Iiyama Vision Master 405, Руководство по обслуживанию

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4-2. PROTECTION circuit
This circuit is composed of the following protection circuits to prevent a damage to the monitor and X-ray radiation
when the monitor is inoperative.
When the circuit is in the following cases, pin 19 of IC301 turns to 5V and then the horizontal drive signal output
from pin 17 and the variable B control pulse output from pin 14 turn to “LOW” level (0V). It makes the HORIZONTAL
DEFLECTION OUTPUT and the HIGH VOLTAGE OUTPUT circuits stop.
The signal that the X-RAY PROTECTION circuit is activated is sent to IC801 (Microprocessor) from IC301 by I2C-
BUS when pin 19 turns to 5V. IC801 receives the signal and then PS1 signal of pin 27 turns to “HIGH” level (5V) so
that the DC voltages except for the 5V line are turned off.
In case that the PROTECTION circuit is activated and the HORIZONTAL DEFLECTION OUTPUT, HIGH VOLTAGE
OUTPUT and MAIN POWER SUPPLY circuits are turned off, turn OFF and ON the Power Switch to recover.
The PROTECTION circuit operates in the following cases:
Q
+B9 line: The voltage is 180V or more.
R
X-RAY PROTECTION circuit: The high voltage is 29.9kV or more.
S
ARC LIMIT circuit: The beam current is 2.5mA or more.
4-3. HIGH VOLTAGE CONTROL / OUTPUT circuit
The AFC pulse output from the HORIZONTAL DEFLECTION OUTPUT circuit is applied to pin 1 of IC502 and then
a control pulse synchronized with the frequency of the AFC pulse is output from pin 1 of IC502 PCS (primary
control system).
This circuit is to detect a feedback voltage from the FBT (flyback transformer), change the output duty of pin 1 of
IC502, and control the high voltage change due to the brightness changes.
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IC502 Pin 1 output waveform
Q521 Drain waveform
T504 (FBT) Pin 1 waveform