I too had a similar depth sounder/fishfinder. A Seafarer, made in the UK.

The frequency was 150 Khz. Modern sounders seem to be 200 so a new display
will not work on the old transducer.

The problem isn't buying a new unit, the expensive bit is hauling out to
install the new transducer. I bought a new unit and intend to install it
in-hull in an oil bath.

Henry