HP-97 decimal point with ghost segment d

[AndiGer]

I have here an HP-97 that always shows the decimal point with the digit d dim lit no matter where the decimal point is shown. No other strange behaviour.

I put another working main board into the rest of the calculator and all works ok but when I drop the main board into another known good HP-97 the ghost digits switches together with the main board to the other calculator.

It is the newer layout of the main board not contained in the service manual I once posted here.

I replaced C1 (2.2µF tantal capacitor) but that didn't change anything.

Any ideas?