Mission Planner Telemetry Connection Issue - 'The connection port is closed' / 'Failed to enter command mode' Error

Hello everyone,

I am having trouble connecting my Radiolink Pixhawk 2.4.8 flight controller (running ArduPlane firmware) to Mission Planner using a Holybro 3DR 500 mW 915 Mhz Radio Telemetry Set v3.

My Hardware:

Flight Controller: Radiolink Pixhawk 2.4.8 (ArduPlane V4.5.7)
Telemetry Set: Holybro 3DR 500 mW 915 Mhz Radio Telemetry Set v3 (Ground and Air Modules)
Ground Station Software: Mission Planner (Version: 1.3.82)
Operating System: Windows (Version: Windows 10)
Ground Module USB Chip: FTDI (Seems to be FT232TL based on Device Manager)

Basic Problem: I cannot establish a wireless telemetry connection to the Pixhawk from Mission Planner.

Telemetry Radio LED Status (When trying to connect wirelessly):

  • Ground Module (Connected to PC via USB): Green LED is blinking. (It seems to be blinking slowly). Red LED is off or not noticeably active. (If your red LED sometimes blinks rapidly, you can add: “Sometimes the red LED blinks rapidly next to the green one.”)
  • Air Module (Connected to Pixhawk): Green LED is blinking. Red LED is blinking rapidly.

This LED status indicates that the two telemetry radio modules are not establishing a wireless link between each other.

Attempted Step to Fix (But Failed): I understand that to fix the radio link (make the green LEDs solid), I need to match the settings (especially Net ID) on both radios using the SiK Radio tab in Mission Planner (Initial Setup → Optional Hardware → SiK Radio).

Errors Encountered When Trying to Access SiK Radio Settings (Main Obstacle): When I connect the ground telemetry module to my PC via USB and try to access the SiK Radio tab (e.g., by clicking “Load Settings”), I consistently get the following errors:

  1. Error 1: “Error during read System.InvalidOperationException: Bağlantı noktası kapalı.(


    )

  2. Error 2 (Sometimes get this one instead):Failed to enter command mode. Try power-cycling modem.(


    )

These errors prevent me from accessing the radio settings in the SiK Radio tab, so I cannot check or match the Net ID or other parameters.

Troubleshooting Steps Attempted So Far (Without Success):

  • Tried different USB cables for the ground module.
  • Tried different USB ports on my computer for the ground module.
  • Verified the correct COM port and Baud Rate (57600) are selected in Mission Planner connection settings.
  • Verified the port settings in Windows Device Manager (57600, 8, None, 1, None) - they seem correct. (You can add: “Included a screenshot of Device Manager port settings.”)
  • Downloaded and installed the latest FTDI VCP drivers. (You can add: “I used the FTDI UNIN tool for a complete clean removal before reinstalling.”)
  • Restarted the computer multiple times after driver installation.
  • Followed advice to configure Pixhawk’s TELEM2 port for telemetry and physically moved the air module cable from TELEM1 to TELEM2. (The radios still do not link after this).
  • Physically cleaned the USB ports and telemetry connectors (removed dust).
  • Tried the suggested fix for Mission Planner freeze (“Connect reset” toggle in Planner settings).
  • Tried power-cycling the telemetry modules by unplugging/replugging USB.
  • Checked the Holybro V3 modules for a physical reset/boot button (I couldn’t find one on my modules, though some documentation mentions one).

Specific Questions / Request for Help:

  1. The main problem is the radios not linking (blinking green). I understand this is likely due to mismatched settings (Net ID).
  2. However, I am blocked from fixing the radio settings by the “Bağlantı noktası kapalı” and “Failed to enter command mode” errors when trying to access the SiK Radio tab.
  3. What are the most likely causes for these specific errors, and are there any other troubleshooting steps I can take on my current computer setup to resolve the COM port access issue?
  4. If these errors cannot be fixed on my current PC, I understand testing the ground module on a different computer is recommended to determine if the module is faulty.

Any help or suggestions to overcome the “Bağlantı noktası kapalı” / “Failed to enter command mode” errors would be greatly appreciated, as this is preventing me from proceeding with the telemetry setup.

Thank you!