I have had some issues with a fish finder getting feedback and interference. Only the one in the front gets noise. There are two times it happens. When i hit the trolling motor and sometimes a more random occurrence.

I expect that the trolling motor is older and just not shielded well (has the transducer clamped to it). The random issue shows a repeating pattern of a short bar of noise every couple of seconds, but doesnt happen all of the time.

The only thing that seems to stand out is the power switch to the live-well pumps goes through resistors (NTE5800) and one of them appears to have overheated in the past (before it gets to the time delay device).

Any suggestions for things to check would be appreciated.

Next time you go out disconnect the electronics battery from your on board charger and see if you are still having issues. More often than not there is a diode in the charger that goes out and allows talk between terminals.

Next option is to wrap your trans cable through a terroid and see if that helps. this would help determine if it is the actual trolling motor proximity.

Either way, you are in for potentially a long goose chase here. Took me 3 months to clear up mine, and it still shows up on occasion, especially in shallow water.

NTE5800 is a diode.. diodes allow current to flow in one direction, basically a switch. So it could be possible that diode is allowing current to back feed. Cathode side, with the band, is negative polarity and anode side is positive. You said it’s burned so that’s where I’d start.

This is one of those things that you can almost write a book about. You may already have things setup like this but first thing is you need to run the graph off of your cranking battery and not a trolling battery. Motorguide says you need to connect the negative battery posts of the crank battery and the first trolling battery (if you have a 24v system, the battery that the trolling motor negative connection is made to) to create a common ground for all of the accessories. I found some copper braid shield that I put over my bow finder power cable and connected that to the negative contact for the finder power. Keep the power cable for the finder as far away from the power for the TM that you can. The toroid core that was mentioned before is also a good option. I saw on one video a guy had drilled a hole in the skeg of his TM and attached a cable to that and run it up to the negative connection for the TM, grounding the case of the TM in the water. I haven't done the grounding the motor case and the toroid yet, but those are next for me.. good luck. its complicated!
BD

Tell us about your fish finder? Brand? New? Older? Noise something new or been going on a while?

There are several options to try to eliminate it.
Does the TM have a fuse in the head? If so check it.
If you move the FF away from the TM does it stop? I moved mine to the right side of the deck and now have none.
Is your FF wired directly to the battery with it's own wire or wired into the boats wiring harness?

A youtube search will show you some other ways to fix it depending on which unit it is. If it is HB then contact them and they have a couple of things you can get to fix it.