The processor is no longer available,but rarely fails anyway,it's usually upset by faulty anciliary components.Try taking the batteries out of the handset to disable remote control.The handset keyboard can become conductive around the most used keys.If the Beomaster functions normally via it's own controls,it could be the handset sending spurious commands,causing the problem
The ir receiver in the Beomaster can become "noisy",and can cause the same above effects
The motorised volume control is notorious for becoming sluggish or sticking,usually due to a slack belt,but also can be due to a dodgy motor(worn brushes)
Other possible causes are poor grounding of the volume control as Martin suggests.This could cause max volume without the control moving,ie no volume level display,but max output,or "11"
Lovely piece of kit,well worth sorting.
Regards,
Nick