Someone gave me a Bowers & Wilkins A7 wireless speaker, and I'm trying to figure out how to diagnose and fix it. It works great for about 20 minutes, then starts flashing red, which means it's in "protect mode" and needs to be sent into the manufacturer for repair. Unplugging the power for a few seconds is enough to reset it, then it works again. I'm guessing maybe something is overheating? Visually inspecting the capacitors inside, I don't see anything wrong. What's the next step to find the problem?