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B-Y matrixing, the output signals are added with the luminance signal in order to generate the internal RGB
signals.
• RGB selector: it is controlled by the FB signal in signal 26 (RGBIN). The external RGB signals are present
in pins 23 (RI), 24 (GI) and 25 (BI). The RGB selector output is fed to then RGB control.
13.7 RGB Control
• Contrast and brightness control: There are I2C bus controlled. These adjustments can be reduced by the
beam current limiter stage. Furthermore, contrast is affected by the Peak Beam Limiter (Q670 and Q671
circuitry). This circuit's output is the PBL signal to microprocessor's pin 11 and must be 5V with a black
pattern on the screen.
• Beam current limiter/vertical guard: The BCLIN (pin 22) input circuit functions as an average beam current
limiter as well as a peak white limiter. The vertical deflection works correctly when there is a pulse level
above 3.7V during the vertical retrace. The vertical guard function can be I2C controlled. The contrast and
brightness reduction begins when BCLIN level is below 3.0V and 2.0V respectively.
• Continuous cathode calibration (AKB): it is divided into two loops: a black level stabilisation and a cathode
drive stabilisation. Each gun of the CRT is stabilised sequentially and independently and a feedback current
flows to the black current input (pin 18 BLKIN) supplied by the RGB amplifier (IC500). In order to change the
cathode levels at the picture tube three I2C bits are available.
• White point adjust and blue stretcher.
13.8 Supply and bandgap decoupling
The IC400 has two supply pins 12 and 37. Both pins must be supplied simultaneously. The nominal supply
voltage is 8V. The pins 14 and 44 must be connected to ground.
The bandgap circuit provides a very stable and temperature independent reference voltage that ensures
optimal performance of the video processor. Short decoupling (pin 9 DECBG) to pin 14 of the external
capacitor is important for stable horizontal drive.
The comb-filter (IC1050) is only performed with a PAL signal. To enhance the image quality its main features
are: cross colour reduction (only at vertical frequencies), cross luminance reduction and improved video
bandwidth.
The input signal is composite video. It comes from the IC400 (pin 38 CVBSO) to the pin 17 (YEXT/CVBS). It is
processed internally and the resultant signals are Luminance (pin 14 Y0) and chrominance (pin 12 C0). These
signals return to the colour decoder in the video processor. The comb-filter is switched on through the I
by writing a bit in the video processor. This one outputs a 4,43MHz signal on the REF0 port superposed to a
high level one.
With SECAM, NTSC or S-VHS signals the comb-filter is disabled. It bypasses the luminance (pin 17 -
YEXT/CVBS- to pin 14 -YO-) and chrominance (pin 10 -CEXT- to pin 12 -CO-) signals. The video processor
outputs a low level on pin 33.
In the models without the comb-filter, the jumpers JO1050 and JO1051 bypass the signals.
14. Audio processor/A3D Surround/Output amplifiers/Sound IF
The audio processor (IC1300) is controlled via I
signal processing).
• The analog part takes: audio input and output switching, A/D and D/A conversion of input/output sound
signals.
• The digital part: demodulates FM (multistandard) and decodes the two carrier signals, controls the sound IF
AGC, demodulates DQPSK (multistandard) and decodes NICAM.
• The DSP section takes: sound controls, sound effects for loudspeakers, mute for loudspeakers and
headphones, beeper (alarm function) and digital audio switching matrix.
The IC1380 produces the Active 3D Surround (A3DS) effect. The models without A3DS effect use the jumpers
JO1381 and JO1382 to bypass the audio signals to the audio amplifier for loudspeakers.
IC300 is the stereo audio amplifier for loudspeakers, it has a variable gain through the resistive dividers
R303/R304 and R305/R306 (for channels L and R respectively). The power driven is approximately 8W rms. at
10% of distortion (each channel). The input pins (1 and 5) are connected to the audio processor (IC1300) or to
the Active 3D Surround in models that have this feature. Pins 10 and 8 are the loudspeakers power outputs
(channels L and R respectively). The microprocessor can mute the audio by setting high the MUTE signal. This
pin is used only at TV set switch-on and off and in case of bad aerial reception. In all other situations the mute
function is performed by the IC1300.
A fixed gain stereo amplifier is used for headphones (IC350). The input pins (7 and 6 for channels L and R)
come from the audio processor headphones outputs. The headphones connector outputs are the pins 1 and 3.
2
C bus. It has 3 main sections: analog, digital and DSP (digital
7
Service Manual MS CE25FN1-E
2
C bus
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