Sony MDX-C7900, Service Manual

Page: 18 / 62

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SECTION 4
ELECTRICAL ADJUSTMENTS
TEST MODE
This set have the test mode function. In the test mode, FM Auto
Scan/Stop Level and AM (MW) Auto Scan/Stop Level adjustments
can be performed easier than it in ordinary procedure.
<Set the Test Mode>
1. Set the “power select” switch (S700) is “A (ON)” position.
2. Turn ON the regulated power supply. (All LEDs on the set
lights up, and the clock is displayed.)
Note:
Press the
[OFF]
button, if the clock is not displayed.
3. Push the preset
[4]
button.
4. Push the preset
[5]
button.
5. Press the preset
[1]
button for more than two seconds.
6. Then the display indicates all lights, the test mode is set.
<Release the Test mode>
1. Push the
[OFF]
button.
2. Return the “power select” switch (S700) to initially set posi-
tion.
MD SECTION
MD section adjustments are done automatically in this set.
TUNER SECTION
Note:
Adjust the tuner section in the sequence shown below.
1. FM Auto Scan/Stop Level Adjustment.
2. FM Stereo Separation Adjustmnet.
3. AM (MW) Auto Scan/Stop Level Adjustment.
4. RDS S-Meter Adjustment.
FM Auto Scan/Stop Level Adjustment
Setting:
[SOURCE]
button: FM
Procedure:
1. Set to the test mode.
2. Push the
[SOURCE]
button and set to FM.
Display
0 dB=1 µV
See the adjustment location from on page 20 for the ad-
justment.
Cautions during repair
When the tuner unit is defective, replace it by a new one be-
cause its internal block is difficult to repair.
3. Adjust with the volume RV2 on TU1 so that the “FM” indica-
tion turns to “FM0” indication on the display window.
But, in case of already indicated “FM0”, turn the RV2 so that
put out light “0” indication and adjustment.
Display
*1: MDX-C7900R is indicates “98.00”.
Adjustment Location: See page 20.
FM Stereo Separation Adjustment
Setting:
[SOURCE]
button: FM
Procedure:
L-CH Stereo separation:
A
-
B
R-CH Stereo separation:
C
-
D
The separations of both channels should be equal.
Specification: Separation more than 30 dB
Adjustment Location: See page 20.
FM RF signal
generator
Carrier frequency: 97.9 MHz (MDX-C7900)
98.0 MHz (MDX-C7900R)
Output level : 22 dB (12.6
µ
V)
Mode : mono
Modulation : 1 kHz, 22.5 kHz deviation (30%)
0.01
µ
F
set
antenna jack (J1)
SHUF
REG
*1
SHUF
REG
*1
FM RF signal
generator
0.01
µ
F
set
antenna jack (J1)
+
–
speaker out terminal
level meter
4
Ω
MDX-C7900 MDX-C7900R
Carrier frequency 97.9 MHz 98.0 MHz
Output level 60 dB (1 mV) 70 dB (3.2 mV)
Mode stereo stereo
main
1 kHz, 33.75 kHz 1 kHz, 20 kHz
deviation (45%) deviation (22.6%)
Modulation sub
1 kHz, 33.75 kHz 1 kHz, 20 kHz
deviation (45%) deviation (22.6%)
19 kHz 7.5 kHz 7.5 kHz
pilot deviation (10%) deviation (10%)
FM Stereo
Level meter Level meter
signal generator
connection reading (dB)
output channel
L-CH L-CH
A
B
R-CH L-CH Adjust RV4 on TU1
for minimum reading.
R-CH R-CH
C
D
L-CH R-CH Adjust RV4 on TU1
for minimum reading.