Sony XR-3750 User manual

MICROFILM
SERVICE MANUAL
FM/MW/SW CASSETTE CAR STEREO
Saudi Arabia Model
Model Name Using Similar Mechanism XR-4800
Tape Transport Mechanism Type MG-25F-136
SPECIFICATIONS
XR-3750

– 2 –
TABLE OF CONTENTS
1. GENERAL
Location of Controls ....................................................... 3
Resetting the Unit ........................................................... 4
Detaching the Front Panel............................................... 4
Setting the Clock ............................................................. 4
Dismounting the Unit...................................................... 4
Installation....................................................................... 5
Connection ...................................................................... 6
2. DISASSEMBLY ......................................................... 8
3. ASSEMBLY OF MECHANISM DECK........... 10
4. MECHANICAL ADJUSTMENTS....................... 13
5. ELECTRICAL ADJUSTMENTS
Test Mode ........................................................................ 13
Tape Deck Section .......................................................... 13
Tuner Section .................................................................. 14
6. DIAGRAMS
6-1. IC Pin Function Description ........................................... 17
6-2. Note for Printed Wiring Boards and
Schematic Diagrams ....................................................... 20
6-3. Printed Wiring Board – MAIN Section – ...................... 21
6-4. Schematic Diagram – MAIN Section (1/2) –................. 23
6-5. Schematic Diagram – MAIN Section (2/2) –................. 25
6-6. Printed Wiring Board – PANEL Section – .................... 27
6-7. Schematic Diagram – PANEL Section – ....................... 29
7. EXPLODED VIEWS................................................ 33
8. ELECTRICAL PARTS LIST ............................... 36
Flexible Circuit Board Repairing
• Keep the temperature of the soldering iron around 270 ˚C dur-
ing repairing.
• Do not touch the soldering iron on the same conductor of the
circuit board (within 3 times).
• Be careful not to apply force on the conductor when soldering
or unsoldering.
Notes on chip component replacement
• Never reuse a disconnected chip component.
• Notice that the minus side of a tantalum capacitor may be dam-
aged by heat.

– 3 –
SECTION 1
GENERAL This section is extracted from
instruction manual.

– 4 –

– 5 –

– 6 –

– 7 –

– 8 –
COVER ASS’Y
SUB PANEL, MECHANISM DECK (MG-25F-136)
Note: Follow the disassembly procedure in the numerical order given.
SECTION 2
DISASSEMBLY
1
1
1
2
2
2
3 cover ass’y
3 connector
(CN351)
2 sub panel
1 three screws
(PTT2.6
× 8)
1 three screws
(PTT2.6
× 8)
5 screw
(PTT2.6
× 6)
6 mechanism dec
k
(MG-25F-136)
4 flexible flat cable
(CN301)

– 9 –
MAIN BOARD, HEAT SINK
3 two ground point
screws
5 two screws
(PTT 2.6
× 8)
5 three screws
(PTT 2.6
× 10)
1 screw
(PTT2.6
× 8)
5 two screws
(PTT 2.6
× 8)
6 heat sink
2 rubber cap (25)
1 two screws
(PTT2.6
× 8)
4 main board

– 10 –
SECTION 3
ASSEMBLY OF MECHANISM DECK
HOUSING
ARM (SUCTION)
Note: Follow the disassembly procedure in the numerical order given.
1 Install the catch to the hanger.
7 Holder the hanger by bending the claw.
6 Fit projaction on D part.
4 Fit claw on B part.
5 Fit projection on C part.
2 Install the hanger onto
two claws of the housing.
3 Put the housing
under
A part.
D part
B part
A part
C part
8 Hold the hanger by
bending the claw.
hanger
housing
2 Move the arm (suction) in the arro
w
direction and fit on projection.
1 Fit the arm (suction) on the shaft.
projection

– 11 –
LEVER (LDG-A) / (LDG-B)
GEAR (LDG-FT)
shaft A
shaft B
shaft C
1 Fit the lever (LDG-A) on
shafts A – C and install it.
3 type-E stop ring 2.0
shaft
B
shaft A
2
Fit the lever (LDG-B) on
shafts
A and B and
install it.
4 Align hole in the gear (LDG-D)
with hole the lever (LDG-A)
5 gear (LDG-FT)
6 polyethylene washer
3 Move the lever (LDG-B)
in the arrow direction.
2 tensiton spring (LD-1)
2 tensiton spring (LD-2)
gear (LDG-FB)
lever (LDG-A)
hole
hole
gear (LDG-D)
1

– 12 –
GUIDE (C)
2 guide (C)
1 three claws
MOUNTING POSITION OF CAPSTAN / REEL MOTOR (M901)
two precision screws
(P2
× 2)
capstan / reel moto
r
(M901)
30˚

– 13 –
SECTION 4
MECHANICAL ADJUSTMENTS SECTION 5
ELECTRICAL ADJUSTMENTS
1. Clean the following parts with a denatured-alcohol-moistene
swab:
playback head pinch roller
rubber belt capstan
idler
2. Demagnetize the playback head with a head demagnetizer.
3. Do not use a magnetized screwdriver for the adjustments.
4. After the adjustments, apply suitable locking compound to the
parts adjusted.
5. The adjustments should be performed with the power supply
voltage unless otherwise noted.
•Torque Measurement
Mode Tension Meter Meter Reading
Forward CQ-403A more than 90 g
(more than 3.18 oz)
Reverse CQ-403R more than 90 g
(more than 3.18 oz)
•Tape Tension Measurement
TEST MODE
This set have the test mode function. In the test mode, FM Auto
Scan/Stop Level andAM (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 (S501) is “A” 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 (S501) to initially set posi-
tion.
See the adjustment location from on page 16 for the
adjustment.
0 dB=0.775 V
TAPE DECK SECTION
Tape Speed Adjustment
Setting:
Speed checker Frequency counter
–1.5 to +2.5% 2,955 to 3,075 Hz
Procedure:
1. Put the set into the PB mode.
2. Adjust adjustment resistor for inside capstan motor so that the
reading on the speed checker or frequency counter becomes in
specification.
Specification: Constant speed
Adjustment Location: See page 16.
set +–
test tape
WS-48A
(3 kHz, 0 dB)
LINE OUT
10 k Ω
speed checker
or
frequency counter
Mode Torque Meter Meter Reading
Forward CQ-102C 30 – 65 g•cm
(0.42 – 0.90 oz·inch)
Forward CQ-102C 0.5 – 4.5 g•cm
Back Tension (0.01 – 0.06 oz·inch)
Reverse CQ-102RC 30 – 65 g•cm
(0.42 – 0.90 oz·inch)
Reverse CQ-102RC 0.5 – 4.5 g•cm
Back Tension (0.01 – 0.06 oz·inch)
FF, REW CQ-201B 60 – 200 g•cm
(0.83 – 2.78 oz·inch)

– 14 –
TUNER SECTION
98.0
SHUF1
Cautions during repair
When the tuner unit is defective, replace it by a new one be-
cause its internal block is difficult to repair.
Note:
Adjust the tuner section in the sequence shown below.
1. FM Auto Scan/Stop Level Adjustment
2. FM Noise FocusAdjustment
3. FM Stereo Separation Adjustment
4. AM (MW) Auto Scan/Stop Level Adjustment
FM Auto Scan/Stop Level Adjustment
Setting:
[SOURCE] button: FM
Procedure:
1. Set to the test mode. (See page 13)
2. Push the [SOURCE] button and set to FM.
Display
3. Adjust with the volume RV2 on TU1 so that the “FM” indica-
tion turns to “FMI” indication on the display window.
But, in case of already indicated “FMI”, turn the RV2 so that
put out light “I” indication and adjustment.
Display
Adjustment Location: See page 16.
FM RF signal
generator
Carrier frequency : 98.0 MHz
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)
FM 98.0
SHUF1
0 dB=1 µV
FM Noise Focus Adjustment
Setting:
[SOURCE] button: FM
Procedure:
1. Tune the 98.0 MHz.
2. The then output level is supposing that (A) dB.
3. Adjust with the volume RV3 on TU1 so that the output level is
(A) –32 ± 2 dB then signal generator input set to –20 dB.
Adjustment Location: See page 16.
FM Stereo Separation Adjustment
Setting:
[SOURCE] button: FM
Procedure:
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.
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 16.
FM RF signal
generator
Carrier frequency : 98.0 MHz
Output level : 60 dB (1 mV)
Mode : mono
Modulation : 1 kHz, 75 kHz deviation (100%)
0.01 µ F
set
antenna jack (J1)
+
–
LINE OUT
level meter
10 k
Ω
FM RF signal
generator
Carrier frequency : 98.0 MHz
Output level : 60 dB (1 mV)
Mode : mono
Modulation : 1 kHz, 75 kHz deviation (100%)
0.01 µ F
set
antenna jack (J1)
+
–
LINE OUT
level meter
10 k
Ω

– 15 –
AM (MW) Auto Scan/Stop Level Adjustment
Make this adjustment after “FMAuto Scan/Stop Level Adjustment”.
Setting:
[SOURCE] and [MODE] button: MW
AM RF signal
generator
Carrier frequency : 999kHz
30% amplitude
modulation by
1 kHz signal
Output level : 33 dB (44.7
µ
V)
(50 Ω )set
AM dummy antenna
30 Ω
15 pF
65 pF
antenna jack (J1)
Procedure:
1. Set to the test mode. (See page 13)
2. Push the [SOURCE] button and set to FM.
3. Push the [MODE] button and set to MW.
Display
MW
999
SHUF1
INTRO
4. Adjust with the volume RV1 on TU1 so that the “MW” indica-
tion turns to “MWI” indication on the display window.
But, in case of already indicated “MWI”, turn the RV1 so that
put out light “I” indication and adjustment.
Display
999
SHUF1
INTRO
Adjustment Location: See page 16.

– 16 –
Adjustment Location:
– SET UPPER VIEW –
Tape Speed Adjustment
TU 1
RV 1 AM (MW) Auto Scan/Stop Level Adjustmen
t
RV 2 FM Auto Scan/Stop Level Adjustment
RV 3 FM Noise Focus Adjustment
RV 4 FM Stereo Separation Adjustment

– 17 –
6-1. IC PIN FUNCTION DESCRIPTION
SECTION 6
DIAGRAMS
•MAIN BOARD IC501 µPD17708GC-545-3B9 (SYSTEM CONTROLLER)
Pin No. Pin Name I/O Function
1 ILLIN I Dimmer detection signal input terminal Dimmer is present at input of “L” (fixed at “L”)
2 POS3 I
3 POS2 I
4 POS0 I
5 POS1 I
6 TAPEON O Tape system power supply on/off control signal output terminal “H”: tape on
7 CM ON O Capstan/reel motor (M901) drive signal output terminal “H”: motor on
8 LM LOD O Loading/tape operation motor control signal output to the MM1322XFBE (IC351)
(For the loading direction and forward side operation) *1
9 LM EJ O Loading/tape operation motor control signal output to the MM1322XFBE (IC351)
(For the eject direction and reverse side operation) *1
10 TUNON O Tuner system power supply on/off control signal output to the BA3918 (IC611) “H”: tuner on
11 FM ON O FM system power supply on/off control signal output to the BA3918 (IC611) “H”: FM on
12 PW ON O Main system power supply on/off control signal output to the BA3918 (IC611) “H”: power on
13 MUT O Line muting control signal output terminal “H”: line muting on
14 VOLCE O Chip enable signal output to the electrical volume (IC331)
15 VOLCKO O Serial data transfer clock signal output to the electrical volume (IC331)
16 VOLSO O Serial data output to the electrical volume (IC331)
17 AMPON O Standby control signal output to the power amplifier (IC751) “L”: standby
18 AMPMUT O Muting control signal output to the power amplifier (IC751) “L”: muting on
19 DX/LO O Local/DX selection signal output to the FM/AM tuner unit (TU1) “L”: DX, “H”: local
20 AM MONO O AM forced monaural signal output terminal Not used (open)
21 GND — Ground terminal
22 DSTSEL I Destination setting terminal (Fixed at “L” in this set)
23 DBASIN I D-BASS switch (SW951) input (A/D input)
24 KEYIN1 I Key input terminal (A/D input) LSW921 to LSW927
(6, INTRO 1, REPEAT 2, 3, BL. SKIP 6, ATA 5, 4 keys input)
25 KEYIN0 I Key input terminal (A/D input) LSW901 to LSW909, 911, 912, 930 (OFF, SOURCE, MODE *, + +)SEEK AMS, =0– SEEK AMS, VOLUME –,
SEL, VOLUME +, MUTE , BTM, LCL, DSPL keys input)
26 RC IN0 I Rotary remote commander shift key A/D input terminal
27 VSM I FM and AM signal meter voltage detection input from the FM/AM tuner unit (TU1)
28 AMIFIN I AM intermediate frequency detection signal input from the FM/AM tuner unit (TU1)
29 FMIFIN I FM intermediate frequency detection signal input from the FM/AM tuner unit (TU1)
30 VDD2 — Power supply terminal (+5V)
31 FM OSC I FM local oscillator detection signal input from the FM/AM tuner unit (TU1)
32 AM OSC I AM local oscillator detection signal input from the FM/AM tuner unit (TU1)
33 GND — Ground terminal
34 NCO O Not used (open)
35 EO1 O Main charge-pump control signal output terminal
36 TEST0 I Setting terminal for the test (fixed at “L”)
37 AM STIN I Not used (open)
38 SEKOUT O Seek control signal output to the FM/AM tuner unit (TU1)
39 MW/SW O MW/SW selection signal output to the FM/AM tuner unit (TU1) “L”: MW, “H”: SW
40 BEEP O Beep sound output terminal
41 KEYACK I Input of acknowledge signal for the key entry Acknowledge signal is input to accept function
and eject keys in the power off status On at input of “H”
Tape position detect input from tape operation switch on the mechanism block

– 18 –
Pin No. Pin Name I/O Function
42 BU IN I Battery detect signal input terminal “H”: battery on
43 MTLSEL I/O
44 DOLON I/O
45 AMSIN I Whether a music is present or not from CXA2509AQ (IC301) is detected at auto music sensor
“L”: music is present, “H”: music is not present
46 ST I/O
47 AMS ON O Tape auto music sensor control signal output to the CXA2509AQ (IC301)
“L” is output to lower the gain for audio level at FF/REW
48 N/R OUT O Forward/reverse direction control signal output to the CXA2509AQ (IC301)
“L: forward direction, “H”: reverse direction
49 TAPMUT O Tape muting on/off control signal output to the CXA2509AQ (IC301) “H”: tape muting on
50 ILLON O
51 SD IN I Station detector detect input from the FM/AM tuner unit (TU1)
Stop level for SEEK, BTM, etc. is determined SD is present at input of “H”
52 NOSESW I Detects the removal of the attaching and removing type front panel block “L”: attaching
53 TELMUT I Telephone muting signal input terminal At input of “L”, the signal is attenuated by –20 dB
54 REL T I Reel table rotation detect signal input from the take-up and supply reel sensor
55 ACCIN I Accessory detect signal input terminal “L”: accessory on
56 TESTIN I Setting terminal for the test mode “L”: test mode (normally fixed at “H”)
57 RC IN1 I Rotary remote commander shift key A/D input terminal
58 PW SEL I Power select switch (S501) input terminal
“L”: position A (halt mode), “H”: position B (operation mode)
59 MTLIN I Input terminal to set whether the auto metal function is present or not
“L”: auto metal function is present (fixed at “H”)
60 ADON O Power supply on/off control signal output for the A/D conversion
61 KEYSEL I Setting terminal for the key (fixed at “H”)
62 SEKOUTSEL I Active selection terminal for the SEKOUT (pin #•) (fixed at “L”)
63 COLORSEL I Setting terminal for the illumination color “L”: amber, “H”: green (fixed at “H”)
64 LCDCE O Chip enable output to the liquid crystal display driver (IC901)
65 LCDCKO O Serial data transfer clock signal output to the liquid crystal display driver (IC901)
66 LCDSO O Serial data output to the liquid crystal display driver (IC901)
67 LCDINH O Blank indicate control signal output to the liquid crystal display driver (IC901)
“L”: no display
68 UNICKI I Serial data reading clock signal input terminal Not used
69 UNISO O Serial data output terminal Not used (open)
70 UNISI I Serial data input terminal Not used (fixed at “L”)
71 UNICKO O Serial data transfer clock signal output terminal Not used (open)
Input of FM stereo detection signal from FM/AM tuner unit (TU1), and output of forced
monaural control signal to FM/AM tuner unit (TU1) (Commonly used for stereo display input
and forced monaural output)
FM stereo detection at input of “L”, forced monaural at output of “L”
Dolby control in/out terminal
At initial mode: valid/invalid selection input of dolby function (“L” input: valid)
At normal mode: dolby on/off control signal output (“H” output : dolby on)
Not used this function in this set (fixed at “H”)
METAL control in/out terminal
At initial mode: auto/manual mode selection input of METAL function “L”: manual mode
At manual mode: METAL on/off control signal output terminal (“H” output: METAL on)
At auto mode: input at MTLIN (pin %ª)
Not used this function in this set (fixed at “H”)
Power supply on/off control signal output terminal at the illumination and liquid crystal display
driver (IC901) “H”: power on
At power select switch (S501) on mode: “H” output at the accessory on
At power select switch (S501) off mode: “H” output at the power on

– 19 –
Pin No. Pin Name I/O Function
72 BUSON O Bus on/off control signal output terminal “L”: bus on Not used (pull up)
73 SYSRST O Reset signal output terminal “L”: reset Not used (pull up)
74 VREG O CPU regulator output terminal Connected to capacitor
75 GND — Ground terminal
76 X OUT O Main system clock output terminal (4.5 MHz)
77 X IN I Main system clock input terminal (4.5 MHz)
78 CE I CPU chip enable signal input (fixed at “H”)
79 VDD1 — Power supply terminal (+5V)
80 RESET I System reset signal input from the reset signal generator (IC551) and reset switch (S551)
“L”: reset “L” is input for several 100 msec after power on, then it changes to “H”
*1 loading/tape operation motor control
MODE
TERMINAL
LM LOD (pin 8) “H” “L” “H” “L”
LM EJ (pin 9) “H” “H” “L” “L”
STOP LOADING/
FORWARD EJECT/ REVERSE BRAKE

– 20 –
6-2. NOTE FOR PRINTED WIRING BOARDS AND SCHEMATIC DIAGRAMS
Note on Schematic Diagram:
• All capacitors are in µF unless otherwise noted. pF: µµF
50 WV or less are not indicated except for electrolytics
and tantalums.
• All resistors are in Ωand 1/4W or less unless otherwise
specified.
•¢: internal component.
•C: panel designation.
•U: B+ Line.
• Powervoltageisdc14.4V and fed with regulateddcpower
supply from ACC and BATT cords.
• Voltages and waveforms are dc with respect to ground
under no-signal (detuned) conditions.
no mark : FM
( ) : AM (MW)
〈〈 〉〉 :TAPE PLAYBACK
∗: Impossible to measure
• Voltages are takenwithaVOM(Inputimpedance 10 MΩ).
Voltage variations may be noted due to normal produc-
tion tolerances.
• Waveforms are taken with a oscilloscope.
Voltage variations may be noted due to normal produc-
tion tolerances.
• Circled numbers refer to waveforms.
• Signal path.
F: FM
f: AM (MW)
E:TAPE PLAYBACK
Note on PrintedWiring Board:
•X: parts extracted from the component side.
•¢: internal component.
•b: Pattern from the side which enables seeing.
(The other layers' patterns are not indicated.)
Caution:
Pattern face side: Partsonthe pattern faceside seenfrom
(Conductor Side) the pattern face are indicated.
Parts face side: Parts on the parts face side seen from
(Component Side) the parts face are indicated.