CTX CMS-3436 - Horizontal Deflection Circuit Function

3.3 Comparator Circuit
The comparator circuit including 1C304 and its
peripherals follows the criterion listed below to
achieve necessary changes and presettings of
deflection circuit parameters. It is powered with
a precise 16V regulated from 21V to ensure the
Circuit free from fluctuations caused by power
supply. Q305 and Q306 make up the 16V regu-
lator and VR 303 can be adjusted to output exact
16V DC.
A. Horizontal Oscillation Presetting
15 — 26 26 — 38
High Low
Low High
Frequency(KHz)
IC 304 Pin4
(LM339) Pin 13
Pin 3,4
(4066) Pin 1,2
Hold (1) is first set for 26 — 38KHz range, then
set Hold (2) for 15 — 26KHz, in the latter, Hold
(1) is included in the oscillation circuit and should
not be altered when adjusting Hold (2).
Oscillator
B. Horizontal Position Presetting
Graphics | VGA | EGA | CGA | 8514A
1C304
Pin 1 Low | High | High | Low
Pin 2 Low | Low | High| Low
Pin 13 Low ; Low | Low | High
1C306
Pini0,11 Off On On Off
[_———————I3-— OT OOCO.,.e.e-:-_"|
H.
Center
|
(1)
(2)
(3)
(4)
Shorter
ee
Retrace
12
D. Horizontal Linearity Presetting
Graphics VGA | EGA CGA
IC304 Pini; Low | High High
(LM339) Pin2|} Low | Low High
Q309 Off Off On
Q310 Off On On
a
$-Curve C322 C322 C322
Capacitor Alone | //C330 | //C330
Value //C331
3.4 Horizontal Deflection Circuit
1C301(LA7850) performs the signal processing
for both the horizontal and vertical output
stages. The horizontal sync from Q301 is sent
to Pin 1 of C301, and the phase of the sync pulse
is shifted for horizontal position control. The
shifted level is controlled by Resistors connected
to Pin 2, and the duty of the shifted sync pulse is
determined by R308 connected to Pin 3.
Flyback pulse comes to Pin 4 and a sawtooth
waveform is generated to be compared with the
phase of the shifted sync pulse by the AFC
(Automatic Frequency Control) circuit of 1C301.
Control voltage determined by the AFC ciucuit is
output from Pin 7, then fed into Pin 8 through
R310, Pin 8 is the input pin of VCO (Voltage
Control Oscillator), and locks the VCO to be
sychronous with the input sync pulse.
The synchronized VCO output is further shaped
for driving the output stage, drive signal is output
from Pin 12. Voltage setting on Pin 11 deter-
mines the duty cycle of the drive pulse. Pin 13
is the input of the X-Ray protector, once the
Anode voltage is higher than the set threshold,
the sensed voltage will trigger Pin 13 and turn the
SCR on to shut down the drive signal, the
horizontal deflection output stage is thus turned
off to avoid excessive radiation from CRT.
The drive pulse from Pin 12 is sent to transistor
Q302, through T301, drives the horizontal output
transistor Q303 on and off. When Q303 is turned
on, current flows through horizontal deflection
coil and the primary winding of the flyback trans-
former stores energy. When Q303 is turned off,
B+ charges C322 through deflection coil, cur-
rent flows in opposite direction, and the energy
stored in FBT couples to the secondary side,
supplys Anode voltage and the secondary load.
A H-Width coil connected to deflection coil can
be adjusted for suitable width.