Sony TA-F60 right channel not work

I have an old Sony TA-F60 amplifier. It works fine recently. But yesterday, I detected the right channel did not work any more. I open and check the power amply board and detect that the voltage at the C of Q213 and Q214 = -8V. I turn the RT201 to adjust the balance but it can not reach 0V, just -8V.
The voltage at .22R is 18mV for Q213 and Q214.
Please advice me to fix this issue. 
Thank you in advance. 
Tu Trong