This appears to be an issue with the power module. Here is a plot of the voltage measured at the power module port, and at the servo rail where the ESCs connect. Both values should be a steady ~5V. The pixhawk is reading more than 6.5V on the power supply, this is why you had the warning when you attempted to arm.
It looks like something is failing with the power module causing the reference voltage to be incorrect, then the power module fails completely or disconnects, and the pixhawk is now powered by the servo rail with the correct reference voltage.
What I recommend you do now:
- Unplug the connector that is plugged into the ‘Power’ port on the Pixhawk.
- Power on the ROV, and get a short telemetry log while the Pixhawk is not connected to the power module to verify that the Pixhawk is functioning correctly.
- Measure the voltages on the power module connector that you unplugged to verify the issue. Here is the pinout:
- Contact email@example.com for replacements.