Ensure the unit has at least 3 inches of clearance on top for thermal ventilation.
Turn off the unit immediately. Check all speaker terminals for stray wire strands. Ground loop via cable box or turntable. harman kardon avr 51 user manual 134 upd
Maintain at least 3 inches (7.6 cm) of clearance above the top chassis. Do not block the cooling vents. Ensure the unit has at least 3 inches