to imagine that you sat at a messy co-worker's desk for a day and decided to do her a favor and clean it up!

Personally, I like to do whatever internal repairs are needed then carefully clean the outside of the cases. But I stop short of painting or otherwise retouching them, with one exception; I remove scratches on the lens and polish it. It's very easy to do, and goes a long way to improve the overall appearance of the calculator without much chance of damage.



You say you remove the scratches and polish the display. How do you remove scratches from the display?


I've had good results using plastic polish. This stuff is generally designed for automotive use, but works well on any plastic. I use the 3M brand that I buy at an auto specialty store.


I haven't come up with a really good way to remove very deep scratches. Surface ones and those that are not too deep I remove by (don't cringe) sandpapering out the scratch using #1500 ultra-fine silicon carbide paper (most hardware stores sell this) then polish it with Novus #2 plastic scratch remover (someone on ebay has this out there perpetually, along with the #1 and #3 stuff). You can skip the sandpaper for extremely light scratches.



How do you remove scratches from the aluminum bezel of the HP-11? The scratches are light but many.


I also use 1500 grit sand paper, and then I use SIMI chrome polishing compound. This stuff works great on plastic lens'.


Personally, I like the "metallic purple with orange flame-stripes" paint scheme - go for it !!


Thanks all for your considered responses. Tom, Katie, Jim, Todd, John; thanks for the guidance. No, the 9100a will NOT be metallic purple any time soon (but the "flame stripes" WOULD cover a nasty scratch... maybe-- naw). ;-)

Actually, instead of painting it, maybe I will check into the possibility of having that aluminum cover just professionally (steam?) cleaned. That way I could have a calculator that looks mostly new, but for standard wear/tear. I guess that is one sort of compromise that collectors make, mainly to preserve the value to other collectors.

But if you collectors and owners don't mind answering further probing questions:

If someone were to make NEW 41 or 71 or 75 port-covers for the ones you are missing, would you buy them? Or a new replacement red acrylic lens on your classic? Or a new integral battery pack/cover, for your woodstock with the missing one?

Or, if a small manufacturer could make replica Classic display-LED arrays, would you consider replacing non-functional digit elements with new but non-HP ones?

Would you consider it a fraud if you bought a 35 on eBay, and on opening it, found the display part was made in 2000 by Foobartronix Ltd.? Or would you rather have that than a calc whose third and seventh digits have missing bars?

If you had a box of three calculators of one model, all defective in different ways, who among you would take the good pieces from each to fashion one non-defective calculator? Should it wear the lowest serial number, or the one that matches the majority of the electronics, or does it even matter?

If someone showed you (with "Before" pictures) that they had repainted some faded legends on the face of their calc, and the job was so detailed and exact you could not differentiate between their restored legending and the best original, would you "count off" or refuse to buy that calc, or think they had done a Good thing?

If someone had invented a kit that "hot-rodded" a standard calc... let's say they invented a small internal board to connect into the guts of a Spice, allowing it to communicate with a serial-port-modified power pack, so it could upload/download programs from a pc via the charge-port connector (hmm, superimposed data on power, it would be possible, btw)-- so how many of you would modify a calc for a desirable quality like intercommunicability? Or does anyone view that as a sacriledge?

If your calc could be fitted with a much more capable/longer use-time Lithium-Ion power pack instead of the old NiCads, but meant using a different power brick than the one that came with the machine, would you go for it, or prefer to stick with the NiCads?

I'm going to say, for myself, I STILL answer all the above questions pretty unilaterally: I want calculators that work and act and look as new as they can, even including upgrading and so on.

I suppose that means I am NOT a Collector, as such. I can guess most of you will be wary of my kind. ;-)

I'd always rather have had HP continuing to make my favorites, so I could pick up a brand-new 41CX (or its rightful successor) at my local dealer ad infinitum. I would always buy second-sourced but NEW media over ragged original tapes, if it were available. And any means to repair and restore functionality to my old machines would get a fair look-- I won't EVER care to own a machine that doesn't scan several of its keys or display its results adequately, except maybe as "fodder" for parting out and repairing other calcs.

So how far do all YOU "real" collectors go in defining yourselves? Could I get a poll here? (Confidential if you pseudonymize). I just want to know your gut feelings about what you consider valuable or "essential" about your collection and the way you approach it...


> NEW 41 or 71 or 75 port-covers [...] would you buy them?


> a new replacement red acrylic lens on your classic?


> Or a new integral battery pack/cover [...]?


> replica Classic display-LED arrays

Aren't those still available from HP? In any case, my answer is again Yes.

> Would you consider it a fraud if you [...] found the display part was made in 2000 by Foobartronix Ltd.?


> who among you would take the good pieces from each to fashion one non-defective calculator?

I do that regularly. I consider it my sacred duty to bring machines back to life.

> serial number [...] does it even matter?

Not much; I try not to mix invalid serial numbers, e.g., I won't put a Woodstock back with a 1975 label on an HP-29C. Or, I won't but a 1979 back on an HP-97 that has the early version's SIN bug.

> repainted some faded legends [...] they had done a Good thing?


> If someone had invented a kit that "hot-rodded" a standard calc...

Not for me, thanks. I'm after these calculators the way they were. By way of analogy, if you have a vintage Ford Model-T, there's a huge difference between putting new sparkplugs in, or replacing the engine with a computered, fuel-injected modern unit.

Note that I am not against modifications that are of the same vintage as the calculator itself. E.g., an HP-45 modified with a quartz crystal is okay with me. In fact, I even have the right HP-45 (somewhat battered, but working fine) for this purpose, I just can't find a darn crystal with the right frequency.

> fitted with a much more capable/longer use-time Lithium-Ion power pack

Fine with me, since batteries are consumables anyway.



glynn; sorry, but i'm too lazy to itemize my answers. i also believe that calculators should operate, whatever has to be done to them (or be used for parts). so i guess my answers would all be the same as yours. my 21 looks like its got a frankenstien bolt in it's neck thats a new plug for a 220 source (when in la paz, do as the paceneos), but it works fine. im glad there are collectors but to me; my 41's are the best tool for the job, no more. whatever works...


"I'm going to say, for myself, I STILL answer all the above questions pretty unilaterally: I want calculators that work and act and
look as new as they can, even including upgrading and so on."

I would not want most of the modifications you mentioned. The exception might be the "hot rodded" calc that I might want IN ADDITION to a real unmodified sample if I wanted to use its new functionality. (I wouldn't mess up a calc like that myself though unless it was a very common model.)

100% functional all original, good looking calculators are not that hard to find. If I get stuck with one that isn't, I can always sell it at a profit on ebay.


My solution to all your questions is to concentrate on working, all original mint to near-mint calculators. When I acquired anything else I always wanted to replace it with something better anyway. I would consider it fraud if someone was knowingly selling calculators with new LEDs on eBay without revealing this in the auction listing. (Same thing goes for an expensive Swiss or vintage American watch with a quartz movement inside.)

However, you should approach this in whatever way makes you happy. I have purchased some old plastic kits from the 1970s and… gasp!… built them. For those that don't know, building a kit lowers its collecting value immensely. However, I wanted built kits - not an investment in plastic parts. Likewise, some people have their watchmakers install quartz movements in their old wristwatches to make them more reliable and accurate. This can change the value of a watch from thousands to tens of dollars but some folks just want to know the time.


I started "collecting" HP calculators when my trusty HP-42S started having an intermittent "9" key. The 42S wasn't my first HP (I used to have a 41CV, which for some inexplicable reason, I sold when I was in grad school). Anyway, I e-mailed all my co-workers to see if anyone had any old HPs lying around, and got a reply from the company president (who was also my grad supervisor years ago) that he had not one, but three HP calculators that (a) he no longer used, and (b) didn't work: an HP-19C, an HP-21, and an HP-41CX. He wanted to keep the 21 for nostalgia reasons, but _gave_ me the other two.

The 19C required a bit of work to get working again: new battery pack, cleaning of contacts, fixing some broken wires, repairing the battery hatch (someone had broken off the tabs). After that, everything worked except two pixels of the print-head don't work. I attempted to repair that with conductive paint under a microscope, but was unsuccessful. Other than that, the calculator is in good working condition. I didn't do much cleaning because it wasn't really all that dirty.

The 41CX required more work. If you search the Museum, you'll find my article on repairing it. I think the work I did on it would definitely be considered blasphemy by some of the more picky collectors. But it is now in perfect working order, and looks nearly new.

Since then, I've bought a few HP's on eBay too: a 32E and a 34C. The 32E was working, but EXTREMELY filthy and smelly. I completely disassembled it, washed all the plastic parts in soapy water, cleaned the corroded contacts, made up a new battery pack, and put it all back together. I did not fix a missing bit of plastic along the bottom edge of the case, and I did not touch up the lettering around the on-off switch. It is now in perfect working order.

The 34C required more work. It was one of the ones where the chips were held against a flexible circuit board by a plastic frame, and like many of that construction, it wasn't working. It was also filthy, and the internal mounting posts were cracked. I completely disassembled it, cleaned all the plastic, repaired the cracked posts, and then (gasp) ... carved away plastic from the chip-frame to allow more room where each pin contacts the circuit board and surface-mount-soldered all the chips to the flexible board.
The result is a nearly-new looking, perfectly working HP-34C.

You may notice a common trend in all my calculator restorations: "perfect working order". My collection doesn't sit in a drawer. At any given time, at least two or three of the calculators are in circulation. The HP-34C is on my desk (I do a lot of model airplane and electronics design work). The 32E is on my workbench where I use it when calculating things on the spot when building airplanes and circuits.

The 19C gets used the least, because it's so large, and doesn't do anything one of the others can't do. The 41CX gets used a fair bit to do more complex things the 34C can't do. I still use the 42S occasionally simply because I have some programs in it that I haven't bothered translating to one of the other machines.

I would say my most-used calculator is the 34C. It certainly isn't mint, and if I were ever to sell it (or any of my collection), I would disclose all work I'd done on it. But if I hadn't done the work, the calculator would be grungy and non-working, and I don't see the point of having it then.



stefan; i think i know what you mean.
when i was a kid i once asked my dad where he got the old worn-almost-out 3 blade pocket knife that he always carried. he told me that my grandpaw sturm (moms dad) had given it to him. i said that he should probably put it away and keep it safe because it was soooo old (mabye 20 years!). he told me that it wouldnt mean much to him if he couldn't use it. thats how i feel now about using his old plumb wrenches and my 41. he eventually wore out that knife and i've split a couple of sockets (and dinged up the hp). it's that some tools just work better...



I could not agree more. When I attended college (circa 1878), some classmates treasured their HP25, only bringing them to class for final exams (sort of a magic token, since they were not familiar enough with them, they hardly know how to program them).

As per myself, I literally used my HP25 always, risking it to fall over a flight of stairs (once, it survived), wearing off some of the lettering and, finally, lending it to a friend from whom it was stolen. I miss it a lot, but while I had it, it was used 110% !

I was a little more cautious with my HP41C, always used it with an overlay to protect keyboard legends, but otherwise opened it, studied it, interfaced it... When battery contacts corroded, I soldered (very carefully) two wire wrap wires to secure power from the batteries, and when the card reader failed, I replaced the roller and soldered loose magnetic heads wires. It is preferrable to have and use these useful tools than just to adore them. And careful use is not incompatible with good cosmetic state.

Now, if some of my '78 classmates still have one of those mint, never programmed HP25...


Thanks all who responded. I have to admit I am both surprised and pleased. I thought I might get a lot of responses which, without so much saying it, might have suggested my approach to calculators was way out of line.

Now as I see it, there ARE, as Jim stated, a few different philosophies, and yet I am seeing they co-exist pretty well. Even my own attitude is getting more "moderate" now that I see that "too much cleaning" and "too much restoring" are possible, too.

I apologized to my collector buddy for attempting to clean his calculator... and he agrees totally with Katie, too, that some folks just prefer them dirty, and that I returned to him a calculator he could not even be sure was HIS. Ooops. I now see where my thinking I was doing a cool thing was just not thinking of him.

I will always like my own calcs clean, but I will keep those activities strictly to my own collection... ;-)


It's a personal thing.

In all collecting fields I know, there are people who want the item "as found", others who want it "clean but all original" and others who want it to be "as new even if that requires modifications, unoriginal parts, paint etc.".

The middle group seems to be most common, but the first group is very firm in their beliefs. The last group breaks down into people willing to make repairs for cosmetic vs functionality reasons but both seem to bug people in the first groups.

A lot of the HP’s I’ve seen have become shiny from too much cleaning so be careful.


Since we've broached the topic, does anyone know how to get rid of smoker's smell in a calculator? Some calculators I've acquired were previously owned by smokers, and the ciggy stench has permeated the calculator leaving it with a pungent aroma! I've had fairly good results with smelly manuals just letting them "air out", but is there a faster way to "de-smoke" a calculator?



Hi Todd,

I use some stuff called Citra-Solv that I found at the local Food Emporium. It works great for getting rid of tar and most glue residues. I've cleaned the cases of several smokers' calculators with this and it's totally amazing how much tar comes off! It'll get rid of the smell completely, but it leaves its own orange peel smell behind. That'll dissipate in a couple of days or you can clean it off with whatever you normally use to clean calcs with.


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