"Yeah, I had this problem and I couldn't figure it out more than year by ordering many different power modules, but in result problem wasn't with power modules  but with my CHEAP EBAY PIXHAWK!!!
Please don't buy any NoBrand pixhawk from ebay,…"

"Same problem, tried many power modules.. still experiencing this problem. Hope someone could help. I have Micro APM from HobbyKing and Pixhawk both using different power modules, both of them have same problem described here. Can't figure out…"

"Big thanks to YOU! After many days, after reading your post I finally fixed minimosd updating problem. What I done - Upgraded minimosd to Arducam 2.0  Firmware using 1.9 charset. What it do is on boot up requesting data from APM, so TX wire should…"