PV154 - 923-03497
3-8
AB - SERVICING
SERVICING
Once the audio is processed the audio stereo amplifier
IC800 TDA7263 (0ISG726300B) delivers the sound
through the speakers.
AUDIO AND VIDEO SWITCHING
FRONT JACK sources available:
• S- Video/ Video Front
REAR JACKS sources available:
• Antenna/Cable1
• Antenna/Cable2
• S-Video/ Video 1
• S-Video/ Video 2
• DVD input (YUV)
• HD Setup BOX (YUV)
• MONITOR OUTPUT (Audio and Video)
RGB VIDEO OUTPUT AMPLIFIER
The video output module drives the RGB cathodes with
video signal from the video drive ICX220M and has one
IC for each color. This circuit includes the filament or
heater G1 and G2 connections and grounds. Special
circuitry senses the cathode current which controls the
cut off gains.
Audio AUX Output stage The AUX or MONITOR OUTPUT audio
output is taken from IC1400, this signal has no processing
and its output is constant.
Below is a simplified block diagram of the AB chassis
video output circuit. The signal is first uncoupled at
the output of the video processor. Then the signal is
derived by the video drive and is applied to the three
transistors Q2205, Q2206, & Q2207 (one per color). After
that RGB signals are injected to the video output board,
it is amplified to the levels required for an acceptable
image on the screen. Each amplifier has a dedicated
section for sensing the cathode current for the AKB
system.
The resistor located at R5125 belongs to the Red color
section. It has the same function of the R5145 of Green
Color section. The three ICs mentioned use the TDA6120Q
from Philips. Each IC came be seen as a operational
amplifier but are configured as inverting amplifiers. The
inverting input is on pin 2 and the non-inverting input
is on pin 4. The Feedback resistor is R5125. It has a
gain peaking network between pin 1 and pin 3. This
network is internally connected to the collectors of the
differential input transistors.
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