"Same problem, different solution.
I could only arm my APM 2.8 when connected through a USB cable.
I got ~5v on both sides of the fuse, but only on the bottom (exterior) side of the diode. top (interior) side was dead.
I was looking at…"
"I'm having this same problem. Constant flash suggest it's ready to arm, but it won't. It will only arm when connected to USB (whether Mission Planner is running or completely closed out).
I checked voltage per the linked thread. Not getting…"