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Garmin Unsupported Transducer Message
The message "Unsupported Transducer" is often caused by insufficient power to the chartplotter or sonar module. Here are a couple of things to try before delving into the chartplotter or sonar module's power.
First, verify that the transducer is compatible with the chartplotter. Garmin's transducer page can be used to determine compatibility by filter tools on the webpage's left side.
NOTE: The base STRIKER™ 4 fishfinder and non-cv STRIKER™ Plus fishfinders can use the GT20-TM 4-pin transducer even though it is not listed on the transducer selection list. If the GT20-TM is connected to a STRIKER 4 or non-CV STRIKER a unsupported transducer message will appear. Selecting Dual Beam 200/77khz removes this error message and gives functioning traditional sonar.
Transducer Connections
Inspect the connections from the transducer to the chartplotter or sonar module. If there is an adapter cable on the transducer, remove it and check for corrosion, bent pins, and broken or loose contacts. If there is visible damage on the adapter, replace the cable. Likewise, if there is an extension cable between the transducer and the device, inspect the connections at both ends of the extension. If visible damage is found, replace the extension cable. Ensure that when the transducer connection is plugged back into the chartplotter or the sonar module, it is seated well. Use dielectric grease to protect the connections.
Software Update
Make sure that the device software is up to date. Garmin releases software periodically that has feature enhancements and improvements to the operating software.
If the above steps have not resolved the issue, the chartplotter / sonar device power will need to be looked at. Follow the troubleshooting steps found in Garmin Marine Device Not Powering On. Specifically focusing on checking the Power Cable