Sony KDP-51WS550 Training Manual page 42

7. AX-1 Deflection Circuits
The waveforms shown on Figure 7-2 are the typical horizontal circuit signal shapes. The difference between this
set and a conventional set is the horizontal frequency, which is 33.75KHz as opposed to 15.75KHz scan rate in
the conventional set. The 33.75Khz scan rate is considered a high definition horizontal scan rate.
PWM Circuit
(Reference Figure 7-2)
The PWM circuit (Q5201 and IC5201) has two functions. First, it provides a regulated 102Vdc output for the
horizontal output transistor Q5030 collector power supply. Second, it compensates for horizontal pincushion
affect, keeping the picture vertical edges straight.
Regulator
The PWM circuit regulates +135Vdc from the power supply down to +102Vdc. Horizontal pulses from IC5201/
pin 3 drive the gate of Q5201. The pulses are amplified and output to the HOT T5201/pin 3 and out T5201/pin8
to the collector of Q5001 (H-OUT). To control the output voltage, the output at the drain of Q5201 is sampled
(through R5252, R5251, R5221 and R5223) and used to change the pulse width of the H drive pulses. These
changes regulate the output voltage to +102Vdc at T5001/pin 4.
Pincushion Correction
If the PWM output voltage at T5200/pin 3 were changed, the horizontal picture size would vary accordingly. The
EW_PARA parabola signal is first applied to IC5201/pins 6 and 12 and output on IC5201/pin 10 and then applied
back into IC5201/pin 7. The parabola signal at IC5201/pin 7 is compared to the H-Pulse waveform at IC5201/pin
14. This comparison causes the PWM signal at the output IC5201/pin 3 to vary in pulse width. The change in
pulse width causes more or less voltage to be applied to the horizontal output Q5001 collector during the vertical
scan down the CRT. This varying voltage causes a varying current to be applied to the H-DY. Current is
gradually increased as the beam scans down until the current is at its maximum value at the center of the CRT
where the pincushion distortion is the most extreme. The result is a perfect linear (straight line) scan down both
sides of the CRT.
Heater Voltage
The filament voltage is applied when the horizontal oscillator signal produces horizontal sweep and drives the
primary of T5200. The horizontal output transformer T5200/pin 12 outputs 7.7Vdc when power is ON. This
voltage is regulated to 6.1Vdc IC56602 to become the main filament voltage.
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