Just the I2C stuff changed, which in theory should not affect the tuner at all. But somehow it does. v505 is fine according to Ben (the OP), yet v506 does not seem to have working AGC on his tuner.

The only changes there are all I2C stuff -- I added (heretofore missing) locking to the driver, and tightened up the timing here and there. This mostly affects the DSP chip, which is used for just about everything inside an empeg.

The tuner is controlled by an unrelated serial port.

Cheers