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[Fishmael]

I have a problem with my Fishmark 480 that is up front.  As I am going along, it will be showing the depth, then all the sudden, the depth will start going crazy.  It shows that it is getting deeper, usually to about 180-200 feet and then starts flashing for a bit before it gets a new reading and then will show the proper depth of 8 ft again.  The problem is that it doesn't just happen every once in a while.  It actually happens so much that I cannot rely on the graph to work when I need it to.  Any thoughts or suggestions as to what might be causing this problem? 

[Revtro]

3 possibilities that I can think of.  You could be getting interference from your console unit if you have one.  I had a similar problem.  I changed one of the units to a different frequency and the problem went away.

I also had a problem with my trolling motor causing interference.  I went to digital Motorguide and that problem went away also.

The only other thing I can think of is to turn the sensitivity down. 

If none of those fixes it, you might need a new head unit.  They do go bad, but Lowrance is pretty good about helping you out with replacements.  (Lowrance and Eagle are the same company)

Pose this question to Slipkey in the electronics board.  He's really good at this stuff. 

[Slipkey]

Fishmael,
Bigger than the depth reading itself, how clear is the image on your screen?   I had a bad transducer I fought for several years that, once switched out, gave me perfect readings and reception.

Also, is there a graph on the boat console and does the problem go away when the unit on the console is switched off?

[Fishmael]

You know, I've never had the front one on when the console graph wasn't on as well.  The image is pretty clear, but it never stays set long enough to really guage what I am looking at.  There is some clutter I guess though.  I wish I could take it out and try it to see, but I just had it winterized!!    Is there a way of checking now?  Or am I kinda out of luck until spring?  Should I try a new transducer?  I believe the graph is only 2-3 years old.  However, I bought the boat last spring and cannot say for sure. 

[Slipkey]

It's usually next to impossible to test it on a trailer, especially on a shallow bass boat hull - not to mention inteference from the trailer crossbars and frame.   

You could launch the boat and just use the trolling motor to test it out.   If you have two identical or similar models, it's common to get interference between the two.   You can sometimes adjust the ping speed in the unit sonar settings to solve this problem or simply stop the chart on the console unit when you go up to the bow. 

A new transducer is expensive so a new one should be a last resort.   Most transducers degrade over time starting with loss of signal at deeper depths.   There are many factors that can speed this up so it could very well be that you need a new one.   If you can find a friend that has the same transducer and is willing to let your un-rig/rerig theirs, you could "try before you buy."   

The model transducer the 480 takes, however, is the PD-WSU or PDT-WSU (the latter has the built-in temp sensor) and they are discontinued from most suppliers (including my own) so you might be able to pick one up on clearance or a closeout on eBay.