Gareth, I am no expert on the 701, but I do own a 551D and a 251A, which I believe use a similar tuning scheme. First, you should go to the Icom website and look for 'commom problems' with this radio Second, get a Service Manual (I have been very happy with W7FG's reproductions) I would suspect there is a problem with the chopper wheel diodes...... ron N4UE