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4. Contrast adjustment
• Conditions
(1) Signals
Broadcasting system: M/M
Color system: NTSC color bar (white 75%)
(2) Signal level
Input electric field: 70 ± 3 dBµ (terminated with 75Ω resistance), P/S = 10 dB
(3) Others
US IF input (input electric field should be terminated with 75Ω resistance)
Power supply : Vcc1-1 (CP101) = 5.00 ± 0.05 V
• Adjustment
(1) Connect color terminal (CP320) to GND (CP300) so that screen becomes black and white.
(2) Adjust contrast pot VR300 so that the voltage between pedestal level and white level of B signal
(CP740) is 0.80 ± 0.05 [V].
• Caution
(1) Make sure that waveforms are not distorted.
(2) Connect COLOR terminal of Chroma IC (M52042FP) to GND.
(3) Monitor the B output signal with an oscilloscope via a low-pass filter (C = 2700 pF, R = 100 Ω).
• Block diagram
Signal
generator
Stabilizer
L-PCB
IF signal
B output
Vcc1-1
Low-pass filter
— 6 —
Oscilloscope
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