Cary V12r with balance unequal when in bias

My Cary V12, when biased with the leds, has an imbalance of output volume. I tried switching input cables, eliminating the preamp and using different input sources, no vinyl. I also swapped tubes from left to right, including the input and current tubes at different times. Everytime the left channel is louder. When I turn down the bias until the balance is equal, all of the left channel leds go unlit. What could be the issue? Thanks all for your input ahead of time.