I've been testing my purple board through the USB and it works good enough to replace an ArduPilot Mega 1 on an EasyStar. Everything is connected and the power jumper is in so the ESC is supplying system power.
But, the APM2 will not start up on either ESC or UBEC power. Even wired in, it still boots on the USB power, as it has always done. The APM1 never had any problems with power on this plane and another APM1 always works on a T-28.
Has anyone seen this problem with ESC/UBEC power?