Those measurements on the LINE OUT (while playing back the recorded signals) are done with unit sitting normal or upside down ? How do they vary with orientation ? Regarding the bias signal measurement, easier way to measure it is at the adjustment capacitors (at the adjustment pads on back of the board) relating to GND rather than at the head. However given this signal is high frequency (85kHz) your multimeter may not be able to measure it.
The unit was sitting normal. This morning I've redone the measurements with the unit sitting normal and upside down. Like yesterday when it was sitting normal (strangely) the rec level on the R and L channel were similar to one another (the R channel sightly quieter but not much), while when it was upside down the R channel became quieter than the L one (From 270mV at 300Hz sitting normally to 80mV upside down. This behavior is the opposite of what have happened until now). The behavior between the 3 frequencies remained the same (at 300hz the max AC V, than a slight reduction on 1kHz and lastly a big reduction at 10kHz). I've tried to measure the kHz at the adjustment capacitors: R channel 78,23kHz, L channel 78,30kHz.
