I found that the speed transducer had been bent probably by being under a lifting strap at some point.
I replaced the depth display with a used one and now I get depths displayed but they bear no relation to the true depth and they are squirrelly. I talked to Raymarine
and they say it is the wiring
to the sounder. Unfortunately on a 30 year old cruising boat the wiring
is not immediately accessible. I am considering running new wire and leaving what's there in place but even that will be painful. More after I try this. Any ideas are welcome.