hp65 hardware issue

[teenix]

If it is a key contact issue, then that usually causes missed or doubling of the key function.

If it runs ok other than those keys, then the system itself seems to be working.

There are other keys in common with 8, 5 and 2.
C, LBL, STO, CHS, and the Decimal Point. Do these work ok?

You can check for corrosion around the large Hybrid IC near pin 26, which is the common pin for those keys, (see attached) which may cause partial shorts with adjacent pins upsetting the key decoding. Maybe spray some of the cleaner under and around this part - let it dry thoroughly before using the board.

Worst case, the key decoding in the CTC IC is not working properly or other IC's like a ROM, which unfortunately are all in the large hybrid IC and unserviceable.

cheers

Tony