Horizontal Drive Circuit; Horizontal Deflection Output Circuit; Horizontal Size Control Circuit - NEC MultiSync FP1350 Service Manual

3) Horizontal Drive Circuit

The horizontal drive system uses what is generally referred to as a flyback system.
The horizontal drive pulse output from IC501 pin 25 switches Q555 on and off.
It is amplified by T551 and switches Q561 (the horizontal output transistor) on and off.
The voltage of C552 for horizontal drive is fixed at 15V.

4) Horizontal Deflection Output Circuit

It corrects the optimum horizontal linearity by using Linear-coil and S correction capacitor to change the
horizontal frequency mode. Horizontal frequency mode is shown in CPU CIRCUIT description section.
The Inductance of Linear-coil (T571) varies with horizontal frequency.

5) Horizontal Size Control Circuit

Horizontal size is controlled by power-supply voltage for a horizontal deflection made using PWM method.
The horizontal size is controlled by two methods. One is H-SIZE which can be adjusted with a user menu,
and the other is H-SIZE MAX which can be adjusted only with a service menu. The horizontal size control
circuit consists of the circuit shown in the following.
• Saw-tooth-wave form generator
• Switching pulse generator
• PWM Chopper
• +B modulation circuit
A saw-tooth wave form is generated inside IC592 . Its frequency is depend on horizontal drive pulse signal
input at pin 8 and its slope is decided by the time constant of R59J and C598. The waveform can be
monitored at pin 3.
Horizontal size control voltage is compared with reference voltage from pin 6 of IC592, output is fed into
pin1 of IC592. On the other hand, horizontal maximum size control voltage is compared with AFC feedback
voltage and then output is fed to a buffer circuit inside IC592 at pin5 and output at pin4 of IC592.
These 2 comparing voltages that are inputted at pin 1 and 13 shall be compared within IC592 as well as
feedback from output voltage of PWM chopper circuit. Output of comparison is the voltage that controls the
duty cycle of square wave that generated from saw-tooth waveform. Square wave is buffered and output at
pin 9 of IC592 to the gate of Q5G1,PWM modulation.
Source voltage (220V) of Q5G1 is converted into horizontal deflection voltage by the duty cycle of the square
wave. This voltage is supplied to a horizontal size modulation circuit consists of Q5A1, R5AC, R5AE, C5A5,
C5A8, and ZD5A1. Transistor Q5A1 modulates chopper DC output voltage from L5G2, C5G3. Self bias voltage
by R5AC and R5AE , and a modulation wave form( E/W parabolic wave form) is applied to a base through
C5A6. A modulation wave form is made in the distortion correction circuit described in below section
IMAGE C519 WAVE
CORNER
BTM BALANCE
MIN.
(Fig.2.8) voltage at C519 and screen image
C519 WAVE
LEFT/RIGHT
TILT
CORNER
TOP BALANCE
OSM MENU
8-11
IMAGE
MAX.