USB OTG port not working?

jerms

I've been trying very hard to follow the instructions to flash the firmware on my Firefly RK-3288. However, nothing I try seems to work. I've tried every sequence of button presses, long presses on the power, starting with it unplugged, etc., and it never enters loader mode. The device always boots up normally and the Linux flash tool never sees it. I'm starting to think that maybe there's a problem with the OTG port. I tried to use adb over USB when it was booted into Android, and that does not work either. ADB on the host computer does not see any connected devices. Does anyone have any tips for debugging this?