Check the rear speaker terminals for stray copper wire strands touching the chassis.
What (2.0 stereo, 5.1 surround) do you currently run? harman kardon avr 51 user manual 134 better
: If the unit becomes unresponsive, check the back panel for a reset button (common in many Harman Kardon models) and hold it for 5+ seconds. Check the rear speaker terminals for stray copper
: The full owner's guide can be found on the Harman Kardon Support Site . ⚠️ Important Setup Tips Harman/Kardon AVR-51 - Classic Audio : The full owner's guide can be found
Coaxial and Optical (Toslink) inputs for digital audio decoding. 2. Essential Front Panel Operations
Some late-production AVR 51 units shipped with DSP firmware version 1.34. This revision improved and fixed a “center channel dropout” issue. If your unit has firmware 1.34, you are already running a better, more reliable version than early models.