Iiyama Vision Master Pro 451, Service Manual

Page: 33 / 74

4-7. HIGH VOLTAGE CONTROL / OUTPUT circuit
The AFC pulse output from the HORIZONTAL DEFLECTION OUTPUT (L501 pin 9) applied to pin 4 of IC501
(HV-CONT-IC) and then a control pulse synchronized with the frequency of the AFC pulse is output from pin 1 of
IC501 and operate Q521 (HV-OUT).
For stabilizing high voltage output control, this circuit is to detect a feedback voltage from pin 11 of T501 (FBT) and
feed back to pin 6 of IC501, change the output duty of pin 1 of IC501, and control the high voltage change due to the
brightness changes.
4-8. 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 IC350 (XRAY) turns to 5V and then the horizontal drive pulse
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 IC301 (Main Microprocessor) from IC350 by
I
2 C-BUS when pin 19 turns to 5V. IC301 receives the signal and then PS1 signal of pin 8 of IC104 turns to “LOW”
level and PS2 signal of 15 pin of IC104 turns to “HIGH” so that the MAIN POWER circuit is turned off.
In case that the PROTECTION circuit is activated and the HORIZONTAL DEFLECTION OUTPUT, HIGH VOLTAGE
OUTPUT and MAIN POWER 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 220V or more.
R
X-RAY PROTECTION circuit: The high voltage is 29.0kV or more.
S
ARC LIMIT circuit: The beam current in FBT is 3.0mA or more.
IC501 pin 4 AFC input
(50V/div)
T501 pin 1 output
(200V/div)
Q521 Drain output
(200V/div)
IC501 pin 1 H/V output
(20V/div)
- 28 -