I have been looking into developing for the Wii U lately, I picked up a retail console, it's a nice device, I think it has a fantastic future, especially for developers.
However, my gamepad stopped working, dead, like RMA dead. It wouldn't charge, turn on, unplugging the battery had no effect.
Here is the deal, I think it's the AC Adapter, I think it's actually a smart charger, and for whatever reason, mine messed up while my device was plugged into it. I imagine if you are reading this post, it's because your gamepad doesn't work. Unplug your charger from both your gamepad and the wall socket, wait thirty seconds, plug the charger back into the wall and your gamepad. The power indicator should turn yellow and your device should turn on when you press the power button.
Some search terms to help fellow gamers.
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