akira 14LA/ANZ, Руководство по обслуживанию

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Model No.: 14LAANZACDC
Version: 1.0
f) Vertical divider
The horizontal frequency oscillation pulse from the horizontal scan count divider is
sent to the vertical count divider. Meanwhile the vertical sync signal from the
vertical sync separator (frequency separator) is also sent to the vertical count divider.
Controlled by the vertical sync pulse, the circuit counts horizontal frequency pulses
and identifies and correct vertical frequency, all of which are controlled by the CPU
through the I
2
C bus. The vertical frequency is shifted to the Capture, Identification
or Locking mode by the CPU.
Capture mode: The vertical sync count divider enters the wide-range count
comparison mode, in which the CPU provides a wide-range count comparison value,
i.e. when vertical frequency of the received signal changes within a wide range, the
count circuit can always pause counting and enters another mode for counting and
comparing.
Identification mode: Once the count circuit pauses counting in the Capture mode,
the CPU provides a relatively narrow-range of count comparison value and the
count divider recounts and re-compares until the comparison is finished to enter the
Locking mode.
Locking mode: After identification, the CPU provides a narrower-range of count
comparison value. Only when vertical frequency of the received signal changes
within a very narrow range, can the operation mode be changed and enter the wide
hold range, ensuring the generated vertical drive pulse strict with the vertical sync
pulse.
g) Vertical sawtooth generator and vertical output circuit
The vertical frequency pulse output from the vertical count divider is sent to the
sawtooth generator to develop a sawtooth with corresponding vertical frequency,
which is output from LA76818A’s Pin23 to the vertical output circuit. To get stable
amplitude of the locked vertical frequency sawtooth signal, an auto level limiter
(ALC) is also integrated in LA76818A to control amplitude of the output sawtooth.
Externally connect the ALC’s filtering component to Pin24 of LA76818A. The
chassis’ vertical output circuit consist of LA78040.
The vertical frequency sawtooth from LA76818A’s Pin23 is DC coupled by R451 to
LA78040’s Pin1 to be amplified by the internal differential amplifier. Pin7 is an
in-phase input terminal of the differential amplifier. Externally connected R453 and
R454 are DC bias resistors, and C454 is a filtering capacitor. In the chassis, the
in-phase input of the differentiate amplifier is fixed to reference potential of the DC