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 Catalina/Capri 25/250 Sailor's Forums
 General Sailing Forum
 Depth Sound/Motor Issue		  New Topic  Topic Locked
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Don B
Captain

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USA
317 Posts
Initially Posted - 04/30/2009 :  05:32:55  Show Profile
Seems ever since I installed my new Tohatsu, whenever the motor runs, the depth sounder goes haywire and reads 500 plus feet. Normal readings around the Manatee River/Tampa Bay area are 4 to 20 plus feet. Once I shut the motor down, the depth sounder goes back to normal readings.

I have the motor wired directly to the battery and the depth sounder is wired through the electrical panel. Prior to the Tohatsu, my old 2 cycle was not an electric start so the problem didn't show itself at the time.

Appears to be some kind of back feed going on that disrupts the sounder so I was wondering if there is some kind of "isolator" I can install to prevent the back feed.

Has anyone else had this problem or am I just "special".

Thanks for your help.
Don B
86FK/SR #5216 "Mighty M"
Southwest Florida
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HeelinPatrick
Navigator

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USA
102 Posts
Response Posted - 04/30/2009 :  06:29:36  Show Profile
I don't have electric start engine, however, you could check the voltage coming off the motor when running. I'm not real familar with outboard set ups, if they are alternators or generators, but if alternator, and voltage regulator goes bad, it could be sending back high voltage to the battery. Just toss on a volt meter quick to check. Other than that, I can't offer any suggestions. I would think there is such a thing as filter/isolator too.
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Sloop Smitten
Master Marine Consultant

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USA
1181 Posts
Response Posted - 04/30/2009 :  07:15:18  Show Profile
Don,
Over the years I have found an abundant of my electronic problems are caused by faulty ground hook-ups. Make sure your ground connections are not corroded or loose and that the connectors pass muster. Both the engine and the depth sounder connections. And don't forget to check the transducer connections as well. With any luck it will turn out to be a maintenance issue and not a repair.
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aeckhart
Master Marine Consultant

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USA
1709 Posts
Response Posted - 04/30/2009 :  10:20:45  Show Profile  Visit aeckhart's Homepage
If you think that's weird, my depth sounder suddenly started counting down by 10 foot intervals to 100 feet, then to 900 at 100 foot intervals. It did this repeately. Standard Horizon, the manufacturer, suggested that it was in the demo mode and explained how to get it back to normal.

Hope your problem is as easy to fix. Maybe Tohatsu or your depth sounder manufacturer can help as well if the aforementioned suggestions don't help.
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dmpilc
Master Marine Consultant

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USA
4593 Posts
Response Posted - 04/30/2009 :  11:13:09  Show Profile
I've got a new (now 1 yr old) Nissan 9.8 elec start (same as Tohatsu), also wired directly to the battery, as well as my depth sounder. No interference issues. In addition to the suggestions above, be sure the motor is not wired up to the battery backwards.
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Dave5041
Former Mainsheet Editor

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USA
3758 Posts
Response Posted - 04/30/2009 :  12:02:42  Show Profile
I would consider an AC noise component in the DC supply from the motor. Alternators generate AC and a simple circuit converts it to DC; inadequate filtering lets a ripple on top of the DC pass. Your voltmeter may show a continuous, small fluctuation in the motor's output. A failed diode might show a large fluctuation, but that would be followed shortly by a complete system failure. Be sure to check the motor/battery circuit connections, both hot and ground, for poor electrical continuity because some simple filter circuits will pass more ripple with increased resistance.
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Don B
Captain

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USA
317 Posts
Response Posted - 04/30/2009 :  13:51:43  Show Profile
Thanks to everyone for their suggestions. I will have meter in hand when I make my next visit to the boat and will report back my findings.
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Notice: The advice given on this site is based upon individual or quoted experience, yours may differ.
The Officers, Staff and members of this site only provide information based upon the concept that anyone utilizing this information does so at their own risk and holds harmless all contributors to this site.