Deflection Pb Ass'y - Panasonic BT-M1950Y Service Manual

Deflection PB ASS'Y
1. Horizontal oscillator circuit
The horizontal sync signal from the signal PB ASS'Y is supplied via CN001 pin 4 to IC501 pin 9. The signal goes
through the sync separator to the AFC circuit. The flyback pulse waveform is shaped by the IC553 monostable
multivibrator and supplied as the sync signal for comparison to IC501 pin 11.
+12v
FREE RUN
CN00I 0
~ ~---<
+12v
IC553(2/2)
SYSTEM ~C
555
Bo'Hzt60Hz
Q554
SW
Fig. 1-1 H AFC circuit
eMonostable multivibrator operation
ts l•M1950Y
IC553 contains two monostable multivibrators. Both are triggered when input A is Low and at the falling edge of input
B.
The flyback pulse is applied through inverting buffer 0556 to IC553 pin 5. The output pulse width is determined by
R581, R582, C556 and C555. C555 is effective when 0554 is on. 0554 switches on when IC001 detects the
system (NTSC/PAL) and produces a High(NTSC) output. C555 is used to prevent horizontal raster position change
when the system is changed.
One monostable multivibrator output is sent from pin 6 to the other monostable multivibrator input at pin 11. The pulse
width is determined by the time constant of R584 and C557.
eAFC time constant selection
The AFC time constant is normally fixed, but in the BM series, this can be selected by user control for slow, normal
and fast.
These are selected by capacitors and control signals from the MPU. The control signal and mode relationships are
indicated in Table 1-1.
MODE
SKEW 1
SKEW2
Fast High Low
Normal Low
High
Slow Low Low
Table 1-1 AFC and skew signal relationship
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