As a follow-up, I removed the relay from the RF Board and then just bridged the Cal & RF input pads using a piece of wire. The unit passes its self-tests with the wire bridging AT1 (pad 2) and the 50MHz Cal pad (pad 8) , it also shows the RF input very close to what the signal generator is putting out (only 50Mhz as I'm using a piece of wire held in my hand).
The one strange thing was that the control voltages for U38 were +/- 9V rather than +5v & 0V, I'm not sure if that is indicative of problem further up the chain that could have been causing the relay to fault.
TonyG
