Garmin SL40 on permanent transmit - Help

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My aircraft is fitted with a Garmin SL40 transceiver which now transmitts as soon as it is turned on!!!

I have disconnected the PTTs and inspected the PTTS wires for damage or wear, nothing. This leads me to believe it could be an internal problem.

Does anyone know much about this transceiver, had a similar problem or have a wiring diagram for the SL40?

Thanks in advance,

Gary