Well I have been asked to look into this.
the master section MONO button is always on (not only the bulb but the function itself) and it only changes when External to monitor are pressed in.
I am offsite and currently looking at the 82154 card which controls the logic of that part of the centre section.
my take is that T11, T21, T23, T24 might not be ok.
any input?
Mattia.