Acer AM501, Service Manual

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6.4 X-RAY protection circuit
The circuit prevents the X-RAY radiation from exceeding the allowable value when the Anode voltage of
CRT rises abnormally. The voltage to be detected is obtained by rectifying the pulse from FBT pin8,
when the voltage is overhigh, the transistor Q507 will turn on, then the horizontal driver signal will be
disable, the horizontal deflection circuit and high voltage generator immediate shout off. X-RAY
protection circuit will be reset when turn the power off, then turn on again.
6.5 Geometric distortion correction circuit
The geometric distortion correction circuit including:
6.5.1 Side pincushion compensation circuit
The parabola waveform comes from Pin 24 of U401, come to the base of Q501. Via C516, the IIC of
U401 control the gain of parabola waveform, the parabola waveform connected to the diode modulator
amplifier (Q501, Q510, Q503), the side pincushion distortion will be compensated.
6.6 Video amplifier circuit
The video signal input via the coaxial cable, and AC couple to the video PRE. AMPLIFIER
U301MM1375. The signal output from pin 14, pin 17, pin 20, connect to the video output amplifier, the
video signal will be amplify about 50 times (contrast MAX.) and coupling to the cathode of CRT, to light
up the screen.
6.7 Digital Controllor
The digital controller including micro processor U2 NT6861, eeprom U3 24C04, peripheral component,
this controller control, horizontal phase, horizontal size, vertical size, vertical position, pincushion,
contrast, brightness and trapezoid.
The micro processors generate a "MUTE" signal while the input timing changed. And send one signal
(PS1) to power control for power saving function.
MICRO-PROCESSOR also generated one SW signal:
H.SYNC frequency SW SW1
f <41k High 0
f >41k Low 1
There are 4 preset mode and 12 user’s mode can be memorized.