Possible ground loop?  Check that signal grounds are correctly connected to associated pins and not grounded to "ground".  Also check shield grounds (one side only).  Also check chassis/box grounds are common and not separate ground paths.

 

Grayhawk

 

 

 

So here is a pic of the system info page of my MX20, taken while it was out of the plane on the bench and connected to the SL30(also on the bench).
As can be seen here, both units are functioning normally and it is receiving valid serial date from the SL30 on Port 3. Back in the plane the MX20 receives valid data from the GX60gps, Ryan9900B(TCAD) as well as WX500(LT) BUT NOT the SL30. When installed in the cockpit, Port 3 NAV on the MX20 shows NO and NO and Ports 1, 2, and 4 indicate YES.

Continuing my tale of woe, one would conclude that there is a wiring issue in the plane and there still might be but I can't find it!
The MX20 Port 3 is wired correctly, exactly as it was on the bench. There are no shorts between the SL30 Tx and Gnd pins and the chassis. The same applies to the Rx and Gnd pins on the MX20.

I'm totally stumped so, my current plan is say screw it, turn off Port 3 (which will remove the amber NAV flag from the MX20 display, and get back in the air.....unless one of you avionics wizards can suggest a more elegant solution.

Angier Ames
N4ZQ





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