Horizontal Deflection; Horizontal Scanning - Sony KP-43T70 Training Manual

Horizontal Deflection

Overview
The horizontal deflection circuit has two main functions:
•
Control horizontal scanning of the CRT beams.
•
Along with the flyback transformer create high voltage for the picture
tubes.

Horizontal Scanning

There are 3 circuits used to control Horizontal beam scan:
•
Horizontal Drive
•
Pincushion
•
Centering
Horizontal Drive
When +9V line is applied to the Y/C Jungle IC301 X304 begins to
oscillate. This is a 32fh signal that is used as a reference for the hori-
zontal oscillator inside the Y/C Jungle. When the Y/C Jungle IC confirms
communication with System Control IC001 it begins to output 8vp-
phorizontal drive pulses at pin 35. (See Waveform "A")
These pulses are input to the base of Q501 and then a 90 vp-p signal is
output at the collector and applied to T501 the Horizontal Drive Trans-
former. (See Waveform "B")
"A"
2v
5ms
xv
T501 induces a 12 vp-p signal onto its secondary which is connected to
the base of Q502 Horizontal Output. (See Waveform "C")
Q502 and associated components amplify and waveshape the signal so
that 1000 vp-p spikes are output and applied to the yokes and Flyback
Transformer T504.
Also a sample of this pulse is sent back to the Y/C JungleIC301/36 HP/
Hoff. This pulse is compared to the reference created by X304 for phase
correction of the horizontal oscillator. The HP pulse is also sent to IC001
System Control for OSD positioning and IC802 Wave Generator. (See
Waveform "D")
Pincushion
The purpose of the pincushion circuit is to correct for deflection distor-
tion. This distortion occurs because of the yokes inability to create a
linear beam scan. The result would be a picture bowed at the sides, top
and bottom. We compensate for this problem by using pincushion
correction circuits. Pincushion correction for horizontal scanning in this
"B"
set is described below.
1v
Pincushion correction is achieved by modulating the horizontal scan
50us
current with a vertical parabola. The resulting signal causes the hori-
zontal scan current to be least at the top of the raster, but to gradually
increase to maximum as the beam reaches the vertical center of the
screen. As the beam continues to move towards the bottom of the
screen, the horizontal scan current gradually decreases. The result is a
raster with straight sides.
"C"
1v
5ms
"D"
5v
50us