[Icom] Icom 706mk11G no SSB tx

[Paul R]

Hello Icom Gurus,

I have just purchased a second hand Icom 706MK11G. The radio looks to be in 
immaculate condition but upon hooking it up it will not TX on SSB.

This is what I have checked out so far:

I have reset the cpu to factory default.
I have made sure that the mic gain is set at around 6 and that power is hi
I have tried both the front and rear mic sockets.
I am txing in Amateur bands
When I press the mic the tx light goes on but no audio is picked up by the 
radio and hence no power output shown
The radio does tx normally on fm and rtty
Have made sure the mic is not locked (not sure if this affects tx).
Same problem on all bands (including 2 and 70cm).

I don't have a spare 706 mic to test but can probably get my hands on one!!

Can any one suggest what I may be doing wrong before I box it up and shoot 
it off to Icom repair.

Thanks

Paul R