Konica Minolta magicolor4690MF fan staying on

[pcs]

I have a customer with a Konica Minolta magicolor4690MFP and the ozone fan comes on and goes off periodically, which it does when it is not being used. But from time to time the fan stays on and when this happens the unit is none functional no buttons work and you have to power cycle the unit.

I have gone through the service manual and checked out the unit and there does not seem to be anything wrong.

The unit is not used that much less then 500 pages per month

Any ideas would be helpful.

Thanks