L755 Fishfinder and correct transducer.

Hello Chuck and all.

This is an old story I want to resolve when we haul out next year.

I was originally sold:
Transducer Bronze
Tag on cable reads:
06-1197 M78923
50-200 Khz
RC 1822/31-114-1-01
With a manual for a B66V
L750 Fishfinder.

I have been told that the above was wrong because it was
Wrong Material for Steel Hull
Wrong manual
Wrong txd for L750

It never worked but I had to leave the country for weather window to cross South Atlantic.

The L750 then died, totally, dead.

I purchased an L755 Hsb Plus to replace it while visiting USA and left for Spain.

It also never worked when I installed it :(

I have the opportunity to haul the boat and correct this, now, its either the L755 or the Tdx, or incompatibility.

Can I peep at the service manual for the L755 to show me how to test if it is OK?
I'd hate to buy a new TXD and its the Fishfinder thats faulty.

IF OK> Please tell me what transducer to buy? (B66029?)No ref on Airmar site.
IF NOT OK> Please tell me what fishfinder to buy to use my existing TXD?

I am retired on small SS so take it easy on me please.

Kind Regards!