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Colour Television – DA100/DW100 Chassis

Sharp Electronics (UK) Ltd

Technical Support

September 99

Page 14

The purpose of this circuit is to maintain the luminance level as the electron spot moves across the
CRT face.

The distance that the electron beam travels from the electron gun to the CRT face at the outer edges
of the CRT is greater than the distance from the electron gun to the centre of the CRT face. This
distance is emphasised more on 16:9 CRT’s than 4:3 CRT’s with deflection angles of 110°

 This result in the intensity of the electron spot varying as it travels across the CRT face. To overcome
this a coil is placed around the CRT neck, close to the gun assembly. The purpose of this coil is to
increase/decrease the speed, the spot travels across the CRT face, therefore, maintaining luminance
transitions.

The signal that is used to control this circuit is derived from IC801 pin 34 and the amount of correction
can be adjusted by the end user via the picture menu.

Q5410

R5431
390

R5433
100

Q5411

Q5412

R5432
33

R5434
1k

R5435
220

Q5406

Q5405

R5412
47

R5413
10

C5408
68nF

R5414
10

C5409
68nF

R5410
0

R5415
82

R5416
3k3

R5418
3k3

R5419
82

R5411
0

R5421
3R3

Q5408

Q5407

R5423
3R3

R5417
0

+5v

140v

+12v

R5425
470

IC801
pin 34

SVM Coils

Colour Television – DA100/DW100 Chassis

Sharp Electronics (UK) Ltd

Technical Support

September 99

Page 15

As in previous chassis a transformer-less driver circuit has been used, with the driver stage obtaining
it’s run voltage from the fly-back transformer, T601.
At switch on +8v from the power supply is applied to Q603 collector via R605 and Q602 collector via
R628 and R608. At the same time –16v is applied to Q602 emitter via R619. Horizontal drive from
IC801 is applied to the base of Q603, This will cause Q603 to switch, which in turn switches the line
output transistor Q601, producing an e.m.f on pins 6 and 10 of the fly-back transformer T601. The
e.m.f at pin 10 is rectified by D611 to produce the positive run voltage and the e.m.f at pin 6 is
rectified by D610 to produce the negative run voltage.

With this type of driver circuit, it is essential that the circuit is started softly, otherwise transient pulses
can damage the line output transistor. This is achieved by doubling the horizontal drive frequency;
which effectively reduces Q601 on time, until the run voltage has been established.

In addition to producing the EHT, focus, screen voltage and horizontal scan from the fly-back
transformer T601, the +/-13v rails for the field output are produced at pins 5 and 9. D609 rectifies the
e.m.f at pin 9 producing the +13v and D608 rectifies the e.m.f at pin 5 producing the –13v.

Horizontal fly-back pulses (HFB) from pin 1 is fed to IC801 for both timing purposes and safety
(prevents excesses EHT), HFB is also rectified by D610 to produce +25v for vertical fly-back. From
the primary winding (pin 7) the HT is stepped up and rectified by D621 to produce the HT required by
the CRT drive circuit. Finally a negative going voltage is fed from pin 8 to the protection circuit. This
voltage represents the beam current. The greater the beam current (Bright Raster) the greater this
voltage would be in a negative direction. This negative voltage is then fed to the IC1001 pin 95 via
D622 and Q606. Once this voltage has exceeded safe working levels IC1001 pin 95 will go low
switching the CTV to standby.

EHT

East/West Circuit

+8V

-16v

Q601

Line
Drive

D610

Focus

Screen

ABL

HFB

+25v

+13v

-13v

10

1

9

5

6

8

13

+150v
(CRT Base)

+150v

2

7

3

4

F602

F601

D609

D608

D510

R617
22

R624
5R6

D604

D603

C601
12nF

C610
27nF

L609

R612
22

C607
330

R619
560

R642
470

R601
3k9

Q602

Q603

R605
470

R607
12k

R628
1k

R608
1k

L606

D611

R623
1

R617
22

D621

Colour Television – DA100/DW100 Chassis

Sharp Electronics (UK) Ltd

Technical Support

September 99

Page 16

In addition to the normal function of an East West correction circuit used with 4:3, 110° CRT, with a
wide screen CTV correction has to be allowed for the different types of scanning modes.

16:9 CTV generally has three scanning modes, 4:3, 14:9 and 16:9, additionally the 16:9 scanning
modes has three variants, Full, Panama 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 line
linearity is not constant across the screen. Panama 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.

IC503 is a switching amplifier with integrated line pulses being fed to one input from the line driver
circuit via Q501 and an East West parabolic signal from IC801 to the other input. This will produce a
PWM signal running at line frequency and the width of the pulses will be determine by the East West
parabolic signal.

This signal is then passed a driver circuit (Q506, class ‘d’ biased), low passed filtered (L603, C610) 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 of L604 is connected to ground with the centre tap connected to
the line linearity circuit. Therefore the line linearity can now be adjusted by the East West Parabolic
signal.

Q601 (c)

Scan Coils

+5v

Diode Modulator

L604

RA611
3k3

L605

C619
2.2

C620
2.2

C613
560nF

D613

R613
2k2

L603

C611
1

D503

R610
1

C518
10pF

Q506

R525
10k

R524
1k

R527
1k

+

-

EW Drive

Line
Drive

+150v

+5v

D506

R519
100k

Q501

C514
47nF

R525
5k6

R555
100k

R556
10k

IC503

Colour Television – DA100/DW100 Chassis

Sharp Electronics (UK) Ltd

Technical Support

September 99

Page 17

The microprocessor (CPU) is at the hart of this CTV, communicating with all other area via various
data buses. Similar to the CS, CA10 and CW100 chassis this CPU is not operating during standby,
therefore contained in the primary side of the power supply there is a slave processor. This slave
processor has a volatile memory, therefore each time power is applied to this CTV the switch mode
powers supply has to start enabling the slave processor program to be downloaded from the OTProm
before switching to standby.

Communication between the CPU and the OTProm (one time programmable read

only memory). This device contains the software (operating system)

There are two I

2

C buses, I

2

C(2) communicates between the NVM’s (eeprom), these

devices contains data relating to all adjustments, whether it is an end user
adjustment, service adjustment or an automatic setting performed by the CPU. I

2

C(1)

provides serial data communications between the CPU and Tuner, Video Processor,
Multi Sound Processor and the Dolby Processor (if fitted).

Data communication between CPU and the teletext processor (MegaText)

Data bus to the slave processor an a data us from the slave processor.

Main system reset, this will operate each time the main switch mode powers supply
starts. Reset is a state change from low to high generated by IC1005.

IC801 reset (low). If IC801 is not reset then the line oscillator will not function. This will
only occur after reset in.

Resets all other areas of this CTV, this will only occur after reset out (1). Teletext
reset is inverted.

If the CPU pin 96 goes low the CTV will switch to standby. This is trigged by one of
the audio output stages or excessive beam current.

Dolby
Processor

Video/Sync
Processor

Tuner

Multi-Sound
Processor

I2C Bus (2)

I2S Bus 

NVM
(eeprom)

NVM
(eeprom)

I2C Bus (1)

Slave
Processor

MegaText

M3 Bus

IC1001
(CPU)

OTP

Main Reset

Reset out (1)
Reset out (2)
AV Link Data

AV Link Clock

AFT-1
AFT-2

IF

IC2028

Protection

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