If the bias is too high despite the position of R20 on both channels (rare) check to see if the board is grounded between D11 and D12 at 5L1. If the bias is high one channel, check for zero volts on the base of Q6 at "B-L" or "B-R". Then check for 1.6 volts on the collector of Q6 at "C-L" or "C-R" and negative .7 volts on the emitter of Q6 at "E-L" or "E-R". If these voltages are not present or incorrect, replace Q6 on the affected channel.