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Performance Verification
1780R-Series Service Manual
4–29
19. Check Lum/Chroma Gain Ratio
Requirement: X1 Gain Ratio: 1:1 ±1%; X5 Gain Ratio:±0.5%.
a. Connect a modulated 2T Pulse & Bar signal (12.5T NTSC, 10T PAL)
from a Television Test Signal Generator through a 75 W feed-through
terminator to the 1780R-Series CH A INPUT connector.
b. Set the 1780R-Series controls as follows: INPUT–CH A, WFM
HORIZONTAL ONE–LINE, and CONFIGURE–Off. Check that
REF–EXT is selected.
c. Use the VERT and HORIZ POS controls to position the waveform
blanking level to the graticule baseline (0 IRE for NTSC; 0.3 V for
PAL).
d. Check that the bottom of the modulated bar is equal to or less than
7.1 mV or 1.0 IRE for NTSC (7.0 mV for PAL) from the graticule
baseline.
e. Set the front-panel WAVEFORM GAIN to X5.
f. Repeat part c. of this step.
g. Check that the bottom of the modulated bar is equal to or less than
17.9 mV or 2.5 IRE for NTSC (17.5 mV for PAL) from the graticule
baseline.
h. Move the modulated Pulse & Bar signal to each of these INPUT
connectors: CH B1, CH B2, and then to CH B3. Use the appropriate
INPUT button to select each of these inputs.
i. Check Repeat parts c. through g. when checking the channels selected in
part h. of this step.
j. Set the WAVEFORM GAIN–X5 to Off.
k. Disconnect the Pulse & Bar signal from the CH B3 connector.
20. Check Filter Response and Gain
REQUIREMENT Luminance: Less than 3 dB down at 1 MHz. Equal to or
greater than 40 dB down at 3.58 (1780R) or 4.43 (1781R) MHz. Low Pass:
≤14 dB down at 500 kHz.
a. Connect the leveled sine wave generator output, through a 50 W-to-75 W
minimum loss attenuator, to the CH A INPUT connector. Connect a
75 W terminator to this loop-through connector.
b. Select INPUT–CH A and WFM HORIZONTAL–ONE–FIELD mode of
operation.