28C corrosion

On way into work today, I saw some people setting up for a garage sale. I stop and asked if they minded if I looked while they were setting up. I came across a HP 28C calculator that was for sale. It was marked $30. I tried to turn it on, but it did not come on right away. I fiddled with it a bit and it finally came on with the message Memory Lost. I ask the guy if he would sell it for $15, and he said sure because it only worked some of the time. I took the batteries out and I saw why it only worked some of the time as there was white powder on battery from some corrosion. I figure I could fix it.

Since battery compartment is strange for the 28C, what is the best way to get the corrosion out of there. I would think that a paste of baking soda and water would help neutralize the buildup, but moisture may get into case of calculator, and I don't think that would be a good thing.

Has anyone dealt with this before, and if so, how.


It's never too easy, but most leaked electrolytes are water soluble and while they may either be decidedly acidic or basic (alkaline), there is no real need to neutralize it.

I just take a wet but not dripping piece of paper towel and take my time with wiping out the crust. It should dissolve. But be sure to get the stuff stuck in corners, cracks, etc. A toothpick may be soft enough on the plastic and hard enough to dislodge the leaked material.

Also, be sure to wipe the metal contacts as clean as you can with the wet paper towel.

And for the sake of the metal, visibly dry the battery compartment well and then leave the battery door off and let the compartment dry for at least several hours or overnight.

If you are worried about the corrosiveness or toxicity of the leaked chemicals, you can wear thin rubber gloves, but that's not really necessary- just don't eat the stuff and wash your hands afterward!


If you are worried about the corrosiveness or toxicity of the leaked chemicals...

I'm not so worried about that with my hands or the like, but I would think I need to neutralize the chemicals so they do not continue to crud up the metal in there, or have you not had issues with that?

Thank you again Ed!


No real need to worry about that- it's like the argument with antibacterial hand soap, whether it's really necessary. The real answer is that it's not, for washing away germs is as good as killing them on your skin (and let's not even go into the whole issue of antibiotic resistance).

Besides, you can't really determine exactly how much dried electrolyte you have in the battery compartment, so you may respond with too little or too much base/acid (depending on whether the electrolytic paste was acid or base) and you then have the same problem again.

Most of this stuff is at least moderately soluble in water, so wiping away with a wet paper towel, then finally wiping with a good clean wet one, before drying is all you need. But water is corrosive for most metals, especially ferrous ones, so drying is very necessary.

And in the future, if there is more crud, it means that either your new batteries are leaking or there is stuff from behind the battery compartment you couldn't see the first time, which would require the more radical step of performing calculator surgery and opening the case.


...which would require the more radical step of performing calculator surgery and opening the case.

And from looks of case, it does not look like it would be easy to open. In fact, I don't see any clues as to how it may even be opened.

Okay my friend, I will try your method and report what happens. For $15, I can't complain.


I'd use 'just-damp' cotton buds (erm sticks with little cotton balls on the end?) to swab out the battery compartment - they just have the reach. Careful they dont shred though...

Hope this helps



Every person with an HP calculator in their collection should treat the battery terminals with DeoxIT® GOLD or similar product from CAIG Industries. I treat my calcs with this to prevent corrosion.. very effective. -- Apply it with one of the 5-6cm lint free brushes you can get from the same company.. don't mess with cotton swaps and baking soda.

Edited: 9 Aug 2007, 10:27 p.m.


Where do you find this stuff?


On their website

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