I doubt it's applicable to your situation but twice in the past few
years I've had problems caused by the "fingers" in the RJ connectors
on the back of the LNAV that connect the meter and the GPS-NAV. They
get tarnished or lose their spring or some combination. Doug Jacobs
mentioned it to me so although it may not be widespread, it's
apparently not confined just to my instrument. The easy fix is to take
the cover of the LNAV and gently (with great care) push the contacts
on those connectors from the inside of the instrument to add a little
more tension.

Chip Bearden
ASW 24 "JB"
USA