Horizontal Deflection Circuit; Horizontal Oscillation Circuit And Horizontal Position Control Circuit - NEC MultiSync FP1370 Service Manual

2-2.HORIZONTAL DEFLECTION CIRCUIT

1) Horizontal oscillation circuit and Horizontal position control circuit

The horizontal oscillation circuit and the horizontal position control circuit are constructed by IC501. The
horizontal oscillation circuit in IC501 is composed of two PLL ( Phase Locked Loop) circuit (PLL1 circuit
and PLL2 circuit).
①PLL1 circuit
MPU (IC801) measures the horizontal frequency of input signal and set the data to the frequency divider
of PLL circuit ( PLL1 and PLL2 ) in IC501. Then IC501 oscillates and controls horizontal position by PLL1
circuit based on MPU data.
The peripheral circuit of pin 13 is filter circuit and decides response characteristic of horizontal frequency.
The voltage at pin 13 is approximately 1 volt DC. The resistors connected to pin 14 and pin 16 (R503 and
R504 ) decide pull-in range of horizontal frequency. Pin 18 is reference voltage terminal of PLL (PLL1 and
PLL ) circuit and outputs 0.92 volt.
IC501
H. sync
Phase Comparator
Approx. 1Vdc
R50J
Filter Circuit
②PLL2 circuit
The PLL2 circuit operates phase locking of fly-back pulse at IC501 pin 27 and duty cycle control of
horizontal drive pulse at IC501 pin 25. The composition of PLL2 circuit is similar to PLL1 circuit. The
peripheral circuit of pin 20 is filter circuit and decides response characteristic of horizontal frequency. The
voltage at pin 20 is approximately 1 volt DC. The resistors connected to pin 17 and pin 19 (R507 and
R508) of horizontal frequency.
IC501 operates phase locking by comparing internal PLL1 circuit output signal with fly-back pulse. The
duty ratio of horizontal drive pulse at IC501 pin 25 is set to approximately 50% by MPU data and this duty
ratio does not depend on horizontal frequency.
1/N Divider
13
Q505
R502
C506
C507
(Fig. 2.3) PLL1 circuit
H. Position/Phase
1/N Divider
VCO
Reference Voltage
16
14
R504
R503
Approx. 1Vdc
8-8
To PLL2
18
0.92Vdc
C509