HP 25 schematics? IC pinouts?



#3

Hello,

I'm trying to fix a broken HP25. When I turn it on, the display shows all 0's.

It has some apparently minor damage PCB damage from a leak, fortunately not reaching the ICs at least.

Does anyone have a schematic or at least some of the IC pinouts so that I can check if clock frequencies are where they should be, etc?

Thanks in advance,


Borja.


#4

I wouldn't be too optimistic it can be repaired... I've seen a lot of them in that state and 99% of the time it is a chip failure.

You should have a ~700khz semi-sine wave on pins 13 and 14 of the ACT IC, the 22 pin package. If you don't the chip is dead.

If the clock is running, look for a +5/-12 175khz system clock on pins 16 and 17.

It might be a bad rom (1818-0154) but I think you'll find the ACT is the problem. The only source will be from another 25. Some others from the 20 series may work but it's not a sure thing.


Possibly Related Threads...
Thread Author Replies Views Last Post
  Strange HP 25 Problem (Repair) Onur Ilkorur 5 913 12-06-2013, 05:13 PM
Last Post: Onur Ilkorur
  HP-25 Wayne Selway 1 400 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 1 437 10-13-2013, 07:49 PM
Last Post: BruceH
  HP-25/25C Potential Matt Agajanian 14 1,495 07-17-2013, 02:57 AM
Last Post: Matt Agajanian
  Recharging original batteries in HP 45, 65 and 25 Michae Altmann 1 399 03-05-2013, 12:21 AM
Last Post: DavidShenk
  HP-25 keyboard Brad Barton 5 592 02-16-2013, 09:59 PM
Last Post: Brad Barton
  HP 65/25 shout-out in interview with Paul Lutus Egan Ford 3 462 12-21-2012, 11:09 PM
Last Post: Mike Morrow
  New HP-25 Emulator for iPad, iPhone, and iPod Namir 5 613 05-22-2012, 06:22 AM
Last Post: Mike (Stgt)
  OT: Cal-Tex or "How to remove the lid of an old IC"? Joerg Woerner 7 663 05-07-2012, 08:01 AM
Last Post: robert rozee
  Subroutine tactics for the HP-25 Matt Agajanian 3 470 04-19-2012, 05:45 PM
Last Post: Trent Moseley

Forum Jump: