hp 25 amnesia


I've rescued a hp25 from the trashcan where it had been thrown by a colleague (#1509s36887).
After taking apart, cleaning (very beautiful white crystals in battery compartment) with alcohol & plugging a new NiCd inside, it appears that :

- display & kbd in working order

- all basic functions work :arithmetic ops, stack, trig ...

- data : none of the Rx registers memorize anything : RCL returns zero

- instruction : PGM mode doesn't work : the pgm counter increments but any typed instruction displays as "goto 00"

It looks like a failure of some memory to store data/instruction (is there a common place for both) ?

There are 2 chips at PCB top :

- AMI 7523SH 1818-0153

- HP 1820 1382E

The 3 chips at bottom of the PCB are :

- AMI 7523B1 1820-1523

- AMI 7524NE 1820-1564

- AMI 7525CL 1818-0154

I'm completely ignorant : could somebody describe the respective part of each, which one is guilty ? Is there any way to fix it ?
Is there something else I could check (capacitor, transistor ...) ?

Thanks for any help.


The upper two chips are the display drivers. The smaller one also has some ROM code in it.

The large one at the bottom is the ACT chip. It is the CPU and timing generator. The one on the left (0154) is a program ROM. The one on the right (or above the ACT chip on some versions) is the RAM chip. It is the one that ails you. Also some HP25's have two RAM chips.


Take a look in the Articles Forum on this site. There's an write-up about A Common Woodstock Problem that describes the problem that you are expereincing and soutions to it. It's exactly what I've seen on several Woodstock machines and it's fixable!



thanks to both,

Katie, I tried to OFF/ON the calc after several warming hours, without result. I tried also to 20k shorcut the 2 ACT pins but, unfortunately, it doesn't work for me.

Do you know anything else I could try ?
Thank you.


The article describes the things that I've come up with to fix the warm up problem. But since your 25 doesn't seem to work fully even after the warm up period then those tricks probably won't work. In all likelyhood the RAM chip (the one closet to the battery contacts) is seriously dead! Replacing it with one from anohter 25 (22 or other calc with the same chip) is probably your only hope. As a last resort, I usually desolder the chip to check for circuit board problems that might exist underneath it, then solder it back down and hope for the best.


ok, I'll inspect under the RAM chip.

thank you.

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