I have rescued a big bundle of HP 38G calculators

[BruceH]

I replied to your post in the other thread before it was moved into the Classifieds here but my reply seems to have been lost.

Maybe I transgressed some rule but there was at least one important piece of information that should have been retained, namely that the OHP unit (if it is the official HP one) contains a 9v battery. You should open the case and remove that battery before it leaks.

You only need the battery when connecting a 48SX or GX using the "memory card" connector so yours may have been removed previously.