Arcam 8R amplifier non direct sound distorted

I have an Arcam 8r amp. It sounds ok when I have the direct button on for the speakers but when I click it off so I can use, bass, treble and balance it is all distorted.

What should I suspect of gone wrong please ?

I have 2 more so I can swap parts but if you can lead me to the right direction where to start.

Distortion is on both channels and I kind of hear the audio moving from left to right if o use the balance control.
 

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