Product specifications

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.
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.
Sharp Electronics (UK) Limited - May 2003
Revision 3