Mitsubishi Electric Diamond Pro 930SB, Service Manual

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7-4
1.7 Power saving
Suspend mode : Every DC voltage operation of the CRT is reduce to 2 Volt.
OFF mode : The color of the power LED101 switches from green to orange.
1) When the power switch is turned ON when there is nothing being entered in the video cable. At that time, if
the video is shifted from the free-run mode to the suspend mode, the transistor Q151 turns OFF and the
operation returns to the OFF mode within a few seconds.
2) As for the sequence of steps that turn the operation to the OFF mode, if the keyboard is not touched for a
given period of time that a preset in advance, the CPU outputs the LOW level signal to the transistor Q152,
then Q151 turns OFF. As a result the power is shut out at that state.
3) When the user touches the keyboard in the OFF mode, the operation is resumed, the video signals
V-SYNC and H-SYNC turn ON the CPU, then the transistor Q151 and Q152 turn ON. As a result the
operation returns to the ON state.
1.8 DC/DC
The DC/DC voltage is DC 27 volts, and since the set-up voltage is variable from 40 volts to 143 volts, it is
variable depending on the horizontal synchronism. The frequency band is variable from 31 kHz to 110 kHz.
The voltage is fed back from the C330.
1) DC/DC is a step-up circuit, and consists mainly of the choke T501, the transistor Q504, the diode D505
and U501.
2) When the PWM controls U501 IC TDA4856, a driving pulse is generated at the gate of the transistor Q504,
and the transistor Q504 turns ON. During the ON cycle, the energy is stored in the choke T501.
The transistor Q504 turns OFF when the driving pulse disappears from the gate of the transistor Q504.
As a result, the voltage at the dot terminal of the winding flows in the positive direction and goes to the
fly-back rectifier. The energy stored in the choke T501 is entered in the T302, passing through the choke
T501, the diode D505 and the capacitor C523.
3) The feedback is detected by the C331 via diode D315, the capacitor C330, the resistor R349, resistor
R350, VR503 and is connected to the U501 pin 5.
This is loop is the regular type one.
4) The frequency of the synchronization signal coming from video H-SYNC is variable from 31 kHz to 110
kHz. The circuit consists of the R517.
5) The soft start circuit consists of the resistor R518, the capacitor C513, the diode D501 and the Q501.