how do i give a 25c a bath?


i found a 25 c at the flea but it was stored with the battery in it. sad. there is green spooge on the pcb traces. i am not sure if this is connected but; half the keys are stiff or unmovable too. i have little hope for it but i'd like to clean it up anyway. i think i remember someone saying a vinegar bath will neutralize battery stuff. is that ok? is there anything else i should bathe it in before, after, or instead? how long can i leave it in? i have learned not to leave a calc in alcohol for over a day. it's bad for the screen. thanks in advance.


Hi, D.B.; howdy?

I used alchool vinegar in many situations to remove alkaline residual durty (acid + alkaline(base) = salt + water), tepic temperature to speed the process. I used this technique a few days ago with an HP27 that was actually dead; now it's completely alive, but the keyboard is not working. In fact, it belongs to a contributor in here and I need to send it back to him... I want to just to put the keyboard in working condition before sending it back (first row fails a lot). I removed the IC's (hard job... and worth the effort) and a few surrounding components. Green stuff everywhere, mostly under the IC's (no visible). The HP27 uses the sama HP25's base board, but has only two IC's insterad of the three that comes with the HP25.

It's a bit time consumming but worth the job. If having a working HP25C is the prize, then... go for it!

Best regards.

Luiz C. Vieira (Brazil)


thanks luiz and howdy to you too. i'm ready to start but: what do you mean by alcohol vinigar? a mixture of alcohol and vinigar or is that a direct translation of a way youall describe a type of vinigar? i have some 70% isoprppyl alcohol, some 5% (50 grain) table vinegar but i can get something else if it will work better. i've also got a bottle of cristal brand aguardiente that i got in columbia but i don't think all the exess sugar will do the 25 any good.

and as we say out here in the west: happy trails to you - d


Hi, D.B.;

now I'm in the corner: I know vinegar is mainly obtained from wine, but I have bought Apple vinegar and Alcohol (learning, learning...) vinegar. It's composition is not specified, but it smells as vinegar with alcohol. The only inscription it has is:

Ascetic Leavend of Alcohol (Fermentado Acético de Álcool)

Does it help anyway?

Best regards, my friend.

Luiz C. Vieira - Brazil


luiz; i tried vinigar and it turned blue from all the corrosion. i took that as a good sign. all but three keys feel good now but it dosn't work.

all; when i turn it on it either gives me a decapitated 8 or a decimal point on the right side or three decapitated 8's or dots evenly spaced across the screen. the characters are dim on a fully charged battery and bright with the battery in and the adapter plugged in. any ideas or should i just learn to like the way it looks in the glass case?


Hi, D.B.;

Let me tell you what happened to me a few weeks ago.

I was sent four Woodstocks (not mine) so I would try to repair them. Two of them -HP22 and HP27- showed the same behaviour you mention: random display. The HP22 came back to life after a detailed cleanning procedure. In the HP27 I had to remove the logical set - two IC's - and clean under them. A lot of "cyan" crystals (copper oxide). I used tepid (+) vinegar and I could remove all visible oxide material. Voilá! Both are back to life. The other two are waiting for me for this next week.

There is a possibility of contamination in the display, too. I saw this sort of misfortune in two Spices, because batteries are right under the LED's display. You should inspect to see if the display is O.K. Better yet, you should try the display in another Woodstock, if you have one for testing.

I think there is still some residual between the IC's and the logical board. I must warn you that removing these IC's was not easy: these boards do not have metal-coated holes; instead they have small, thin metal rivets, and the IC's terminals will insist on keeping in contact with them. It's somewhat hard to remove, and in my particular case, there was oxide residual coating inner solder surface. I had to use sharp-edged clips so I could remove the IC's without dammaging the metal rivets. If you are willing to do this, just be carefull and pacient, will yah?

Having a Woodstock back to life worth the job, believe me. And I consider I have been fairly "gifted" (I was gifted a calculator without the need of a commitment to the repairing; I felt myself gifted with the gesture, too), mostly now that my friend's calculators are ready to fly back home.

I hope you have success. Let me know if you need something, O.K?

Best regards and good luck.

Luiz C. Vieira - Brazil


Hi, DB;

I forgot to mention. The same segment on each diaplay is connected in the same copper trail, and each digit has a "common" pole. This allows the display to be "built" in a multiplexed way, say, each digits lights-up at its time, in a sequence.

If a copper trail for one specific segment is not in contact with the driver circuit (bad contact is the major cause), this same segment will not lit in all digits, O.K.? Is that what's happening?


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