I have 2 identical quads with an LW20 on the bottom and a TFmini in the front. I have the LW20 on serial1 and the TFmini on serial2. Both are powered from a 5v BEC. On the green build, both the TFmini and LW20 work flawlessly. On the yellow build, only the TFmini works. I verified all connections, and tried swapping RX/TX. Nothing makes the LW20 work on the yellow build. I verified the LW20 works with the lightware studio GUI. I tried moving the serial ports around and that also didn’t help. Anything else I can try in troubleshooting this?
What FMU are you using? Have you tried just connecting a radio or FTDI to the same serial port and set it to MAV to test it?
I have had a few Cube Blacks with dead serial ports.