Fm Tuner; T U N E R S E C T I O N - Pioneer SX-3900 Service Manual

8 . 2 T U N E R S E C T I O N
F M T u n e r
o Connect the FM SG (FM signal generator) to
the FM ANTENNA 300Q terminals via a 300O
dummy antenna.
o Switch the FUNCTION selector to the FM posi-
tion, the FM MUTING OFF switch to the OFF
position.
o L5 and L6 are coreless coils which may be
adjusted by extending one turn of coil out to-
wards tuning capacitor (see Fig. 8-2).
1. Set the SX-3900 dial pointer to a frequency in
the 106MHz region so that there will be no
input signal.
2. Rotate the N core of T2 so that the voltage
between no.B and no.7 terminals on the tuner
assembly is reduced to DC 0V.
3. Next tune the dial pointer to 106MHz, and set
the FM SG outPut to 106MHz, 60 to 80dB
(modulation - 40OHz, t71kHz deviation).
4. Adjust TC1 so that the voltage between no.8
and no.7 terminals is reduced to DC 0V and
maximum reading of the SIGNAL indicator.
5. Then tune the dial pointer to 90MHz, and set
the FM SG output frequency to 90MHz.
6. Rotate the L8 core so that the voltage between
no.B and no.? terminals is reduced to DC 0V
and maximum reading of the SIGNAL indica-
tor.
7. Repeat steps 3 to 6 above.
8. Reset the FM SG output level to 20
- 30dB'
and adjust "1C2, "1C3, TC4 and T1 at 106MHz,
and L2, L5 and L6 at 90MHz in the same man-
ner as described in steps 3 to 7. These adjust-
ments will ensure optimum sensitivity between
the two extreme frequencies.
9. Retune to a position with no input signal.
10. Rotate the A core of T2 so that the voltage
between no.8 and no.7 terminals is reduced to
DC OV.
11. Set the FM SG output to 98MHz and 60dB
(modulation - 4O0Hz, x7lkHz deviation), and
tune the SX-3900 to this position (fine adjust
the tuning knob to ensure a DC 0V reading
between no.8 and no.7 terminals).
12. Then rotate the B core of T2 to reduce distor-
tion in the demodulator output (TAPE REC
terminal) to minimum.
13. Repeat steps 9 to 12 above until both specifica-
tions are satisfactorilY met.
14. Set the FM SG output to 98MHz and 60dB,
and tune the SX-3900 to this position.
1-5. Adjust VR2 so that the SIGNAL indicator
(5-point display) reads "5".
16. Turn the FM MUTING OFF switch to the ON
position, and set the FM SG output level to
20d8.
17. Adjust VR1 to bring the input level to the
starting point of the muting operation.
MultiPlex Decoder
o Connect the MPX SG (FM multiplex generator)
to the FM SG external modulator terminal.
o Set the FM MUTING OFF switch to the OFF
position.
18. Set the FM SG output to 98MHz and 60dB
(unmodulated), and tune the SX-3900 to this
position (fine adjust the tuning knob to ensure
a DC 0V reading between no.S and no.7 ter-
minals).
19. Adjust VRb to obtain a 76kHz signal at termi-
nal no.6.
20. Set the FM SG output level to 60dB, and the
modulation mode to external. Then with the
MPX SG, set Main off, and pilot signal to
t7 .lkHz deviation.
21. Adjust VR4 to reduce leakage of the 19kHz
pilot signal (in both channels) to a minimum
(at TAPE REC terminals).
22.Set the FM SG output level to 80dB, the MPX
SG Main to 1kHz, L+R to t67.1kHz deviation,
and pilot signal to !7 .1kHz deviation.
23. Rotate the T1 core around by up to 90' in
either direction to reduce the demodulator
output (TAPE REC terminals) distortion to a
minimum.
24. Then set the FM SG output level to 60dB, the
MPX SG Main to 1-kHz, L (or R) to 133'75kHz
deviation, and pilot signal to x7.1kHz devia-
tion.
25. Adjust VR4 to reduce crosstalk between L and
R channels to a minimum.
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