HP-25 Isopropylalkohol

[Tom Flatterhand]

(04-06-2022 06:32 PM)Frido Bohn Wrote:  Just as a reminder in the case that you don't know that the Achilles tendon of the HP25 is the use of external power supply without batteries being in place. The use of power through the battery contacts is fine but beware of applying power on the contacts at the bottom of the chassis without batteries that serve as a kind of overvoltage/overcurrent buffer.

Thanks for the tip! When I bought an HP-29C on an auction platform the other day, the seller also pointed this out to me. That's why I used a lab power supply, set the voltage to 2.5 volts and the current to a maximum of 200 mA.

It is quite possible that I have destroyed a Privileg PR 56 D-NC, which I bought a few years ago, in this way. Also then I had not inserted batteries (3*AA) and connected the power supply. But only through the references to this weakness with the HP calculators I have now recognized the connection.