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1.7 Starter Circuit
When the power switch is turned ON, Q102 is turned ON and a charging current flows into C111 through
R102, R103, Q102, and D105. When the voltage at U101 Pin 7 reaches 16V, the U101 begins to oscillate.
When the U101 begins to oscillate, the currents consumed in U101 and Q101 increased. Therefore, current
is fed from the auxiliary winding (Pin 1 and Pin 2) on primary side of T101.
1.8 Sync Circuit
When the pulses synchronized with the horizontal frequencies (31kHz to 96kHz), are supplied from the
centering choke coil L501 to the sync circuit that is composed of D115, D116, R125, R108, R118, and C119,
the oscillation frequency of the U101 is synchronized with the input horizontal frequency.
1.9 Feedback Circuit
The output of the auxiliary winding on the primary side of T101 Pin 1 is converted into a DC voltage by D110
and C112. This DC voltage is divided by R114 and R115, and is then compared with the reference voltage at
U101 Pin 8. The error from the reference voltage is input to U101 Pin 2 and the output voltage is controlled
until it becomes identical with the reference voltage.
1.10 Snubber Circuit
The snubber circuit consisting of D116, C109, and R122 is intended to reduce the surge voltage that is
generated when Q101 is turned OFF.
1.11 Power Management Function
This is the power saving mode: The power of the 14V line is turned OFF by the MPU (U701), in order to stop
1) When the power switch is kept in the ON position, the MPU detects both the horizontal and vertical sync
signals. If the either the vertical and horizontal sync signals from the PC main unit is no present from the
signal cable, the voltage level at the MPU Pin 29 (PS1) turns HI to cause Q152 to turn ON and Q151 is
turned OFF. This causes the power of the 14V line to be turn OFF and this causes Q503 to turn OFF. In
addition, the -12V power supply fed by U601 from the 14V line is also turns OFF. As a result, operation of
the deflection and the video circuits is suspended.
At that time, the potential at MPU Pin 28 (PS2) turns LOW with a 50% duty, thus making Q155 to turn
ON/OFF. As a result, the heater voltage is lowered and the power consumption is reduced.
2) When the user touches the keyboard of the PC in the OFF mode, the MPU detects the horizontal and
vertical sync signals to reset the monitor.
1.12 Harmonic Coil Changeover Circuit
In order to suppress harmonics generated from equipment, this coil is connected in series with the live side
of the power line. To comply with the world wide specifications for power supplies, the power voltage is
divided by the resistors of R131, R132, and R133 and the resulting voltage is used to cause Q131 and Q132
to turn ON/OFF with the threshold value of ZD131 to drive the coil of RL131. In this fashion, changeover is
conducted to choose a series connection when the source voltage is high or a parallel connection when the
source voltage is low. The source voltage change over is about 170V AC.
the operation of the deflection circuit and the video circuit. At that time,
LED101 changes its color from green to orange.
7-4
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