Appologies for the delay getting back to the thread - I thought I
posted at the weekend but it doesnt appear to have uploaded.

Anyway, I removed transistor MJF122 as someone suggests it might be
faulty. With a DVM set to diode function on the ohm scale and the +ve
probe on pin 2 there's no reading on pins 1 & 3. With the -ve probe on
pin 2 pin 1 reads 0.74 & pin 3 reads 0.66. With the -ve probe on pin 1
and the +ve probe on pin 3 there is no reading, and reversed the
reading is 1.03

I popped out the 0.33 ohm resitor and the value is fine, as are the
rest of them and the solder joints too

I have an oscilloscope - can anybody advise where and what signals I
should be looking for please?

Thanks in anticipation.