Sharp 66FW-54H Service Manual ▷ View online
DA100 (50Hz) and DA50W Chassis – Repair Notes
Page 37 of 80
Sharp Electronics (UK) Limited - May 2003
Revision 3
Class D Output Stages
Sharp have used class D output stages for a number of years in discrete component form, but now these are
incorporated into specially designed integrated circuit.
These devices are ideal for use with television audio and vertical output stages where high efficiency (low energy
use) is required. A TDA7480 is used for audio and vertical outputs and the TDA7481 to drive the sub-woofer in
the Dolby Pro-Logic versions of the chassis. The following table defines the operation of each pin of the
TDA7480.
incorporated into specially designed integrated circuit.
These devices are ideal for use with television audio and vertical output stages where high efficiency (low energy
use) is required. A TDA7480 is used for audio and vertical outputs and the TDA7481 to drive the sub-woofer in
the Dolby Pro-Logic versions of the chassis. The following table defines the operation of each pin of the
TDA7480.
Pin Name
Function
Nominal
Voltage Pin
1 -
VCC
Negative Supply Voltage
-13.1V
1
2 -
VCC
Negative Supply Voltage
-13.1V
2
3 -
VCC
Negative Supply Voltage
-13.1V
3
4 OUT
PWM
Output
0V
4
5 BOOTDIODE Bootstrap
Diode
Anode
-2.1V
5
6 BOOT
Bootstrap
Capacitor
9.9V
6
7 NC
Not
Connected
0V
7
8
FEEDCAP
Feedback Integrating Capacitor
0V
8
9 FREQUENCY
Frequency
Setting
Resistor
-11.8V
9
10 SGN-GND
Signal
Ground
0V
10
11 IN
Input
0V
11
12 ST-BY-MUTE
Standby/Mute
Control
Pin
5.0V
12
13 NC
Not
Connected
0V
13
14 +
VCC
SIGN
Positive Signal Supply Voltage
14.1V
14
15 VREG
10V Internal Regulator
-2.1V
15
16 +
VCC
POW
Positive Power Supply Voltage
14.1V
16
17 -
VCC
Negative Supply Voltage (De-coupled by 100nF)
-13.1V
17
18 -
VCC
Negative Supply Voltage
-13.1V
18
19 -
VCC
Negative Supply Voltage
-13.1V
19
20 -
VCC
Negative Supply Voltage
-13.1V
20
Note that pins 1, 2, 3, 17, 18, 19 and 20 are all connected together by a large area of print on the bottom of the
PWB. This area is used as a heatsink for the device. It is very important that all these legs are connected when
replacing the device, as premature failure may occur if they are not. It is also worth noting that when correctly
fitted the IC itself does not get hot during operation.
Pins 8 and 9 – Frequency
The external components on these pins will determine the base frequency of the PWM section of this device.
Remember for the audio circuit the frequency will vary from the base frequency by at least the bandwidth of
the audio signal (20kHz). This ensures that no beat signal is produced which could interfere with the main audio
signal itself.
Remember for the audio circuit the frequency will vary from the base frequency by at least the bandwidth of
the audio signal (20kHz). This ensures that no beat signal is produced which could interfere with the main audio
signal itself.
Pin 12 – Standby/Mute Control Pin
The voltage at pin 12 will determine the working condition of this device. A voltage of less than 0.8v will tell the
device to switch to standby (no output), a voltage between 1.8V to 2.5V will result in the output being attenuated
between 60 to 80 dB. For normal operation the voltage at pin 12 should be greater than 2.7V.
device to switch to standby (no output), a voltage between 1.8V to 2.5V will result in the output being attenuated
between 60 to 80 dB. For normal operation the voltage at pin 12 should be greater than 2.7V.
DA100 (50Hz) and DA50W Chassis – Repair Notes
Page 38 of 80
Vertical Stage
Circuit Operation
The operation of the vertical output circuit is similar to the audio with the exception that there is no mute
circuit, although C511 will stop the circuit from operating until the +13V supply, is present.
circuit, although C511 will stop the circuit from operating until the +13V supply, is present.
Figure 35: Vertical Output Amplifier
The PWM signal from pin 4 of the IC, is passed through a low pass filter (L352 and C504) producing a ramp signal
at the field deflection coils. This ramp waveform will vary between +13V when the scan is at the top of the
screen decreasing to –13V when the scan has reached the bottom of the screen. The field scan coils are returned
to ground via Q503. Q503 is turned on during the vertical scan period and turns off during vertical fly-back.
IC502 will produce an error signal. This error signal is fed to the vertical drive input (IC501 pin 11), for the
purpose of linearity and amplitude correction.
at the field deflection coils. This ramp waveform will vary between +13V when the scan is at the top of the
screen decreasing to –13V when the scan has reached the bottom of the screen. The field scan coils are returned
to ground via Q503. Q503 is turned on during the vertical scan period and turns off during vertical fly-back.
IC502 will produce an error signal. This error signal is fed to the vertical drive input (IC501 pin 11), for the
purpose of linearity and amplitude correction.
Vertical Fly-Back
At the point where vertical fly-back is initiated Q503 turns off and Q502 turns on, allowing the +25V supply to
connect to the field scan coils. Since there is –13V on the other side of the scan coils derived from the vertical
drive signal, we effectively have 38V across the field coils, which will force the scan to the top of the screen.
The vertical drive signal that is comes from IC801, pin 31, has a negative going pulse in addition to the normal
ramp waveform. This negative pulse is used to initiate vertical fly-back. This drive signal is applied to the emitter
of Q505 via R508. The potential divider R526 and R514 will fix Q505 base voltage so that it will only turn on
during the period of the negative going pulse. Once Q505 turns on its collector voltage will fall turning on Q507
taking its emitter to ground, which results in:
connect to the field scan coils. Since there is –13V on the other side of the scan coils derived from the vertical
drive signal, we effectively have 38V across the field coils, which will force the scan to the top of the screen.
The vertical drive signal that is comes from IC801, pin 31, has a negative going pulse in addition to the normal
ramp waveform. This negative pulse is used to initiate vertical fly-back. This drive signal is applied to the emitter
of Q505 via R508. The potential divider R526 and R514 will fix Q505 base voltage so that it will only turn on
during the period of the negative going pulse. Once Q505 turns on its collector voltage will fall turning on Q507
taking its emitter to ground, which results in:
Sharp Electronics (UK) Limited - May 2003
Revision 3
DA100 (50Hz) and DA50W Chassis – Repair Notes
Page 39 of 80
Q503 turning off due to the removal of its gate bias.
Q502 turns on because of D507 conducting and pulling its base voltage lower than its emitter.
Figure 36: Vertical Fly-back Circuit
From the junction of Q502 collector and the scan coils the vertical fly-back pulse is applied to IC801 pin 11
(Vprot Signal). This is an indication that the vertical output stage is operational. If IC801 cannot detect the
negative edge of this pulse then IC801 will presume that the vertical stage is not operating correctly and blank
the RGB drive.
(Vprot Signal). This is an indication that the vertical output stage is operational. If IC801 cannot detect the
negative edge of this pulse then IC801 will presume that the vertical stage is not operating correctly and blank
the RGB drive.
Figure 37: Vertical Protection Signal (VPROT - Pin 11 of IC801)
Sharp Electronics (UK) Limited - May 2003
Revision 3
DA100 (50Hz) and DA50W Chassis – Repair Notes
Page 40 of 80
Figure 38: Vertical Scan Coil Waveform - Top of Coil
Figure 39: Vertical Scan Coil Waveform - Bottom of Coil
Sharp Electronics (UK) Limited - May 2003
Revision 3
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