Hello,
On my RN-602 The Temperature Sensor (IC) was open.
Look for a small board touching the heat sink (LM19 2.4V, 10μA, TO-92)
I dint replace the transistor, I just bypass it by jumping (+Vs 3.3vdc et V-out)
You also need to do a reset.
While pressing DIMMER and PRESET buttons, press the power button to activate the self drag mode.
Full drawing here.
[link|https://www.manualslib.com/manual/1866726/Yamaha-R-N602.html?page=43#manual|https://www.manualslib.com/manual/1866726/Yamaha-R-N602.html?page=43#manual|new_window=true]
Hope this helps you.
[image|3302332]