[Yaesu] FT-747 output power wierdness

[Kevin P]

Hi All,

I have recently aquired a FT-747 for a backup/mobile rig and there is a
problem with the output.  It seems that it oscillates on SSB with no audio
or CW with the power all the way down.  I am in the process of moving and
have most of my test equipment packed away but from what I can tell the PA
unit still puts out power with no input at all (unplugged the mini coax).
The power output also varies widely, 140 watts on 20m to 25watts on 160 and
10m.  When the radio is keyed with no mic on ssb the fan will come on in a
couple minutes (gets hot fast).  The two 2sc3133 drivers are getting very
hot so I suspect one of them is bad.  Also if I gound the input to the PA
the oscillation disappears and the final idle current looks in spec with the
input grounded, it goes to an amp or so when it oscillates).  The radio
looks untouched and unmodified in any way, any suggestions/experience with
this?

Thanks,
Kevin
K9KJP