still amnesic HP-25 : a last hope?



#2

I posted a message a few months ago after I bought a HP-25, beacause it had the "amnesy symptome" (registers always 0, program full of GOTO 00). Since then, I have followed the repair tips and soldered a 20k resistor where needed (and also the jumper), but it still does not work. But another problem on my 25 is corroded circuits caused by a battery leak. So maybe there is a bad trace somewhere that could be fixed by bypassing it with a wire?

Look at this photo of my board. You can see the corroded trace on the right; there is also corrosion under the RAM chip. Do you suspect any of the corroded circuits to be a possible cause of my problems?

A complementary question: what is the function of the chip on the left and the two at the top? (I guess the top ones are for the LEDs?)


#3

Corrosion is a major problem - esp. from the nicads. Since the "blue stuff" is hygroscopic, it will shorten PCB traces and ICs; applying power to the calc will most certainly damage something, as the chips are extremely sensitive. (Don't touch unless you are ESD safe!) I would call this a lost case, it's probably the best thing to sell this one off as "partly working" and buy a new one on ebay...

#4

Corrosion under the chips could be the problem (but it is most likely a bad RAM chip). If you have an ultrasonic cleaner, try standing the bottom end up in vinegar (imerse up to the battery countacts) and running the cleaner. The rinse the board very well, and run it through three more cycles of clean water (change each time). Shake dry (better, blow dry with canned air) then let the thing dry in a warm place overnight.

#5

Quote:
I posted a message a few months ago after I bought a HP-25, beacause it had the "amnesy symptome" or, 'symptoms of amnesia'?/ (registers always 0, program full of GOTO 00).

The two other respondents seem to understand your true question. I would have to assume that the neither storage registers nor the program space will even accept input. The HP-25, I believe, will clear the contents of the storage registers and program space upon shutoff. One needs an HP-25C with Continuous Memory in order to have those preserved while the calculator is off.

-- KS


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