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Old 597 DI - Head or Transducer Problem?

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skipt:
Love my 597 but noticed recently that sonar isn't working.  I only get a very small trace near the surface, even after resetting to factory defaults.

DI works most of the time, although it doesn't seem as sensitive as it used to be, and every so often fails to work at all.  Power cycle or factory reset usually fixes that.

I am willing to go for a new transducer or head, but would like to make the best possible guess as to which one is more likely the problem.

I am an engineer so apologies if the following is too _nal.

I remember when the unit was much newer years ago, you could really tell things were working when the transducer was powered and out of the water.  I could hear clicks and pick them up on a nearby AM radio.  Putting a fingertip on the transducer actually caused a little pain.  None of this happens anymore, so I suspect either the transducer and/or the driver electronics in the head have degraded.

I disconnected the transducer from the head and upon power up the head correctly reported that the transducer was not connected, so there is some connectivity there.  The temp sensor is working fine too, I can raise the temp with my fingertip.

I'm thinking of either tapping into the transducer cabling and putting a scope on the leads to see the driver pulses and signal responses, or, opening the head to inspect the driver circuitry.  I would expect inside the head to find a large capacitor and maybe one or two power mosfets in the driver circuitry, and if so, might remove those components and check for degradation/failures.  I'm also wondering if the head has an internal coin battery for NV memory retention.  Those batteries don't last forever.  Does anyone know in advance what I will find?

Another alternative would be to put the head on the bench and use some resistors to simulate the transducer elements.  I have the pinout for the transducer cable and would use a scope to look at the driver pulses.  Does anyone know a good resistance to use and what size driver pulses I should expect?

NOS transducers are available but I'm wondering if they can degrade during years of sitting on the shelf.  I imagine internally the transducer has the elements encased in epoxy which would seem to be a pretty stable environment.  Opinions or facts on this welcome.

rnvinc:
Do you have access to another compatible transducer for troubleshooting  ... ??

Rickie

skipt:
No I don't.  I might buy one but first trying to get smarter, like I said, it might be the head.

ezfishn:
Rickie is far smarter than I on these units but I believe the DI is dependent on the 2D working.  So if your DI is working then the 2D should also.  Also, true the transducers can age over time and become weaker.  Where is your DI transducer mounted?  Are you getting a valid depth reading?  I'm fairly certan there aren't any internal batteries in the units. 

skipt:
The engineer in me is suspicious that the DI depends completely on the sonar working properly.  Here's why:  the active element in the transducer is most likely a piezo ceramic like barium titanite, and such an element will have a resonant frequency that depends on the geometry (physical shape and dimensions) of the element.  The fact that DI and sonar use different frequencies suggest that there is a separate element for each function, each with its own physical size and resonant frequency.  Also I'll note that my transducer (710226-1 XNT 9 DI T) has separate signal wires for the DI signal and the sonar signal.  This further indicates that there are separate transducer elements for DI and sonar.  And if there are in fact two different elements in the transducer, it would be possible for one element to degrade at a different rate than the other. 

Regarding depth determination:  if there are in fact separate transducer elements for DI and sonar, both the DI and the sonar would be capable of determining depth.  Depth is determinized by the arrival time of the return pulse and the (known/fairly constant) speed of sound at the given frequency in (fresh or salt) water.  The imaging however (DI or sonar)  is determined by the strength (not the arrival time) of the return pulse, which depends on the density of the reflecting structure AND the receive sensitivity of the transducer element(s) and the sensitivity of the receive electronics in the head.  I've already stated there may be separate elements for DI and sonar, and there also may be separate receive electronics in the head for each function.  So there are lots of different ways for the 597 to be designed and lots of different ways for the performance to be degraded.  Unless someone with some inside knowledge steps up, I'll be turning over rocks for a while longer.

If anyone has any dead transducers laying around I'd be happy to cut them open (I do stuff like this all the time) and we could all learn more about transducer internals and their possible failure modes.

My transducer is mounted on a trolling motor, I usually only use the 597 when trolling.  I am getting valid depth readings and decent images using DI, although the DI images don't seem as crisp as I recall when the 597 was new.  Next time out I'll check to see if I am getting valid depth readings when using sonar only. I still haven't opened up the head yet, but that day may be coming.  When I do that I might be able to determine if there is separate circuitry for DI versus sonar, and if there is an internal battery to retain user setting across power cycles.

UPDATE:  WOW, I found this video showing showing a 597 transducer leaking some goo:  (about 50 seconds into the video):

https://www.youtube.com/watch?v=cOctMvqZaN0&ab_channel=DinsmoreOutdoors

I know that the transducer elements need to be acoustically coupled to the transducer housing but I thought they were doing it with epoxy, so this goo is a surprise.  And then, upon close inspection of my transducer, the pointy end seems to have a hole that seems to be sealed with some black silicone-like RTV stuff.  I bet they inject the goo and then seal up the hole.  More stuff to ponder I guess.

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