Mark,
thanks for the quick response! Autocom just identify the system as CR4, which got me no further. My notes show a four pin AMM, pin 1 (black/white)nbv, pin 2 (yellow/brown) earth, pin 3 (grey/yellow)gave a low speed digital output and pin 4 (green/yellow)gave a 2.4 kHz plus output. Unfortunately I didn't save the traces. Does that help identify the system? It looks as though I might have to add ESI to my armoury,
Peter