Bench testing requires a
CAN BUS recording from a car being played into the unit, depending on the unit (firmware) it might turn on for 10 seconds when power is initially applied (after 20 seconds). My one from 2012 doesn't even do that, the one I've replaced mine with does - it's a 2014 model with newer firmware. What's yours?
If I didn't have the
CAN BUS stuff, I would be testing the voltages while in the car.
You can see where the 20v and 11v are coming from, on the small circuit board. I don't think it's hard to measure those while in the car, as long as it's been unscrewed from the back cover.
It might be obvious from a picture, as you said, there's residue on yours?