hp 25 amnesia



#2

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.


#3

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.

#4

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!

-Katie


#5

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.


#6

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.


#7

ok, I'll inspect under the RAM chip.

thank you.


Possibly Related Threads...
Thread Author Replies Views Last Post
  Strange HP 25 Problem (Repair) Onur Ilkorur 5 1,232 12-06-2013, 05:13 PM
Last Post: Onur Ilkorur
  HP-25 Wayne Selway 1 563 11-22-2013, 12:58 PM
Last Post: Michael de Estrada
  Interesting Base Conversions - Porting a 1975 HP 25 Program to the HP 35S Eddie W. Shore 1 615 10-13-2013, 07:49 PM
Last Post: BruceH
  HP-25/25C Potential Matt Agajanian 14 1,973 07-17-2013, 02:57 AM
Last Post: Matt Agajanian
  Recharging original batteries in HP 45, 65 and 25 Michae Altmann 1 555 03-05-2013, 12:21 AM
Last Post: DavidShenk
  HP-25 keyboard Brad Barton 5 828 02-16-2013, 09:59 PM
Last Post: Brad Barton
  HP 65/25 shout-out in interview with Paul Lutus Egan Ford 3 685 12-21-2012, 11:09 PM
Last Post: Mike Morrow
  New HP-25 Emulator for iPad, iPhone, and iPod Namir 5 890 05-22-2012, 06:22 AM
Last Post: Mike (Stgt)
  Subroutine tactics for the HP-25 Matt Agajanian 3 679 04-19-2012, 05:45 PM
Last Post: Trent Moseley
  HP-25 aj04062 13 1,484 03-30-2012, 03:23 AM
Last Post: Russell Dobson

Forum Jump: