failed sitex-honda depth sounder circuit diagnosis

[sdowney717]

I have this nice older depth sounder that the transducer cord failed and so the output was either open, so no circuit or shorted to the ground.
I have the manual with the schematic and know that these things send out a sound pulse and then hear it back again. It is not sending out the sound pulse.

So if someone could look at the schematic perhaps they could tell me which component would fail if the transducer suffered an open circuit like no transducer plugged in or a short. Transister? Diode? IC?
I recall the ground cord sheath failed so likely the sounder ran open circuit on the transducer.
I think the bottom left is the sound generator? And top left is the listener?

the transducer plug is the round one on the left with 3 terminals

[Frosty]

They are less than a 100 dollar new.

[CDK]

Bottom left is the pulse generator. To check its function you need an oscilloscope, without that you are groping in the dark.
It is highly unlikely that the circuit died from a missing transducer, but a short might kill Q203/204.

[sdowney717]

I tend to agree with transistors going bad.
there showing Q203 and Q204 being the same, a 2SC2655
Q201 and Q202 as 2SC1815. looking at schematic picture, the emmiter collector arrows are mirrored, so dont see how they could be the same? but looking at the board, they are rotated so it is so. I have the parts number list for each component.

I look at the schematic and see an output transformer T201 with 2 diodes, parts are IS1588.
transistor output runs threw the coil
Would the transformer isolate the Q output to protect from short?

First I need to test it with another transducer.
I have 3 bronze in hull transducers. An Apelco, this sitex, and another left over from previous owner.
That one has a different rusted plug end which is like a radio antenna screw plug only much smaller.
I can cut that off and splice into the plug of the sitex for a test.

Do transducers have any ohm test range?
If still not working, I think I will unsolder and replace some parts.

[CDK]

All 4 have their emitters to ground, so they're NPN; the 1th pair probably .1A, the 2nd pair .8 or 1A peak current.
The transformer is there because with 12V supply you cannot obtain the 100-200V swing to excite the transducer. That is a piezo-crystal. infinite resistance for DC. For testing any type will do.

[sdowney717]

starting to wonder if it is the transducer.
I plugged in an CUDA 128, hooked up the transducer wire and it stays in demo mode. According to the cuda manual, that means the transducer is not working.

The sitex when hooked up displays nonsense number of around 33.
I do have one known working transducer on the apelco xcd 350 with a 7 pin circular configuration. I started another thread about the unknown pinout.

I decided to buy a garmin transducer off ebay which I checked on the airmar site and know the config of the wiring It is a 6 pin plug 6F-Airmar

http://cgi.ebay.com/ebaymotors/ws/eB...K%3AMEWNX%3AIT

this transducer works with all these here
https://www.gps4us.com/GARMIN-Thru-H....html#products

airmar webcache of transducer pinout for garmin part number 31-665-2-01
http://webcache.googleusercontent.co...www.google.com
picture of pinout
http://airmartechnology.com/uploads/...ams/91_231.pdf