New (to me!) HP-25


I'm happy to report that I've just picked up my first Woodstock, an HP-25, at a flea market. It's in very nice cosmetic condition, except for some bubbling and loss of black paint on the metallic "Hewlett Packard 25" label on the front.

Unfortunately, I bought it purely on faith, without checking the battery compartment. Why? Well, because I can't open the damn thing. The pragmatist in me says that this is because it's sealed shut with horrible battery decay. The optimist in me says that I'm just too much of a doofus to figure it out, and probably it's fine inside.

So, can anyone help this sad sap out? How do you get into the battery compartment? I see that there's a lovely thumb area, with a helpful arrow, but try as I might I can't slide the darn thing.



It was/is never easy to slide the battery compartment open, but what I do is wet my thumb so that it is "sticky", apply firm pressure in the direction of the arrow, but while doing so, you have to "encourage" the tail end of the compartment to rotate up, out of engagement with the housing. Your thumb push is trying to get the compartment to pivot at the arrow.

Takes some practice - I've had 30 years!



I see that there's a lovely thumb area, with a helpful arrow, but try as I might I can't slide the darn thing.

This is not a good sign, I'm afraid... I've encountered that once with an HP-21 and it was due to the fact, that the batteries had grown in size due to leakage and corrosion (that had spread through the whole calculator).
If you can't get the batteries out with "thumb-force" alone, pull out the rubber feet and unscrew the screws, that are underneat them. Thereafter, you can open the calculator and remove the batteries without applying brute force.

Good luck with it - the '25 is the nicest of all HP calculators!

Greetings, Max


NEVER connect the charger to it until everything has been cleaned and tested. In fact, you should never connect the charger to it, period.

Bad battery contact, bad cells or corrosion of any kind will leave you with a fried 25 if you connect the charger.

Once you get the old battery out, test the unit with a bench power supply before going any further.

PS: I think you'll just need to remove the screws to get the thing apart. They are under the top feet. Remove, then push the circuit board out by using a small screwdriver or whatever to push the charger pins into the case, this will pop the top of the keyboard out so you can remove.


Thank you for the suggestions!

I was able to open it up, and indeed there is quite a bit of battery leakage inside. The traces and ICs seem to be in good condition, though. I think this is a completely salvageable calculator.

I've fixed several 41Cs and a 35, so I'm going to try some of the same techniques here. Gentle cleaning, washing away the alkaline battery gunk with vinegar. Then I'll test it with a bench power supply to see if I can get some life out of it.



The traces and ICs seem to be in good condition, though.

Alas, I spoke too soon. There was a decayed foam pad directly under the battery contacts, and when I took that out I found broken traces underneath, on the keyboard assembly.

I cleaned the components off with vinegar and warm water, and now I'm letting them air dry. I won't be able to test it further until I've fixed the traces, so it might be a while. A project for another day :)


I found broken traces underneath, on the keyboard assembly.

Bummer. Chances are the keyboard will be beyond repair as once the electrolyte gets into the key switch contacts, it is usually game over. The foam pad you mention was actually a piece of thin fiberboard which was to prevent battery leakage from getting into the unit. I wouldn't bother with repairing keyboard traces until you know that it works...

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