If I remember correctly there is an amplifier that is just after the SSB filter in the transmit path for SSB, and I think is it on the hidden side of the board.
It can be taken loose and flipped (I use a sheet of paper to isolate the electrical from the chassis). Be careful to make very short test transmissions with low power set. I lost a set of driver transistors while working on one of mine. A scope will make if fairly easy to trace the signal. It may have been a mixer in question, but I have slept since then so I can't be sure.
