Try turning VR11 up. If that does not work it's radio tech time.
First thing I tried.....nothing.
The obvious follow up question would be......Is the AM output OK?
Yes.....its putting out 4 watts on AM....will max out at 5 watts.
That seems low. You should be able to dead key 2-5 watts and swing 10-14 honest watts. SSB peak should be 16-18 quality watts.
How are you measuring SSB power?
Normal speech will only result in about 1/4 or less average power indication out of a full 12 watts power output.
The peaks are there but the metering cannot follow the power changes as you talk.
I know that SSB and AM take different paths to the driver/final.
Sure that 'ExitThirteen' (a member here) prolly knows what to look for . . .