Sharp 28JF-73H Service Manual ▷ View online
50Hz Widescreen Colour Television – GA20 Chassis
Sharp Electronics (UK) Ltd
Technical Support
Issued June 02
Page 10
Vertical Driver
The STV9380 is a vertical deflection circuit operating in class D. Class D is a modulation method
where the output transistors work in switching mode at high frequency. The outputted square wave
signal is restored to an analogue signal by an external low pass filter. This method has a low power
dissipation comparatively to traditional amplifiers operating in class AB, eliminating the need of a
heat-sink and makes the device environmentally friendly due to it high efficiency.
Except for the output stage of this device which uses the class D modulation, the circuit operation is
similar to the one of a traditional linear vertical amplifier. A reference signal (sawtooth) has to be
applied to the circuit which can accept a differential or single ended signal. This sawtooth is amplified
and applied as a current to the deflection yoke. This current is measured by means of a low value
resistor (R523). The resulting voltage is used as a feed-back signal to guarantee the conformity of the
yoke current with the reference input signal.
The overvoltage necessary for a fast retrace is obtained with a capacitor (C513) charged by the
supply voltage. At the flyback moment this capacitor is connected in series with the output stage
power supply. This method avoids the need of an additional power supply for the flyback period
C514
470pF
R520
10k
C515
470pF
C516
0.1uF
IC502
SY9380
+v
cc
ea
ou
t
-vc
c
c
-vc
c
c
-vc
c
c
-v
cc
-vc
c
c
-vc
c
c
ou
t
cf
lb
+
cf
lb
-
bo
ot
vre
g
g
Fe
ed
ed
Ca
p
p
Fr
eq
in
+
in
-
gn
d
-vc
c
c
11
20
12
13
14
16 15
17
18
19
1
10
9
8
7
6
5
4
3
2
C517
0.22uF
C513
100uF
R522
1k
D1005
c4v7
+14v
-14v
-14v
L504
C519
560pF
Vertical
Scan Coils
Vprot
Vertical Drive
From IC1001
+v
cc
R519
68k
C521
100pF
R524
150
R525
220
R518
6k8
R523
0R56
0R56
50Hz Widescreen Colour Television – GA20 Chassis
Sharp Electronics (UK) Ltd
Technical Support
Issued June 02
Page 11
Pin Number
Name
Function
1 -V
CC
Negative
supply
2 -V
CC
Negative
supply
3 -V
CC
Negative
supply
4 OUT
PWM
Output
5 CFLY+
Flyback
capacitor
6 CFLY-
Flyback
capacitor
7 BOOT
Bootstrap
capacitor
8
VREG
Internal voltage regulator
9 FEEDCAP Feed-back
integrating
capacitor
10
FREQ
Frequency setting resistor and capacitor
11 GND
Ground
12
IN-
Error amplifier inverting input
13
IN+
Error amplifier non-inverting input
14
EA out
Error amplifier output
15 +V
CC
Positive
supply
16 +V
CC
Positive
supply
17 -V
cc
Negative
supply
18 -V
CC
Negative
supply
19 -V
CC
Negative
supply
20 -V
CC
Negative
supply
50Hz Widescreen Colour Television – GA20 Chassis
Sharp Electronics (UK) Ltd
Technical Support
Issued June 02
Page 12
Audio Output
TDA7480 is a 10W class ‘D’ audio amplifier; it operates on a dual supply or +/- 16v d.c. which is
derived from the switch mode power supply
Pin 12 has three levels, <1.8v d.c. The device is in standby mode (No output)
>1.8v d.c. and <3.8v .d.c The output is attenuated by 80dbs (This feature is
not used)
>3.8v d.c. The device is operating normally
not used)
>3.8v d.c. The device is operating normally
At switch on pin 12 is held low by the mute circuit, preventing any audio output until supply has been
established. Once supply has been established and the operating system is ready for audio to be
produced pin 12 will rise to < 3.8v d.c. The internal oscillator (external timing components at pin 9) will
start, producing a PWM signal at pin 4. This PWM signal has a frequency which is equal to the
internal oscillator plus the frequency of the input signal i.e. if the oscillator frequency = 200,000 kHz
and the input signal = 5,000 kHz, the PWM frequency = 205,000 kHz. The mark space ratio of this
PWM represents the amplitude of the signal at pin 11
R1302
12k
C1301
100pF
100pF
C1306
4700pF
IC1301
TDA7480
+v
cc
cc
-v
cc
-v
cc
-v
cc
-v
cc
-v
cc
-v
cc
ou
t
bo
ot
Os
c
c
Fr
eq
in
St
an
db
y/M
ute
-v
cc
11
20
12
13
14
16 15
17
18
19
1
10
9
8
7
6
5
4
3
2
C1304
0.1uF
+16v
-16v
Power On Mute
+v
cc
cc
Audio Input
C1313
0.47uF
Gn
d
d
C1305
560pF
560pF
C1307
0.47uF
R1306
150R
R1302
100k
L1301
Protection
Loudspeaker
C1313
0.47uF
R1307
27k
R1316
27K
Q1305
R1317
22K
Left Channel
IC1302 pin12
LED 5v
Right Channel
LOW
PASS
FILTER
L1301 and C1307 (Right Channel) L1306 and C1326 (Left Channel) forms a low pass filter for
conversion of the PWM signal into an analogue signal to drive the loudspeaker. A proportion of this
drive signal is fed into an averaging circuit via R1302 (Right Channel) and R1313 (Left Channel) as a
protection signal
50Hz Widescreen Colour Television – GA20 Chassis
Sharp Electronics (UK) Ltd
Technical Support
Issued June 02
Page 13
P
ROTECTION
This CTV is design to switch to standby is fault is detected within the audio output stages. This is
achieved by removing the voltage from IC1001 pin 63, normally IC1001 pin 63 is tied to the +5stby
supply via R1033 and L1006. An averaging circuit comprising of C1323, R1310 and R1311 is used to
sample the audio signal at the loudspeakers. Under normal conditions this average will equal zero
volts. However, with a fault condition the average will move in either a positive or negative direction.
This is detected by Q1302, Q1303 and Q1304.
Q1301
D1301
Q1303
Q1302
R1312
4k7
C1323
1µF
R1311
10k
R1310
10k
R1313
100k
R1312
100k
5v
Standby
-16v
Left
Right
If the average moves in a positive direction then Q1304 turns on removing the voltage from IC1001
pin 63, and for a average which moves in a negative direction then Q1302 and Q1303 turns on,
removing the voltage from IC1001 pin 63.
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