Hitachi C28W40TN, Руководство по обслуживанию

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To obtain an accurate biasing of the tube, a continuous cathode calibration circuit is implemented by means of a two point black
level stabilisation circuit. By inserting 2 test levels for each gun and comparing the resulting cathode currents with two different
reference currents the influence of the picture tube parameters like the spread in cut-off voltage can be eliminated.
SIGNAL PATH DESCRIPTION.
The I.F. signal is obtained from SAW filters X200 (vision) and X202 (Sound ) pins 4 & 5 and are fed into pins 2 & 3 vision and 63 &
64 sound of I200. A composite video signal is available at pin 10 from the vision demodulator. I.F. sound out from pin 6. The video is
taken from pin 10 via C304 into pin 12 and out at pin 13. This is the selectable Group Delay via software input output. The
composite video gets taken through buffer and filtering stages where the desired video returns to I200 at pin 14.
The AV switching matrix supports two Scart sockets, phono CVBS and S-VHS inputs. Scart CVBS inputs are at pins 20 (AV1 E301)
and 16 (AV2 E302), CVBS outputs to Scart pins 19 from emitter of Q301 (AV1) and emitter of Q303 (AV2). The RGB input (Digital
models) to I200 from the Digital Terrestrial Tuner (DTT) comes to pins 36-38, from P301 pins 9, 7 and 5, respectively. S-VHS input
is via E300 to pin 23 & 24 of IE02, detection of CVBS input is detected within IE02. For models with progressive scan feature
detection for a Comb filter 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 I200 pins 49, 50 & 51 and go straight into Y
in
U
in
and V
in
(pins 6, 8 and 9 of IE01) for 50Hz
operation, while 100Hz operation, Y, U, V signals are directed to pins 9, 10 & 12 of the double scan module (UQ01).
Other miscellaneous pins such as the sandcastle pin 59 is independent of the sandcastle pulse generated by IE02, they do not drive
each other. The Vertical and Horizontal output pulses generated by I200 drive the double scan module, pins 18 & 19 respectively
(100Hz operation) or the IE02 (50Hz operation) pins 23 & 24. I
2
C control lines are pins 46 & 47, and tuner AGC control voltage is
present at pin 62.
As already previously described Y, U, V signals in either 50Hz/100Hz/Progressive scan mode are sent to pins 26-28 of the TDA
9330 (IE02). Once inside the RGB processor, geometry and synchronisation functions can be implemented before being sent to the
CRT base (pins 40-42 of IE02 & 3-5 of P302) for final video amplification and to the velocity modulation circuit.
The vertical drive output is provided by pin 1 & 2 of IE02 directly to I601 Vertical Output I.C. (pins 11 & 12). Horizontal output is from
pin 8 of IE02 and feeds the base of Q701 Bipolar (50Hz), Q701B MOSFET (100Hz). East-West drive output can be obtained at pin 3
and is driving the gate of the East-West MOSFET Q700.
I
2
C is present at pins 10 & 11 (IE02) and +8V supply rails at pins 7 & 17. Two sets of RGB inputs are available, only one set is used
for the OSD, pins 35-37, the other is for a VGA board which is not fitted.
AUDIO CIRCUIT
The output from the Tuner T1 is fed via a gain and buffer stage formed by Q200 and Q201 to the Saw Filter X202. The saw filter has
two separate characteristics depending on which of the two inputs (on pin 1 and 2 of the Saw Filter) the signal is applied to.
Selection is achieved by the combination of Q204 and Q203. For most standards, pin 1 is selected. However, when an L’ Signal has
been selected , the micro ( I001) instructs I200 via an I2C command to take pin 19 high. When this happens Q204 conducts taking
pin 1low and switching Q203 and D203 off. This means that the collector of Q203 goes high allowing D202 to conduct and hence
the signal to be applied to pin 2. To return to other broadcast standards, pin 19 of I200 is obviously returned to the low condition.
The output of the Saw is applied to pins 63 and 64 of I200. Here the Signal is transformed from the 1st IF (30 – 40 MHz depending
on transmission standard) to the sound IF (5.5 to 6.5 MHz depending on the transmission standard ).
I200 also provides AM demodulation for the L’ and L standards. The demodulated signal appears superimposed on the Sound IF on
pin 5 of I200.
This signal then takes two paths. The first takes it through a Low pass filter formed by R426 and C427 and coupling capacitor C426.
This is then applied to pin 55 of I400 and forms the AM sound Input. The second path takes the signal through a amplifier and buffer
stage formed by Q400 and Q401.
After these stages some high pass filtering is applied by C464 and R477 before the sound IF is applied to pin 60 of I400 via C431.
I400 is The MSP3410D. This IC provides Nicam , FM Mono and FM Stereo Demodulation as well as matrixing of the scart / digital
receiver signals (If Fitted).
The AV1 input is applied on pins 52 and 53, the AV2 input on pins 49 and 50, the AV3 input on pins 46 and 47. The Digital input
(DTT) is applied to pins 43 and 44 (when fitted). In Each case a 100R resistor and 330n capacitor is used.
The Scart outputs on I400 use the following protocol.
Output Signal
Scart Output
Non Digital Models Digital Models
AV1 RF Digital
AV2 Selectable or Auto* Selectable or Auto*
*If auto is selected in the on screen menu’s, AV2 follows the audio of what is being watched the device is I2C Controlled via pins 10
and 11 and receives a reset from the micro at power up on pin 24.The clock is provided by X406 on pins 62 and 63. The device has
three supply rails, 5V Digital (Pin 18), 5v Analogue (Pin 57), and 8v Analogue (Pin 39).