Intermittent fault Raymarine i40 Bidata display

[Peter McNamara]

I have recently replaced the display unit for my ageing Raymarine ST40 log and depth unit with an i40 BiData display, keeping the existing transducers and wiring in my yacht.
The new i40 unit intermittently displays depth data which either flashes on and off or blanks out entirely to a series of dashes at low depths eg. Below 4 meters.
Above that depth everything appears to function well.
I have double checked the connections, installed new terminal connectors, repeated the firmware setup and re-tested the old transducer function by replacing the old ST40 unit which still works.
Can anyone out there please shed any light on what is happening?

Many thanks

Peter Mc