Dear Menachem fine to hear from you
I thought the same, and pulled out U500 trigger, yesterday.
Completely clean, AMP socket gold pins perfect.
I used static precautions and 99% isopropyl alcohol, and a q tip to wipe the IC contacts and sockets pins.
No change in the symptoms after reassembly
I suspect that there may be missing or wrong cables or connectors to the options boards.
I shall start a new topic on what I discover.
Best Regards
Jon
Jean-Paul