If your experiencing distortion and a fludder while receiving single sideband or CW, more than likely the RF trimmer capacitors on the PLL board will neeed to be replaced.

From my Inventory. I put together this Trimmer Capacitor KIt for the Icom IC-R71A, Icom IC-745 and the IC-751. The same kit was used in my electronics lab to repair over a hundred Icom models. The values were selected to meet the tolerance and specifications that are specified in Icom's Service Bulletines.

It requires removing the PLL board and the top and bottom shields. You will need  heavy duty soldering and de-soldering tools. and a pencil type soldering iron. 

The kit includes 6 trimmer capacitors for the PLL board and one for the main board. It also includes instructions.

By right clickng on the adjustment photos , you can "save image as" a jpg file. When your ready to change the trimmer capcitors, use the adjustment proceedure for your Icom model.