Yamaha Tyros 5 right channel fail

Hi

My Tyros 5 plays nicely through both channels for a short time. After maybe 10 mins the right channel cuts out. Fault common to jacks on the back and headphone socket. The right channel can be heard hissing slightly so the amp isn’t dead. Power down and back and the right channel returns again for 5 to 10 mins. Obvious things like speakers have been swapped. Any ideas?