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HP Forum Archive 16

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Half-Dead HP-25, help needed.
Message #1 Posted by jbssm on 2 Oct 2006, 11:06 a.m.

Hi all,

I have a HP-25 that is not working correctly. It turn on, but the display is full of numbers and everytime I press a key the numbers change but to something completely unpredictable.

Do you think there is a fix for it?

Also, I received this calculator with 2 normal AA batteries (1.5V) instead of the original NiCd (1.2V) batteries. Do you think that was this excess of current that may have damaged the calculator?

Re: Half-Dead HP-25, help needed.
Message #2 Posted by Jeff O. on 2 Oct 2006, 2:04 p.m.,
in response to message #1 by jbssm

The general consensus around here is that using conventional AA (alkaline or zinc-oxide) batteries in woodstock calculators is fine. In fact, some suggest it as normal practice to eliminate the dangers associated with using rechargeable batteries that are recharged in the calculator.
Woodstocks are subject to a variety of problems, some associated with having been plugged into the wall-wart without a good battery pack installed. This has been discussed a few times in the past, for example in this thread. A search of the archives using "woodstock" as a key word should yield further information.

Re: Half-Dead HP-25, help needed.
Message #3 Posted by Randy on 2 Oct 2006, 4:34 p.m.,
in response to message #1 by jbssm

If the unit is clean, without corrosion, that is usually indicative of a damaged ACT chip or possibly a bad rom. Flashing zeros is another symptom. The ACT is the more common failure with ram failures a close second.

They get fried when connected to the charger without a good battery in place as the internal voltage reaches about 8 volts DC without a load instead of the proper 2.5 to 3. That's why it is safer to power with alkalines or batteries charged externally from the unit.

The only source for the the ACT is from another 20 series unit. The 27 is not compatible but anybody willing to cannibalize a 27 to repair a 25 has other issues in play :)

Re: Half-Dead HP-25, help needed.
Message #4 Posted by Hal Bitton on 2 Oct 2006, 10:10 p.m.,
in response to message #1 by jbssm

One suggestion if I may...
Before you pursue the possibility of a bad chip, just be sure you have exhausted all possibility that the problem is not just poor connectivity at one of the battery contacts, or even internally within the battery pack (I'm assuming that since you are using AA alkalines, the welded on strip that connects the cells in a stock battery pack has been done away with, leaving the spring to connect the two cells). I would polish everything with a pencil eraser (the contacts, both ends of the batteries, and the spring inside the battery pack) and try it again.
My 29c will occasionally exhibit symptoms similar to what you describe, and the above mentioned remedy takes care of it. Hopefully that's all that's wrong with your machine. Best regards, Hal

Re: Half-Dead HP-25, help needed.
Message #5 Posted by Klaus on 3 Oct 2006, 3:58 a.m.,
in response to message #4 by Hal Bitton

Have a look in the articles section. I think there is one article describing how to fix some problems without changing the chip.

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