66DW-18H (serv.man3). Revision 1 - Sharp TV Service Manual (repair manual). Page 33

Wide Screen, Colour Television   CW100 Chassis

Sharp Electronics (UK) Ltd

Technical Support

February 99

Page 33

The E / W parabola is generated in IC6110, and applied to pin6 of IC501b. (Non inverting input pin).
Pin 5 of IC501b (inverting pin) has a ramp waveform applied to it from the collector of Q501. This
ramp is generated from the horizontal drive signal (also used for vertical output generation).

The application of the input signal (E/W parabola) and a ramp waveform to the op-amp are all that is
required to perform pulse width modulation proportionate to the input signal. Once this has passed
through the switching amplifier, it the output will appear as varying mark - space ratio square wave
with a swing of 

±

 13V (similar to the vertical stage).

This output is fed via Q605 & Q607. The effect of the East-West circuit is to reduce the amount of
charge available across C610 (Figure 2); thus directly affecting the width of the picture. The fact that
the signal is pulsed rather than analogue will have no effect, the result is the same with an added
advantage of less heat generated by power dissipation in this stage.

In addition due to the size of the CRT fitted to the 76DW18H, the East/West drive signal is also fed to
another switching amplifier (IC503) This signal is used to alter the inductance of the line linearity
circuit and also modulate the focus. Ensuring that the linearity and focus is constant across the width
of the CRT.

Diode Modulator

40V

200V

13V

LOPT pin6

LOPT

ABL

Scan Coils

Line pulses

East/ West Drive

+

-

+

-

Q607

Q605

Q608

Q501

D510

D508

D509
C2V7

D623

D624

D618

D617

D616

D612

D625
C12

D626
C12

D628

DF1

C635

C630

C626

T602

R645

C623

R642

R643

R644

R646

R647

IC503A

R545

R546

C509

C521

R537

R567

R566

IC501A

R502

140V

R538

R541

R627

R639

140V

R610

L602

R651

C606

C631

D601

L604

C619

R624

L605

13V

C607

13V