The repeater problem has been tracked down. Would never have found it on site. We won’t mention how many hours this has taken.
Solution – the audio input transformer had been burnt out. Originally I thought it had just failed but on replacing the transformer the next one also died. The problem was a blob of solder on the socket for the exciter that was shorting the +12V supply to a bridge connection for the input of the audio. Unfortunately it was intermittent. After putting a third transformer in (supplies getting thin) and resoldering the joint to get rid of the surplus solder there was no longer 12V finding its way onto the audio transformer and burning it out
I have rechecked all levels and adjusted powers on the units. It now requires another trip to Naracoorte to re-install the device.