I have had her back on the bench and initially couldn't find anything wrong. However in real use it become apparent that she was in fact profoundly deaf! Picking up test transmissions from the nearby FT857D or Baofeng outputting into a dummy load was one thing but it wasn't receiving anything else!
From the service manual and schematic I deduced that it could be the initial RF receive amplifier. It is a dual-gate mosfet (3SK76) It proved tricky but I managed to source a replacement on eBay and it was a simple job to replace once I'd extricated the PCB.
I can report it is now working and the video below shows it monitoring the GB3EE repeater in Chesterfield. From the coverage map I shouldn't be able to hear it but I can and reception has been marginal at best using other receivers but it repaired TR9500 doesn't have any problems.
I wonder if the rig has been subjected to a high RF field in the past this could easily have damaged the receiver amplifier and an induced RF into the microphone lead could have damaged the microphone pre-amp. It just seemed strange it having both faults.
Tuesday night is the last 432MHz UKAC contest and hope to use her in anger.