Barco GRAPHICS 1209S, Руководство по обслуживанию

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Date: 10/02/98 R762839
RGB Output/ABL+CRT R762839
15
Technical Description
This pulse is used to inhibit the blanking and to switch Q1 to the reference voltage. This
voltage is formed by R78 and R79 during the measurement pulse and is then +2.4V.
During the leakage measurement is transistor Q16 in conduction and lowers this
reference with R101 to +2.0V. IC10 buffers this voltage and can sink the base current
of Q1.
The leakage current enters the control loop through pin 10 ofJ3/J4 and is converted to
a voltage with R71. This voltage is first amplified with IC9 pins 1, 2 and 3 with a factor
90. The diodes D22 and D23 limit the input levels.
During the leakage measurement the emitter of the transistor Q7 is high and pins 1,
10 of the switch IC4 are closed. The amplified voltage comes on C18 and is compared
with ground by IC9, pins 5, 6 and 7 which adjusts the bottom of R71 until steady state.
This system compensates for leakage currents that might flow out of the cathode.
During the measurement pulse is the level at MP6 high and the switch IC4 pin 3, 4 and
9 is closed. The input reference is now 2.4V at the base of the transistor Q1 and this
should give a cathode current of about 20
µ
s.
The amplified voltage that corresponds to this current comes on capacitor C19 and is
buffered by IC3 pin 5, 6 and 7. The voltage is compared by IC3 pin 1, 2 and 3 with a
reference and adjusts the output DC level at the collector of Q3 trough R30.
During the leakage measurement the input voltage at Q1 is equal to 2V, and the output
voltage should be 185V. This voltage is divided with R68, R69, R70 and P30 to 0V. This
voltage is buffered by IC6 pins 5, 6, 7, and compared by the comparators IC5 with 2
references. The potentiometer P30 is aligned so that the LED D30 is turned off at an
output black level of +185V. The G2 potentiometers can then easily be adjusted (if the
LED D30 turns off, the G2 is at the correct level because the cathode is at 185V black
level.
The Power Supply had to be regulated to guarantee the performance of the VPH08 and
to eliminate variations on the +210V Power Supply. The +200V is divided by R90, R91,
R92 and P3 to 0V and compared with ground by IC6 pins 1, 2 and 3. If the output voltage
is too low, pin 1 goes higher and more current is flowing through Q15, Q13 and Q14
as to raise the output until steady state. The transistor Q12 limits the peak current.
Regulated Power Supply