I have the exactly same issue with my NU7400. After switching on the tuner of my AV receiver, which is connected to my Samsung TV via ARC HDMI, the receiver obviously gets a signal from the TV to power off after about 2 minutes. When I turn on the receiver (tuner) again, it stays on. I'm sure that the TV sends a signal, because when I disconnect the ARC HDMI cable, the receiver doesn't turn off in tuner mode automatically. Latest TV firmware installed.
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