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Need help troubleshooting a problem - Is the Source the VPX or Garmin Nav Comm?

cccjbr6

Well Known Member
Has anyone encountered this problem before or have any ideas? I have been running a 2 screen Garmin G3X suite with a VPX Pro for four trouble free years, until now. On a trip to Palm Beach last week the GTR-20 remote nav comm (COM 2) stopped transmitting, but continued to receive just fine. Cycling the power changed nothing. The VPX page continues to show a green check by the GTR-20. The message screen on the MFD showed two alerts: "COM radio 2 hardware fault" and "COM Radio 2 power supply fault". The flip flop window for COM 2 on the PFD for COM 2 says "TX Hardware Fault." I did not think to check the current draw listed for the GTR-20 on the VPX page while I tried to transmit.

My initial thought was that the power supply had failed partially on the GTR-20. A call to Garmin revealed that while that could be the problem, they had a couple nav comms that were sent in for repairs recently (neither a GTR-20) for the identical reason (received fine but would not transmit) that were powered through a VPX. The power supplies tested good however and teh radios were returned to their owners. Garmin never heard what the problem turned out to be on either one. They suggested that before I return the GTR-20 for repairs I have the current the VPX is supplying to it measured while transmitting to make sure it is at least 7.5 amps.

I have a call in to Chad Jensen at Vertical Power but he is on vacation currently. Before I seek out an avionics tech to measure the current draw, I thought I would poll the group. Has anyone encountered this failure mode before or have any insights/suggestions?
 
you probably should rule out a couple of the obvious issues before heading down repairs with either units.

  1. What does the VPX show as current draw? idle? Transmitting?
  2. Measure the voltage on each of the power pins on the tray of the radio.
  3. Validate that the VPX is still configured appropriately.
  4. Validate that when you turn off power to that pin in the VPX configuration tool, that is does indeed disable voltage going to the appropriate pin.
 
I know that a loose connection on a circuit breaker will yield the exact conditions you list (receives find but does not transmit).

Disconnect the radio from the VPX and temporarily connect it to a battery or power supply via a 10 amp fuse or breaker and see if it works.

Carl
(Not a VPX fan)
 
Hello Chris,

In addition to verifying that sufficient power is getting to the GTR 20 on pin 1, you will also want to make sure it has a really good ground on pin 20.

Most of the wiring in your system is 22 AWG, but we specifically call out 20 AWG wire for both power and ground to feed that big 10W transmitter on the GTR 20/200.

The voltage drop will be excessive when you key the radio if the wiring and connections are not up to the task.

Thanks,
Steve
 
Hello Chris,

In addition to verifying that sufficient power is getting to the GTR 20 on pin 1, you will also want to make sure it has a really good ground on pin 20.

Most of the wiring in your system is 22 AWG, but we specifically call out 20 AWG wire for both power and ground to feed that big 10W transmitter on the GTR 20/200.

The voltage drop will be excessive when you key the radio if the wiring and connections are not up to the task.

Thanks,
Steve
Steve,
The GTR-20 had been working flawlessly for four years when then the problem arose suddenly in flight in smooth air. Would that suggest wire size issue is not the issue and perhaps point to something like a sudden change in the ground quality?
 
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