Did you check to see if there's actually juice flowing into the bottom unit? I recently had a similar problem where T3 suddenly turned off. I wasn't even getting anything to light up on the LCD screen. I found the culprit to be a loose soldering in the EMI/RF suppression toroid wrapped in a black rubber heat shrink. It's a piece right before the power adapter attaches to the bottom unit. My unit gets cramped into a dash so I think that's how it got loose.