Ive seen a few posts on the forum about power issues with the APM2.
I just had mine to the same thing when I was swapping input connections to a RX.
Ive looked into the schematics and the board and it looks as if there is a problem with the D1 diode that connects the power jumper / 5V Rail on the input connectors / board to the 5V rail on the output pins...
I think I have tracked down the specific device used and I have a concern... I believe this is the data sheet...
The problem is that the device is only rated at 30mA continuous forward current. Therefore if you are powering the unit via the output rail, the whole system cannot draw more than this (or a peak "surge" current of more than 500mA).
Has anyone else looked into or are aware this issue?
The other thing that Im now seeing is if I attach a standalone BEC to the 5V rail (via the input connections), the unit does not seem to boot up correctly. I have measured the output from the BEC and it seems to be 5.5V.
Does anyone know if this larger supply voltage (5.5V vs 5V) cause the unit not to operate correctly for some reason?