Audio is present but weak, fuzzy, harsh, or distorted.
Safe first checks
Reduce the volume immediately if distortion is severe.
Test a different source and a different pair of speakers if available.
Confirm that Tape Monitor, loudness, filters, and speaker switches are set as intended.
Do not continue operating the unit if it becomes hot, smells burnt, or repeatedly enters protection.
Next step
Note whether distortion begins at low volume, affects both channels, and changes when a control is moved.
Bench Technician Steps
This is the model of work a qualified electronics technician follows using the exact service manual and suitable test equipment. It is not a do-it-yourself instruction to work on energized equipment.
Use a known-good signal source and trace the signal path methodically from the input stage toward the output, following the model-specific block diagram or service manual.
Compare left and right channel voltages and signal behavior at equivalent points where the design has mirrored channels.
Verify switches, relay contacts, connectors, and board interconnects before replacing active parts.