HP 25 and HP25C

[Graan]

Hello

I bought a 25 and a 25C + charger.
The 25 worked (said by the seller) and the 25C was said to have flickering display.
When checking the batteries both calculators had nimh batteries in the battery compartment. The 25 lit up but the comma leds where lit. Else seemed to work.
The 25C had just flickering leds.
I removed the batteries and connected the calculators to a lab power supply (2.6VDC) and both calculators now worked (at least the leds looked normal).

On the 25 I tried to switch to program mode and then the display went out. When checking the current it went up from 140 mA to 200 mA. I switched it off and on again and now it worked again. But after a new try it did not switch on again. Now it does not turn on (at least the dispaly) and the current is 200 mA.

The charger is 10VAC and I suspect connecting it with bad battery connection can damage the calculator?

Questions:

1) Is it ok to use normal batteries (AA Nimh) in the calculators? The caluculator contacts in calculator (for batteries) does not seem to be ideal for normal batteries. I cannot see how you will get a good connection to the batteries.

2) The 25C seemed to work but one thing looked odd. When changing to FIX 4 then turning off the calculator it always starts in FIX 2. Even when changing to SCI notation it always starts with FIX 2.

3) Is it possible to rebuild the HP 25 with the modification by PANAMATIK?

[teenix]

(07-30-2018 08:16 AM)Graan Wrote:  Questions:

2) The 25C seemed to work but one thing looked odd. When changing to FIX 4 then turning off the calculator it always starts in FIX 2. Even when changing to SCI notation it always starts with FIX 2.

The continuous memory does not preserve the display mode setting. It will reset to default after switch off/on.

cheers

Tony

[burkhard]

Quote:The charger is 10VAC and I suspect connecting it with bad battery connection can damage the calculator?

Yes, the charger is evil incarnate and should only be saved for historical purposes. Put a tag on it saying what it is for and warning your heirs never to plug it into the calculator. Charge the batteries off-board.

burkhard

[PANAMATIK]

(07-30-2018 08:16 AM)Graan Wrote:  3) Is it possible to rebuild the HP 25 with the modification by PANAMATIK?

Yes, but not before september. I'm out of office.

The HP-25 new ACT will even keep the display mode after switching off.

Bernhard