@jfrancis49: did you ever find a solution. I am having an oodly similar experience to you. I have a recently purchased 2400-2 and I took the front panel of to fix some connections to the touch buttons. I succeded, but suddenly my FM3 is forever turned on and I cannot switch, not even when touching the pins directly (though holding them seem to have some effect, FM3 is still turned on but there is some signal to the various buttons).
I am really not a tech sawy person so I am crossing my fingers for an easy fix. My alternative is to bring it to a repairshop. This might be needed anyway since it is an old unit and I suspect a myriade of issues once I open it up for cleaning.
Hoping for the best!
/Frederik
