Official comment
In the majority of cases where users had reported this issue, it turns out that they ran their mixer into another console which supplied phantom power up the outputs, thus frying the output board in the DJM.
If this was a problem when you purchased it but have now passed the warranty, I'm sorry but the repairs would be at your expense - hindsight is 20/20, but I would have either returned it to the retailer immediately or sought a repair.
Please contact a Pioneer DJ authorized service centre in your region to have your hardware inspected and/or repaired.