Hitachi CL43WP910TAN, Руководство по обслуживанию

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Synchronisation
.
The sync separator is operated by the Feature Box circuit.
Chroma & Luma Processing .
The IC contains a chrominance bandpass filter , the SECAM cloche and chrominance trap. The filters are calibrated using the tuning frequency and the
crystal frequency of the colour decoder. The luminance output signal which is derived from the incoming CVBS or Y/C signal can be varied in
amplitude by means of a separate gain control .
Colour Decoding .
The colour decoder can decode PAL, NTSC and SECAM signals. The PAL / NTSC decoder contains an alignment free crystal oscillator with 4 separate
pins, a killer circuit and two colour difference demodulators. The 90-degree phase shift for the reference signal is made internally. Because it is possible
to connect 4 different crystals to the colour decoder, all colour standards can be decoded without external switching circuits. Crystals not used must be
left open. The horizontal oscillator is calibrated by means of the crystal frequency of the PLL.
The IC contains an automatic colour limiting circuit which is switchable which prevents over saturation when signals with a high chroma-to-burst ratio
are received. The ACL circuit is designed such that it only reduces the chroma signal and not the burst. This has the advantage that the colour
sensitivity is not affected by this function.
The SECAM decoder contains an auto-calibrating PLL demodulator which has two references, the 4.43MHz sub-carrier frequency which is obtained
from the crystal oscillator which is used to tune the PLL to the desired free running frequency and the bandgap reference to obtain the correct absolute
value of the output signal. The VCO of the PLL is calibrated during each vertical blanking period, when the I.C. is in search or SECAM mode. The
base-band delay line is integrated into the package in order to adjust luminance and chrominance timing.
Signal Path Description .
The I.F. signal is obtained from SAW filters X209 (vision) and X208 (Sound) pins 4 & 5 and are fed into pins 2 & 3 vision and 63 & 64 sound of I201
respectively. A composite video signal is available at pin 10 from the vision demodulator. Either QSS carrier or AM base band sound out from pin 5.
The video is taken from pin 10 via C304 into pin 12 and out at pin 13. This is the selectable Group Delay adjustment via software input output for the
compensation of difference between I&B/G. The composite video gets taken through buffer and sound trap stages where the desired video returns to
I201 at pin 14.
The AV switching matrix supports three Scart sockets, phono (front) CVBS and S-VHS inputs. Scart CVBS inputs are at pins 20 and proceed to pin 16
(Scart1 JY01) and 20 (Scart2, JY02 or Scart3, JY03, Scart2 and Scart3 are selected by external video switch IY01 on terminal PCB, beforehand.) CVBS
outputs to Scart pins 19 from emitter of QY04 (Scart1), emitter of QY01 (Scart2) and emitter of QY03 (Scart3). Scart S-VHS inputs which are via JY02 or
JY03 (switched by IY01) to pin 20 & 21 of I201. Front S-VHS input is via din socket JM02 to pin 23 & 24 of I201. Detection of CVBS input is detected
within I201. Comb filter output has been fitted via Y/C input pins 28 & 29. Colour sub-carrier output for the Comb filter is form pin 30.
Y, U and V signals are taken from I201 pins 49, 50 & 51 and go into pins 9, 10 & 12 of the double scan unit (U301) respectively.
Other miscellaneous pins. I2C control lines are pins 46 & 47, and tuner AGC control voltage is present at pin 62. Sandcastle pin 59 is not in use. HA,
VA out from pins 60 & 61 are also not in use.
Digital Comb Filter
.
The operation of a comb filter is to separate the composite video into luminance and reconstructing the chrominance sub carrier signals using digital
signal processing techniques. The comb filter IC, IC02 has an additional vertical edge enhancement feature.
Composite video input (Pin 6 of connector PN01) and colour sub-carrier (pin 8 of PN01) is to an analogue to digital 8 bit converter where the vertical