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High voltage is adjusted by VR105, and stabilized by switching of transistor (Q120) and
control circuit (IC108).
If high voltage increases abnormally in any trouble, the high voltage protection circuit
(IC107) controls high voltage to reduce +B voltage, and stops switching of the horizontal
AFC circuit (IC110) to stop output.
needs to be turned OFF and then ON.
6.4.3.3 Vertical deflection circuit
In the vertical deflection circuit, the vertical oscillation circuit (IC110) and the drive
circuit (IC109) drive the deflection coil to flow vertical deflection current.
6.4.4
VIDEO board (AVB411)
The VIDEO board is consists of the following circuits:
① Amplifiers for each channel of red, green and blue (VIDEO Amp)
② Sync separation circuit
③ NTSC/PAL signal detection circuit
④ Degauss control circuit
6.4.4.1 VIDEO Amp
(1)
Image preamplifier circuit
Image input signal is supplied to the input of image preamplifier (IC300) via the AC
coupling capacitors (C318, C320 and C317).
(2)
Contrast control and image post-amplifier circuit
Varying bias voltage of 24-pin of IC300 controls contrast.
Red (VR304), green (VR305) and blue (VR306) adjust gain of image amplifier channels
for a white balance of image.
Also VR308 adjusts brightness of the contrast center.
IC304 is a final stage of image amplifier to output a signal to the cathode of CRT via
the red (Q303, Q304), green (Q305, Q306) and blue (Q307, Q308).
(3)
Bias control
The red (Q303, Q304), green (Q305, Q306) and blue (Q307, Q308) controls DC bias to
control brightness and white balance of raster.
The red (VR302), green (VR301) and blue (VR300) adjust white balance, while VR303
adjusts brightness of the brightness center.
6.4.4.2 Sync separation circuit
IC305 automatically separates H. SYNC and V. SYNC for following 3 modes of sync
signal input:
① Composite sync
② H /V mixed sync
③ H /V separated sync
IC305 also generates a cramp pulse in the horizontal back porch period to regenerate DC
level of the image circuit.
To release stop of the protection mode, the power
6 - 7
L1E-EA0229
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