Sony TC-730 Service Manual page 30

11. Reverse Bias
Frequency
Adjustment
checking point
record
playback Sar amp
amp circuit bias osc circuit
board circuit board , board
C) a) le @
Control Setting:
Record volume controi
fully counterclockwise
Specification:
Less than -10 dB
Note: Perform after the trap coil adjustment.
12. Record Bias
Adjustment
Test Setup:
blank tape
AF osc REC Amp
MIC jack
LINE OUT jack
Control/Switch Setting:
*Record volume control
specified position on page 25
*MONITOR switch
Specification:
*0 +1dB....
*042dB....
at peak bias point
playback output of 18 kHz sig-
nal against that of 1 kHz signal
Note: The adjustment should be performed for
both L-CH and R-CH in forward and reverse
modes.
—~32-—
(1) Place the unit in the reverse-stereo record mode.
(2) Adjust C509 so that the VTVM reads a minimum
(less than —10 dB).
Note: If the minimum value for both channels can
not be obtained at the same angle of the
trimmer capacitor, take the mid between the
two angles.
After the adjustment, make sure that the
VTVM reads less than —10 dB.
(3) Apply lock paint to the trimmer capacitor.
Turn C510, C511, C512 and C513 clockwise to
the full and return them approximately three
times.
Thread a blank tape.
Deliver a 1 kHz signal of —80 dB (77.5 LV) to
the MIC jack.
Place the unit in the stereo-record mode.
Slowly, turn C510, C511, C512 and C513 clock-
wise, and the VIVM reading will go up and reach
a maximum.
So note the VIVM reading.
C510 (L-CH forward run)
C511 (R-CH forward run)
C512 (L-CH reverse run)
C513 (R-CH reverse run)
Change the input signal frequency from | kHz to
18 kHz.
Turn C510, C511, C512 and C513 further clock-
wise so that the VTVM reading is the same as the
value noted in the step (5).
Note: Make sure that the VTVM reading does not
fall more than 1 dB from the maximum
output obtained in the step (5).
(8) Apply lock paint to the trimmer capacitors.