Good thoughts! I'd suggest a few points:

*Before* you put in the batteries, be sure you know which way they are supposed to go in. Putting them in backwards could destroy the innards, if the calculator isn't designed to allow that. (Reversed batteries definitely will destroy a diode in an HP-48, and opening up an HP-48 is not at all casual.

(See the HP-48 FAQ; there are probably some comments there. Go to www.engr.uvic.ca/~aschoorl/faq/ ) (Yes, that is "schoorl"; he's been tremendously helpful to the HP-48 community)).

Try scraping as a last resort, if there's any likelihood that you'll be removing a layer of electroplating intended to protect against corrosion.

Electroplating thickness, for gold, at least, is measured in microinches or micrometers--very thin! For instance, a brass (or steel) spring might be plated with nickel. In the short term, you'll restore operation, but you could risk accelerated corrosion, long-term. However, some contact springs (not so often for batteries, but more likely in external-power connectors) are made of corrosion-resistant alloys.

Consider careful use of a contact lubricant, which can protect surfaces against corrosion, and help maintain good connections. Except for switches with metal contacts, the lubricating properties are incidental. There is a costly substance that has been sold under the tradename Stabilant-22 that enhances conductivity of connections. Go to a good home audio store to get some, and be prepared for a stiff price tag. Don't expect it to necessarily do wonders if there are no other signs of life.

When it comes to collapsible-dome contacts, it's safer not to use sprays that contain solvents. The black button is electrically conductive, and is likely to be made of a carbon-loaded elastomer. (Elastomers are "springy" materials that can be stretched and will regain their shape; rubber is the best known, but lots of elastomers (especially foam) are not rubber.) I'm not really qualified to recommend much; cleanliness is quite important, though. Do *not* scrape the interdigitated contact-finger patterns!

Corrosion protection is very important. I'd say that Stabilant-22 probably doesn't belong here, nor does lubricant.

Spray contact cleaner really ought to do some good, but be careful so that it goes only where you want it to. Better to apply it with a swab than its by using its own pressure; you get better control that way. Try Radio Shack, in the USA.

Especially with calculators that have internal multi-pin connectors, contact cleaner and lubricant should do good. Move them back and forth a few times before the cleaner evaporates.

Opening up handheld electronic devices is a whole topic in itself.

One helpful little secret is that a screw might be hidden underneath a label. Removing the label without defacing it is a real art, in my opinion.

I'd say that you need to find a solvent that will soften the adhesive, but not attack the label nor the plastic of the housing. (It would be nice to have an organic chemist friend!) Then, you'll need to reattach the label with an effective adhesive that holds, yet permits future removal. (Rubik's cube sticker experience can help! Btw, don't rearrange stickers. Disassemble a cube (no tools needed), and reassemble in the solved state.)

Another matter, which is *very important*, is knowing how to replace the screws! But first, a few words word on removing screws. If you have a worn cross-recess screwdriver (Phillips, in the USA (and Europe?); Purasu (?) in Japan), at least try grinding off the point (you could use a sharpening stone, but don't create a groove). Much better yet, invest in a very good set of screwdrivers. Worn cross-recess screwdrivers should be saved for their tool steel...

Any well-designed device will have screws all of the same length. Once you remove your second screw, compare its diameter and length to the first. Keep comparing, and make a sketch for any exceptions. Remember that cats love to see how quickly they can hide those things that look like peculiar bugs.

When you remove a screw from a plastic structure, unless the plastic has a molded-in metal insert (or some other metal part), the screw will have special threads. They are "high" and "narrow", spaced quite far apart, and sometimes are made with alternating smaller and larger diameters.

Keep in mind that when the screw was first inserted, these narrow threads deformed the plastic to create mating threads in the plastic. The slight springiness of the plastic ensures a good grip.

Here's the important part: When you replace the screws, try to remember to re-use the threads in the plastic. If you don't, after a few insertions, the plastic in the hole will be shredded, and the screw won't hold. Push the screw gently into the hole, and turn it backwards while pushing gently inward. You should expect to feel a bump when the threads align. Only now should you tighten the screw. Experience and judgment will tell you how tight it should be. (For those with really-big tool budgets, there are torque screwdrivers!)

It seems that the majority of housings have latches to hold them together. These are structures unique to modern plastics that resemble, in their geometry, an ordinary room-door sliding latch bolt that lets you push the door closed, but which also keeps the door closed. Latches are really great for housing designers, because they are "no-cost" features that allow housings to be snapped together really quickly. Properly designed (they almost always are), they hold really well. Compared to a latch bolt, there are no moving parts, they don't stick out as far, the angle is different ("flatter"), they are much "wider", and depend upon the spring quality of the housing material. Assembly creates a temporary harmless deformation, just before the snap.

It also seems that some latches, maybe many, can be disassembled with minimal harm, so that they can be reassembled successfully. However, ** I could be very wrong on this point!** Comments welcome!

I'm not an expert at releasing latches, but fooling around with junked housings can teach a good bit. You can sometimes press inward at a gap between housing parts to help disengage a latch. Sometimes, a latch doesn't seem to be damaged by brute-force separation. A tool like a table knife, with a rounded edge, could be quite useful. Consider getting a Macintosh computer "case cracker" tool. It might be very useful.