frank1492 wrote in
:

More than you wanted to know, but that's it. I'm suspicious that
the depth transducer itself is faulty, but what are your thoughts? And
if you think it is, how easy to replace?


Piezo crystals always have a kind of static DC voltage across them. It's
what makes the barbecue grill lighter arc when the hammer hits the piezo
crystal when you push the button.

This voltage can be measured with a digital voltmeter where that RCA
connector goes into the back of the sonar unit. Unplug the connector and
leave it hanging for a couple of hours, then measure the DC voltage with
your digital voltmeter. Little boat transducers don't produce much
voltage, but if it reads anything, the transducer is connected through
the wires which are not shorted or soaked in seawater, which will short
out the voltage. (If you just set a big transducer from one of our
submarine sonar arrays on a pallet unshorted, the voltage that
accumulates from sound noises hitting the big crystal is enough to put
you ON YOUR KNEES! Been there, felt that...(c

If you measure no voltage at all from the open crystal, switch to
resistance (ohms) and see what it reads. It should read infinity
(overrange on digital multimeters), not some low resistance or zero.

If it's not shorted or leaking down through some resistance but has no DC
voltage to measure from the noises under the hull, I'd probably say it's
DOOMED and to replace it, which usually means going into the yard as it
comes out the bottom.....sorry.

Another good checkout is to find someone else with your same sonar model!
Take the sonar head over and plug it into his sonar transducer. If it
still reads crap, the head is bad, not the transducer, obviously. If you
can borrow a loose head, drop it over the side so it's submerged then
plug it into your sonar unit. Same thing if it doesn't work...bad sonar,
not transducer.