Sharp 66ES-D7H (serv.man2) Service Manual ▷ View online
DA100 (50Hz) and DA50W Chassis – Repair Notes
Page 29 of 80
Focus Modulation (66cm and 76cm models only)
Due to their larger screen size's, the 66cm and 76cm models employ a focus modulating circuit. This is driven by
the line output signal.
The function of the focus modulator is to ensure that the outer extremes of the CRT face are kept in focus. As
the beam travels to the edges of the shadow mask, it will become distorted due to the increased distance
travelled when compared with the centre.
the line output signal.
The function of the focus modulator is to ensure that the outer extremes of the CRT face are kept in focus. As
the beam travels to the edges of the shadow mask, it will become distorted due to the increased distance
travelled when compared with the centre.
Circuit Operation
The primary winding of T1602 is connected in the earth return of the line scanning coils, before the signal goes
to earth via the S correction capacitor. This signal is then coupled to the bottom end of the focus control
potentiometers. This is the same for both the FW and GF focus modulator circuits.
to earth via the S correction capacitor. This signal is then coupled to the bottom end of the focus control
potentiometers. This is the same for both the FW and GF focus modulator circuits.
Figure 25: GF Focus Modulator Circuit
Figure 26: Picture of the FW Focus Modulator PWB
Sharp Electronics (UK) Limited - May 2003
Revision 3
DA100 (50Hz) and DA50W Chassis – Repair Notes
Page 30 of 80
Figure 27: FW Focus Modulator Circuit
The FW focus modulator circuit is slightly different to the GF circuit due to the type of screen being used. As
it is not a pure flat screen, the curvature of the screen effects the time that the electron beam takes to reach
the screen by a greater amount than with a flat screen. This effects the focus in both the horizontal and
vertical directions. The horizontal picture is compensated by using the technique described above, however the
vertical correction is derived from the east/west output signal.
Sharp Electronics (UK) Limited - May 2003
Revision 3
DA100 (50Hz) and DA50W Chassis – Repair Notes
Page 31 of 80
Faults in the Horizontal Stage
Horizontal Output Transistor Failure
If the negative supply used to turn off the horizontal output transistor is too low, then it will not turn off fully.
This will result in a large voltage across the collector/emitter junction and current being drawn at the same time.
The power generated will have to be dissipated by the transistor itself and therefore it will get very hot.
Eventually it will fail. A cause of this is failure of C607 (low capacity or leaky), causing the negative supply to
fall. Note that it is advisable to change this for a 105
This will result in a large voltage across the collector/emitter junction and current being drawn at the same time.
The power generated will have to be dissipated by the transistor itself and therefore it will get very hot.
Eventually it will fail. A cause of this is failure of C607 (low capacity or leaky), causing the negative supply to
fall. Note that it is advisable to change this for a 105
o
C device if it has not already been done.
For intermittent failure of the horizontal output transistor it is recommended that C607, D610 and D611 be
replaced. Dry joints in the output stage can also cause this problem – the most common areas affected are the
horizontal coil earth return circuit C613, R613 and associated circuitry and the scan coil connector itself.
Sometimes C613 or R613 will go open circuit resulting in no horizontal scan leading to the possibility of the
horizontal output transistor going short or leaky. C613 can also go faulty under load, so it is best to check by
substitution. C528, C632 and C615 are also known to cause the output transistor to fail intermittently.
It has been known for the power supply opto coupler feedback IC, IC705 to cause the HT to rise slowly. This
results in Q601 failing before the avalanche diode goes short circuit.
Note that the horizontal output transistor must be the correct type. Failure to use the correct transistor will
result in erratic operation or premature failure of the device. Use part number Q601 is RH-TX0144BMZZ for
Q601.
replaced. Dry joints in the output stage can also cause this problem – the most common areas affected are the
horizontal coil earth return circuit C613, R613 and associated circuitry and the scan coil connector itself.
Sometimes C613 or R613 will go open circuit resulting in no horizontal scan leading to the possibility of the
horizontal output transistor going short or leaky. C613 can also go faulty under load, so it is best to check by
substitution. C528, C632 and C615 are also known to cause the output transistor to fail intermittently.
It has been known for the power supply opto coupler feedback IC, IC705 to cause the HT to rise slowly. This
results in Q601 failing before the avalanche diode goes short circuit.
Note that the horizontal output transistor must be the correct type. Failure to use the correct transistor will
result in erratic operation or premature failure of the device. Use part number Q601 is RH-TX0144BMZZ for
Q601.
Horizontal Drive Problems
Sometimes it will appear that there is no horizontal drive signal, even though the microprocessor has gone
through the boot sequence. In this situation, it is possible to release the horizontal mute to enable the
horizontal stage to start. There are a number of ways that this can be achieved, one is to short out the
base/emitter junction of Q607, and the other is to temporarily isolate link JL2.
through the boot sequence. In this situation, it is possible to release the horizontal mute to enable the
horizontal stage to start. There are a number of ways that this can be achieved, one is to short out the
base/emitter junction of Q607, and the other is to temporarily isolate link JL2.
Figure 28: Location of Link Wire JL2
Large Picture
If D1601 on the focus modulator PWB (76cm models only), goes leaky or short circuit, the result is an over large
picture due to the EHT dropping to about 20kV.
picture due to the EHT dropping to about 20kV.
Sharp Electronics (UK) Limited - May 2003
Revision 3
DA100 (50Hz) and DA50W Chassis – Repair Notes
Page 32 of 80
East/West Circuit
In addition to the normal function of an east/west correction circuit used with 4:3, 110° CRT, a wide screen
television correction has to be changed for the different types of scanning modes. Wide screen television
generally has three scanning modes, 4:3, 14:9 and 16:9, additionally the 16:9 scanning modes has three variants,
Full, Panorama and Cinema. Full mode is used to stretch a picture which is in 4:3 format and contains fast moving
action (motor racing), therefore, it does not matter if the horizontal linearity is not constant across the screen.
Panorama is similar to full mode but this time the action is slow or even stationary (news programs), therefore,
your eye would pickup on any variation in linearity. To overcome this the linearity in the centre of the screen is
kept constant and the edges of the picture are stretched to fill the screen. Cinema mode is intended for use
with pictures that are in true 16:9 format. When setting the geometry, the television must be put into the FULL
mode.
The east/west circuit is based around transistor Q506. This transistor operates slightly differently to a
conventional east/west output device as it is turned on to increase the horizontal amplitude and not to reduce
the scan. This enables the circuit to work more efficiently and therefore the transistor does not become
excessively hot during operation.
television correction has to be changed for the different types of scanning modes. Wide screen television
generally has three scanning modes, 4:3, 14:9 and 16:9, additionally the 16:9 scanning modes has three variants,
Full, Panorama and Cinema. Full mode is used to stretch a picture which is in 4:3 format and contains fast moving
action (motor racing), therefore, it does not matter if the horizontal linearity is not constant across the screen.
Panorama is similar to full mode but this time the action is slow or even stationary (news programs), therefore,
your eye would pickup on any variation in linearity. To overcome this the linearity in the centre of the screen is
kept constant and the edges of the picture are stretched to fill the screen. Cinema mode is intended for use
with pictures that are in true 16:9 format. When setting the geometry, the television must be put into the FULL
mode.
The east/west circuit is based around transistor Q506. This transistor operates slightly differently to a
conventional east/west output device as it is turned on to increase the horizontal amplitude and not to reduce
the scan. This enables the circuit to work more efficiently and therefore the transistor does not become
excessively hot during operation.
Circuit Operation
Figure 29: East West Circuit
IC503 is a switching amplifier with integrated horizontal pulses being fed to one input from the horizontal driver
circuit via Q501 and an east/west parabolic signal from IC801 to the other input. This will produce a PWM signal
running at horizontal frequency the width of the pulses will be determined by the east/west parabolic signal.
This signal is then passed a driver circuit (Q506, class D biased), low passed filtered (L603, C610 – C610 is part
of the diode modulator circuit) to the diode modulator (D603 and D604). Additionally from L603 the signal is fed
to one end of a centre tap coil (L604) via C611. The other end of L604 is connected to ground with the centre tap
connected to the horizontal linearity circuit. Therefore the horizontal linearity can now be adjusted by the
east/west Parabolic signal.
circuit via Q501 and an east/west parabolic signal from IC801 to the other input. This will produce a PWM signal
running at horizontal frequency the width of the pulses will be determined by the east/west parabolic signal.
This signal is then passed a driver circuit (Q506, class D biased), low passed filtered (L603, C610 – C610 is part
of the diode modulator circuit) to the diode modulator (D603 and D604). Additionally from L603 the signal is fed
to one end of a centre tap coil (L604) via C611. The other end of L604 is connected to ground with the centre tap
connected to the horizontal linearity circuit. Therefore the horizontal linearity can now be adjusted by the
east/west Parabolic signal.
Sharp Electronics (UK) Limited - May 2003
Revision 3
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