How to dry out a 42S


My 42S got a rainwater bath in the car 'cuz stupid me left the window down. Completely soaked it (keyboard side - of course!). I took the batteries out and let it dry for a day. It seemed dry so I tried it - aghhhh - completetly dead. Batteries are okay.

I looked for help on trying to get it open - it didn't seem like a good idea! I thought maybe any moisture at all could cause problems with the CMOS guts....

Anybody have suggestions of what to try next?



It might take more than a day to dry it out. You can also try a hair dryer to speed up the processs, but be careful not to get it too hot.


Thanks. I put it in my utility closet with the boiler. It's about 90-95° in there. I was going to give it a few days before I tried it again... Hopefully the conductivity of the water wasn't enough to do any damage. I sure would hate to lose this puppy. First my 25C croaked with funky result errors, now this! Sigh.


This may sound strange, but I have heard of using rubbing alcohol to dry out electronic parts. You flush away the water with the alcohol and then the alcohol dries/evaporates much faster. My only concern with this method is not knowing whether any of the painted parts could withstand it.

Has anyone else heard of this method before?


I have had to fix a couple of HP42 units that were flooded and soaked in mud for several days. I ran them through three cycles of distilled water in an ultrasonic cleaner, then dried them out for a couple of days in an oven on LOW (like less than 140 F). Came back to life with no problem.

Alcohol may stain the keyboard background or cloud the plastic over the display, but I have used it in dire situations.


Dave, since you've had the good forture of repairing some 42Ss - Can you tell me if they can be opened? That is, in a reversable way. I'm not ready to call it dead yet as it has only been about 36 hours of drying time. But I figure if I can open it and get all traces of moisture out of the keyboard membrane and pc card I might have better chance than leaving residue inside.

Any chance?



It is not easy, but look for articles by Paul Brogger here at the MoHPC (Articles Forum)


I know this seems like a step in the wrong direction, but it might have been a good idea to flush the unit with distilled water before drying it out. Even rain water has things dissolved in it (heard of acid rain?). I guess I wouldn't do it now that it is almost dry, and it was rain water which should have less stuff dissolved in it than tap water. Take a close look at any exposed internal surfaces, such as inside the battery compartment, for signs of corrosion that would indicate the water was contaminated.


Paul Brogger's article is the best source of opening the machines. It is semi-reversible. Once closed back up the machine can be easily re-opened... sometimes too easily. It sure beats the method of prying off the keyboard bezel... which will always get messed up in the process.

The HP42 and HP48 series machines were never designed to be serviced. If anything went wrong, it went into the trash at HP. Also, there is very little inside them than can be repaired anyway. The main chip is permanently attached to the CPU card. There is a RAM chip and a few discrete parts (they almost never go bad).

The keyboard is also heat staked to the case (like the HP41). Taking it apart is almost sure to cause more problems than it fixes. I have used to distilled water/ultrasonic cleaner/oven trick to bring a couple of otherwise dead machines back to life.


I am a field surveyor and have dropped my 42s in water several times.

The best way I have found to remove the moisture is to place it in an airconditioned room overnight, then replace batteries.


I think that these people may be able to help!


I heard on the radio today of a woman charged with child abuse because she had hidden a gun in her microwave oven (for safekeeping) and then a child (I think her grandchild) turned on the oven, causing the gun to fire and (at least) injure the child (maybe worse).


You are all encouraged to try CD-ROM discs and glass "ball" Christmas ornaments. The metal layer gets quickly (but not instantly) eaten up by a beautiful, crawling array of blue sparks and arcs. Really impressive (and inexpensive) home entertainment!


Hmmm, now that is something those AOL disks would be good for! I wish they'd go back to sending the floppies, those were much more useful...


Finally! something to do all the CD's that come in the mail!


This has been a message from the Department of Redundancy Department.


I love it - tried several AOL CDs already. This really does make a great light show. Even my wife (another astronomer), who often takes a dim view of such "experiments" was impressed.

So far, I've only had the nerve to run the microwave for 4 or 5 seconds, which pretty well fries the CD. Anybody have a feeling for how long you can really run run the oven before the magnetron gets tired of such shenanigans? I think modern microwave ovens are pretty robust, but at some point all that unabsorbed power (actually, the CD is probably absorbing a fair amount) goes back into heating up the tube.

As near as I can tell, this may be the REAL reason that both microwave ovens and AOL CDs were invented!

What else should we be frying?!



You can run the nuke-o-matic for quite a while as long as you keep a cup of water in the unit to act as a load. You should never run a microwave empty (or almost so)... it is very hard on the magnetron.

There is another microwave trick that involves the use of a burning toothpick or match stick to make ball lightning. I had it explained to me a while back, but was wearing beer plugs at the time so I don't remember the details.


Ahh. Magnetrons and beer. Sounds like a recipe for disa-- erm, an interesting story. :^)


Yeah, but if you put the water in there, it may absorb all the juice and the AOL disk will just sit there, dark. Not as much fun.

I suppose neither of these (cup of water or AOL disk) is a good 50-75 ohm free space impedance match - but what is the impedance of a baked potato, and what (mis)match does the magnetron expect/survive?

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