Section 3 Electrical Adjustments - Sony MDR-RF875RK Service Manual

Notes:
1. Use a transmitter to which check and adjustment are already
completed.
2. On adjusting the headphones section, use the transmitter as a jig.
Headphones:MDR-RF875R
Transmitter:TMR-RF875R
Procedure:
Connect an oscillator with attenuator and terminator (600 Ω)
1.
to the transmitter AUDIO IN-A connector (J402).
2. Connect an AC adapter to the transmitter DC IN 9V jack (J404).
3. Short between Q303 collector and GND on the RX board.
4. Connect DC 2.4V to the +B power line externally.
5. Connect lead wires to IC301 pin 4, pin 6, pin 7, IC 307 pin 7,
IC 308 pin 7 and GND on the RX-BASE board.
6. Connect a 33KΩ resistor between IC301 pin 4 and pin 7.
7. Connect lead wires to the speakers' terminals (L+,L-,R+,R-)
on the RX-BASE board. (See page 9)
3-1. Free Run Frequency Check and Adjustment
1. Set the transmitter AUDIO IN-A connector (J402) to no signal.
Note: In this case, operation time is about 4 or 5 minutes.
2. Check the transmitter power indicator (red) lights.
3. Set the transmitter CHANNEL switch to 1.
4. Connect DC 1.2V across TP and GND.
5. Connect a frequency counter to IC301 pin 4 and GND on the
RX-BASE board.
6. Adjust the value of the frequency counter to specification by
RV301 on the RX-BASE board.
Specified values: 76kHz ± 50Hz.
Setting :
Requlated power supply
(DC 1.2V)
TP
+
–
3-2. Receive Frequency Check and Adjustment
1. Set the transmitter CHANNEL switch to 2.
2. Set the transmitter NOISE FILTER switch to OFF.
3. Input a signal of 1kHz, 316mVrms to transmitter AUDIO IN-
A (L-ch) connector only.
4. Keep distance between transmitter and headphones to 5 meters over.
5. Set the headphones volume (RV302) to minimum.
6. Connect DC 1.2V across TP and GND.
7. Connect an oscilloscope CH1 and CH2 to IC301 pin 6 and pin 4.
8. Check the waveform of the oscilloscope to CH1 is demodulated
1kHz signal and CH2 is GND.
9. If CH1 and CH2 are not satisfied in step 8, adjust the coil (L301)
on the RX board to satisfied step 8.
10. Open between Q303 corrector and GND on the RX board.
11. When the transmitter off, check the waveform of the
oscilloscope as follows:
1.8V
2–3 sec
GND
12. Set the transmitter CHANNEL switch to 1.
13. Push the headphones tuning switch (S301) to receive radio
frequency.
14. Check same step 8.
15. Set the transmitter CHANNEL switch to 3.
16. Push the headphones tuning switch (S301) to receive radio
frequency.
17. Check same step 8.
SECTION 3
ELECTRICAL ADJUSTMENTS
Frequency counter
IC301 pin4
+
–
0.6V
Setting :
Requlated power supply
(DC 1.2V)
TP
+
–
3-3. Carrier Modulation Check
1. Set the transmitter CHANNEL switch to 2.
2. Set the transmitter NOISE FILTER switch to OFF.
3. Input a signal of 1kHz, 316mVrms to transmitter AUDIO IN-
A (L-ch) connector only.
4. Set the headphones volume (RV302) to minimum.
5. Connect an oscilloscope CH1 and CH2 to IC301 pin 6 and pin 4.
6. Push the headphones tuning switch (S301) to receive radio
frequency.
7. Check the waveform of the oscilloscope that the CH1 is
demodulated 1kHz signal and CH2 is GND.
8. Connect an AC voltmeter with LPF to IC301 pin 6 and GND.
9. Check the value of the AC voltmeter to 40mVrms ± 5mV
Setting :
Digital voltmeter
(AC range)
IC301 pin6
+
–
3-4. Expander Output Check
1. Set the transmitter CHANNEL switch to 2.
2. Input a signal of 1kHz, 316mVrms to transmitter AUDIO IN-
A L and R connector.
3. Connect an AC voltmeter to IC307 pin 7 and IC308 pin 7.
4. Measure the value of the AC voltmeter.
5. Input a signal of 1kHz, 31.6mVrms to transmitter AUDIO IN-
A L and R connector.
6. Measure the value of the AC voltmeter.
7. Check the difference of the step 4 and step 6 to more than 20
dB ± 3 dB.
Setting :
Digital voltmeter
(AC range)
IC307 pin7
+
–
IC308 pin7
3-5. Separation Check
1. Set the transmitter CHANNEL switch to 2.
2. Set the transmitter NOISE FILTER switch to OFF.
3. Input a signal of 1kHz, 316mVrms to transmitter AUDIO IN-
A (L-ch) connector only.
4. Connect an oscilloscope CH1 to speakers terminal (L+,L-) and
CH2 to IC301 pin 4 and GND.
5. Push the headphones tuning switch (S301) to receive radio
frequency.
6. Check the waveform of the oscilloscope that the CH1 is
demodulated 1kHz signal and CH2 is GND.
7. Connect an AC voltmeter with LPF to speakers terminal (L+,L-).
8. Adjust the value of the AC voltmeter to specification by
headphones volume RV302.
Specified values: 155mVrms
9. Connect an AC voltmeter with LPF to speakers terminal (R+,R-).
10. Measure the value of the AC voltmeter.
11. Check the difference of the L and R to more than 25dB.
12. Input a signal of 1kHz, 316mVrms to transmitter AUDIO IN-
A (R-ch) connector only.
— 7 —
OSCILLOSCPE
CH1 CH2
IC301 pin6 IC301 pin4
+ +
– –
OSCILLOSCPE
CH1 CH2
IC301 pin4
IC301 pin6
+ +
– –