BERINGER EURORACK MX1604A MIXER Right Channel Have Lower output then to the Left side

Hello Sir,
I'm Sandy Here,
sir I have a BERINGER EURORACK Mx 1604a Mixer..so the problem is that left side output is Properlly  in Good Condition bt The Right one outs have some lower sound then Left in (4dbu) bt If I push back the switch in Line the Right and Left outputs is Good So whats d is going on in thatz mixer sir can yew tell me please..        
 
       
                          Thank you..