Sony XR-4790 User manual

MICROFILM
SERVICE MANUAL
FM/MW/LW CASSETTE CAR STEREO
AEP Model
UK Model
Model Name Using Similar Mechanism NEW
Tape Transport Mechanism Type MG-25G-136
SPECIFICATIONS
XR-4790/4800
Photo: XR-4800

– 2 –
TABLE OF CONTENTS
1. GENERAL
Location of Controls (XR-4790) .................................... 3
Location of Controls (XR-4800) .................................... 4
Installation....................................................................... 5
Connections ..................................................................... 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. Printed Wiring Boards –Main Section–.......................... 20
6-2. Schematic Diagram –Main Section– ............................. 23
6-3. Printed Wiring Board –Panel Section– (XR-4790)....... 28
6-4. Schematic Diagram –Panel Section– (XR-4790)......... 31
6-5. Printed Wiring Board –Panel Section– (XR-4800)....... 33
6-6. Schematic Diagram –Panel Section– (XR-4800)......... 35
6-7. IC Pin Function Description ........................................... 37
7. EXPLODED VIEWS................................................ 40
8. ELECTRICAL PARTS LIST ............................... 44
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.
(XR-4790)

– 4 –
(XR-4800)

– 5 –

– 6 –

– 7 –

– 8 –
Note: Follow the disassembly procedure in the numerical order given.
SECTION 2
DISASSEMBLY
FRONT PANEL ASS’Y
COVER ASS’Y
1 Push the button
(release).
2 Remove the front panel ass'y
to the direction of the arrow A .
A
2
1
2
1
3
cover ass'y

– 9 –
SUB PANEL, MECHANISM DECK (MG-25G-136)
MAIN BOARD, HEAT SINK
5 screw
(PTT2.6
× 6)
3 connector
(CN351)
2 sub panel
4 flexible flat cable
(CN301)
6 mechanism deck
(MG-25G-136)
1 three screws
(PTT2.6
× 8)
1 three screws
(PTT2.6
× 8)
1 screw (PTT2.6 × 8)
6 heat sink
4 main board
3 two ground point
screws
5 six screws (PTT2.6 × 8)
2 rubber cap (25)
1 two screws
(PTT2.6
× 8)

– 10 –
SECTION 3
ASSEMBLY OF MECHANISM DECK
Note: Follow the assembly procedure in the numerical order given.
HOUSING
ARM (SUCTION)
A part
C part
B part
D part
8 Hold the hanger by
bending the claw.
6 Fit projection on D part.
4 Fit claw on B part.
3 Put the housing
under A part.
5 Fit projection on C part.
1 Install the catch to the hanger.
2 Install the hanger onto
two claws of the housing.
7 Holder the hanger by bending the claw.
hanger
housing
2 Move the arm (suction) in the arrow
direction and fit on profection.
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.
shaft A
shaft B
2
Fit the lever (LDG-B) on
shafts
A and B and
install it.
3 type-E stop ring 2.0
gear (LDG-D)
5 gear (LDG-FT)
6 polyethylene washer
2 tension spring (LD-2)
2 tension spring (LD-1)
gear (LDG-FB)
lever (LDG-A)
hole
hole
4 Align hole in the gear (LDG-D)
with hole the lever (LDG-A)
3 Move the lever (LDG-B)
in the arrow direction.
1

– 12 –
GUIDE (C)
2 guide (C)
1 three claws

– 13 –
SECTION 4
MECHANICAL ADJUSTMENTS SECTION 5
ELECTRICAL ADJUSTMENTS
1. Clean the following parts with a denatured-alcohol-moistened
swab:playback head pinch roller
rubber belt capstan
idlers
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 Torqu 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)
•TapeTension Measurement
Mode Torqu Meter Meter Reading
Forward CQ-102C 30 - 65 g•cm
(0.42 - 0.90 oz•inch)
Forward CQ-102C 0.5 - 4.5g•cm
Back Tension (0.01 - 0.06 oz•inch)
Reverse CQ-102RC 30 - 65 g•cm
(0.42 - 0.90 oz•inch)
Reverse CA-102RC 0.5 - 4.5g•cm
Back Tension (0.01 - 0.06 oz•inch)
FF, REW CQ-201B 60 - 200 g•cm
(0.83 - 2.78 oz•inch)
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 (S801) 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 (S801) 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 3,075Hz
Procedure:
1. Put the set into the FWD PB mode.
2. Adjust adjustment resistor for inside capastan motor so that
the reading on the speed checker or frequency counter becomes
in specification.
Specification: Constant speed
+–
test tape
WS-48A
(3 kHz, 0 dB)
speed checker
or
frequency counter
10 k
Ω
set
LINE OUT
Adjustment Location: See page 16.

– 14 –
TUNER SECTION 0 dB=1 µV
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 Focus Adjustment.
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
FM
98.0

SHUF1
FM Noise Focus Adjustment
Setting:
[SOURCE] button: FM
Procedure:
1. Tune the 98.00 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 RF signal
generator
Carrier frequency : 98.00 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
Ω
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.
FM RF signal
generator
Carrier frequency : 98.0 MHz
Output level : 70 dB (3.2 mV)
Mode : stereo
Modulation : main: 1 kHz, 33.75 kHz deviation (45%)
sub: 1 kHz, 33.75 kHz deviation (45%)
19 kHz pilot: 7.5 kHz deviation (10%)
0.01 µ F
set
antenna jack (J1)
+
–
LINE OUT
level meter
10
Ω
L-CH Stereo separation: A-B
R-CH Stereo separation: C-D
The separations of both channels should be equal.
Specification: Separation more than 28dB
Adjustment Location: See page 16.

– 15 –
AM (MW) Auto Scan/Stop Level Adjustment
Makethis adjustmentafter "FMAuto Scan/Stop LevelAdjustment".
Setting:
[SOURCE] and [MODE] button: MW
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
4. Adjust with the volume RV1 on TU1 so that the “MW” indi-
cation 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
Adjustment Location: See page 16.
AM RF signal
generator
Carrier frequency : 999 kHz
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)
MW
INTRO 999

SHUF1
INTRO
999

SHUF1

– 16 –
Adjustment Location:
RV1 AM (MW) Auto Scan/Stop Level Adjustmen
t
RV2 FM Auto Scan/Stop Level Adjustment
RV3 FM Noise Focus Adjustment
RV4 FM Stereo Separation Adjustment
Tape Speed Adjustment
TU1
—SET UPPER VIEW–

– 17 –
SECTION 6
DIAGRAMS
• IC Block Diagrams – MAIN Section –
IC301 CXA2509AQ-T4
+
–
+
–+–
+
–
+–
12345 6 7 8 9 10
20
19
18
17
16
15
14
13
12
11
2122232627282930
31
32
33
34
37
38
39
40
2425
PBFB1
PBRIN1
PBREF1
PBFIN1
35
36
PBGND
VCT
PBFIN2
PBREF2
PBRIN2
PBFB2
PBEQ1
PBOUT1
VCC
TAPEIN1
AUXIN1
MSLPF
LINEOUT1
NC NC
G2FB
G1FB
MSTC
DGND
MSOUT
NC
NC
INSW
TAPESW
MSMODE
DRSW
MSSW NC NC LINEOUT2 DIREF AUXIN2 TAPEIN2 PBEQ2 PBOUT2 GND
F2
120µ/70µ
X1
X1
VCT
+
F1
120µ/70µ24dB
F3
LPF
VCC
DETECT
MS ON/
OFF
FWD/RVS
TAPE EQ
TAPE/AUX
NR BIAS
24dB
MS
MODE
T2
T1
IC361 MM1322XFBE
1
2
3
4
5
6
7
8OUT2
VS
OUT1
GND
IN1
VCC
IN2
GND
CONTROL CIRCUIT
IC401 LC75373ED
+
–
+
–
+
–
+
–+
–
+
–
+
–
+
–
+
–
+
–
+
–
+
–+
–
+
–
+
–
+
–
DECODER LATCH SHIFT
REGISTER CONTROL
–
+
+
–
12 3 45 6 7 8 9 10
20
19
18
17
16
15
14
13
12
11
21
22
2324252627282930313233
34
35
36
37
38
39
40
41
42
43
44
LSELO
L4
L3
L2
L1
VDD
R1
R2
R3
R4
RSELO
RVRIN
RCOM
RT1 RT2 RT3
RTOUT
RSIN
RS1 RS2 RS3
RSOUT
RFIN
RFOUT
RROUT
VSS
CL
DI
CE
VREF
LROUT
LFOUT
LFIN
LSOUT
LS3 LS2 LS1 LSIN LTOUT LT3 LT2 LT1 LCOM LVRIN

– 18 –
IC601 BA3918-V2
+
–
+
–
+
–
+
–
OVER VOLTAGE
PROTECT
REGULATOR
12 3 45 6 7 8 9 10 1211
NC
MODE2 MODE1
STB
VDD
AMP
VCC ANT
COM
AM
FM
GND

– 19 –
4.6 Vp-p
220 ns
• Waveform – MAIN Section –
1IC501 &¶