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Dave's RV-7A Builder's Log
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Date: 1-1-2017
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Number of Hours: 3.00
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Manual Reference:
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Brief Description: Radio harness modification
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My research into why my G3X system would only recognize GTR 20 #1 led me to the schematic and installation manual where it clearly showed that the second GTR 20 must have two pins jumpered together to identify it as the second radio in the system. I also believed that I had a CAN bus issue due to the fact that there was no termination point at the end of the CAN backbone. If none of this makes any sense, don’t worry, I didn’t completely understand it either…but I do now. CAN is an acronym for “Controller Area Network” and it allows various components on the network to share data with each other. In the case of the G3X Touch, the CAN bus is what allows the display units to tune the radios & transponder, share GPS data, provide redundancy, etc. One primary factor of a CAN bus is that you must have two termination points to tell the system where the bus begins and ends. In my system, the boys at Steinair used the MFD as one termination point…but never terminated the bundle anywhere else.
With that, I opened the GTR 20 #2 connector and installed a jumper between pins 8 & 27 to identify that radio as #2, and also installed a jumper between pins 25 & 26 to terminate the CAN bus at the #2 radio. Put everything back together and power it up…after a bit of internal software loading the #2 radio appeared! Not to be picky, but you would have thought that with all of the fine work done by Steinair, they would have at least gotten that part on the schematic. It’s there now.
My last task was to see if I could get a GPS signal to the GTN 625, so I aired up the tires, pulled the airplane out on the ramp and waited…and…no signal. After pulling it back in and closing the door, I had a funny feeling that it had to do with installer error on the TNC connectors. A quick check proved me right…that problem can be solved with a little time and money.
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Out for a little fresh air...
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