HP25 problem at revival



#6

Hi!

After many (many) years I decided to put my HP25 (bought 1/12/1975) at work again.

I left it because at the time I was told that it was not possible to find new battery pack.

I only now discovered the MoHPC following the advice of someone.

Now I replaced the batteries by new NiMH batteries.

After charging when running the display shows a full line of 0 and nothing modify this.

Any hope to solve the problem?

Thanks


#7

I'm sure others will know better and I don't own one of these fine cals but here is a reasonable guess: After so many (many;) years capacitors tend to go bad. In my experience, this can cause a lot of nasty failures. If no one else will come up with a better idea, replacing all capacitors is worth trying.

Thomas

#8

Most caps in HP handhelds are tantalums... it's rare for them to fail.

The problem is bad ACT chip, it was damaged by the charger being plugged in with a bad battery or no battery in place. The battery is the load for the charging circuit, if the battery is open and presents no load, the voltage inside the calculator rises to 10 volts and damages the integrated circuits.

The only source for the chip is from another 21,22,25,25C,29C or 67. The 27 is not compatible. The ACT is the 22 pin DIP at the bottom of the processor board.


Edited: 19 Feb 2006, 9:53 a.m.


#9

Thanks for the information.

So there is no solution, unless I change the circuit.

Now the problem will be to find it.

Yours,

Alain Delmotte


#10

To find one, setup a saved search on ebay (look for a cheap woodstock - like a 21). The search will email you when it finds one. Bid, win, pay, receive, unpack, warm up the soldering iron...

Of couse, you could just get another 25 or a 25C.

Regarding batteries on woodstocks. I NEVER recharge batts in the machines. Use the external charger unit, or make one, or better yet remove the central plastic bar in the batt pack so it can accept AA rechargeables, and when they're low remove them and recharge outside the calculator.


Possibly Related Threads...
Thread Author Replies Views Last Post
  Official revival of old calcs wildpig 7 434 08-20-2012, 04:11 PM
Last Post: Ingo
  HP25 Programming Failure MikeG 1 170 05-05-2007, 01:54 PM
Last Post: Randy
  Value of HP25? John Polhemus 3 224 02-06-2007, 03:56 PM
Last Post: Thomas Okken
  reparation HP25 french pou 4 308 01-02-2007, 04:41 AM
Last Post: Olivier TREGER
  What's wrong with my HP25? Karen 2 183 11-04-2006, 03:29 PM
Last Post: Randy
  HP25 Memory Grahame Sutherland(Scotland) 15 745 12-09-2005, 05:02 AM
Last Post: Grahame Sutherland(Scotland)
  HP25 without or with polar coordinate bug more valuable ? Bernhard 1 166 10-30-2005, 08:36 PM
Last Post: David Smith
  HP25, HP65, HP67 and HP41 emulators Alvaro Gerardo Suarez 0 124 05-25-2005, 12:05 AM
Last Post: Alvaro Gerardo Suarez
  HP25 PROBLEM JULIO PONCE 4 213 04-24-2005, 01:56 PM
Last Post: Andrés C. Rodríguez (Argentina)
  HP25-C Louis 1 176 02-09-2005, 04:01 PM
Last Post: David Smith

Forum Jump: