I need help with my Yamaha it cuts off every time it's powered on for more than 30 minutes sometimes an hour I'm pretty sure the fan is not turning on I took it apart and got it working again but after an hour it turned off but I've been using it at very low volume settings I haven't tried to use it since cause I'm afraid I'm going to do damage does anybody know how I can get the fan to start working properly again please and thank you for the help in reading this .Yamaha RX-Z1