Sony ST-88 - FM Alignment: Stereo Separation; Stereo Separation Adjustment Procedure; Stereo Separation Test Equipment and Preparation

ST-88 ac VTVM oscilloscope
fm oO ——“-"— 0 — 0
signal ANTENNA NORMAL OUTPUT IN
ma
er
generator
©
Jack
(J802)
Lo
Fig. 3-7. Fm frequency coverage and tracking alignment test setup
TABLE 3-2. FM FREQUENCY COVERAGE AND TRACKING ALIGNMENT
SG Coupling.....
re SG Output Level .. 400 Hz, 100 % mod; as low as possible
Step SG Frequency Dial Indication Ac VTVM Adjust Indication
Connection
87.5 MHz 87.5 MHz NORMAL OSC coil L103 Maximum
OUTPUT
See
Fig.
3-10.
VTIVM
2
108
MHz
108
MHz
jack
(J802)
FREQUENCY COVERAGE ALIGNMENT
reading
OSC trimmer CT103
See Fig. 3-10.
SG Coupling..... Direct
SG Output Level .. 400 Hz, 100 % mod; as low as possible
~~ TRACKING ALIGNMENT
87.5 MHz 87.5 MHz NORMAL
OUTPUT
jack (J802)
108 MHz 108 MHz
3-3. FM STEREO SEPARATION ADJUSTMENT
Maximum
VTVM
reading
Antenna coil L101
RF coil L102
See Fig. 3-10.
Antenna trimmer CT101
RF trimmer CT102
See Fig. 3-10.
Procedure:
1. Precisely tune the set to the carrier frequency of
stereo signal generator, then turn the top core of
switching transformer L301 (see Fig. 3-10) to
obtain maximum output at the left channel. Note
that this adjustment has a close relationship with
stereo distortion.
Test Equipment Required
1, Fm stereo signal generator
2. Ac VTVM
3. Oscilloscope
2. Record the output level of the left channel when
the stereo signal generator input selector is set to
the left channel.
Preparation:
1. Remove the wooden case as described in
Procedure 2-1 on page 2. k : ;
a 3. Switch the stereo signal generator input selector
. Connect the test equipment as shown in Fig. 3-8,
then set the fm stereo signal generator controls
as follows:
Carrier frequency ... 98 MHz
Output level.......- 1,000 nV (60 dB)
Mode ........-.-- Stereo
Audio (400 Hz) Mod . 67.5 kHz (90 %)
Pilot (19 kHz) Mod... 7.5 kHz (10 %)
Note: 75 kHz (100 %) if the metering indicates
total modulation (audio-pilot).
to the right channel and read the residual signal
level in the left channel.
. The output-level to residual-level ratio represents
the separation. Adjust separation adj. control
RV501 (see Fig. 3-10) for minimum residual level.
Check the right channel for separation. Usually,
about an 8 to 9 dB difference in channel separation
exists. Readjust RV501 for minimum difference
between left- and right-channel separation. While
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