No echoes displayed on sounder screen.
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| Advance | YES | |||
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| Speed set to |
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| zero? |
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| NO |
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Configure the navigatorʼs |
| Has the |
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NO | navigatorʼs |
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Aux Port for the 491. See | Aux Port been |
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Section 1 of this manual |
| configured |
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for instructions. |
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| for the |
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| 491? |
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| YES |
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1. Check fuses and circuit |
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breakers. |
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| STEADY | ||
2. Check power to 491 with | OFF |
| Check | ||||
a voltmeter. |
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| GREEN | ||||
the 491's STAT | |||||||
3. Verify that the data cable |
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| indicator |
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between the navigator and |
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the 491 is properly wired |
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and connected. |
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| FLASHING |
| RED |
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| GREEN |
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The 491 and the navigator aren't communicating properly. Check the wiring of the data 
cable between the navigator and the 491.
Change the Advance Speed setting.
491 is communicating with the navigator.
1.Check transducer connector for the proper wiring.
2.If wiring is correct,check transducer impedance with an ohmmeter.
3.If the transducer is open or shorted, replace it
There's a hardware problem with the 491.
Figure 10: Troubleshooting the echo sounder (957/958)
Checking the transducer
To provide the best possible performance with the 491 echo sounder, Northstar recommends the use of an Airmar
491 Echo Sounder Operations Manual | Page 65 |
