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Performance Verification
4–54
1780R-Series Service Manual
o. Turn the Subcarrier dial on the television test signal generator to place
the red vector dot on the 210_ graticule line on the 1780R-Series
Vectorscope CRT. Turn the 1780R-Series Precision Measurement control
to reposition the red vector dot back to the 180_ graticule line.
p. Check Repeat parts j. through o. eleven more times to check the
complete compass rose (in 30_ increments). Check that the PHASE
readout for each 30_ increment is the same, within 0.10_, as the readout
noted in part m. of this step.
q. Push the MEASURE button to exit the menu. Select REF–EXT on the
front panel.
r. Disconnect the subcarrier signal and termination from the EXT CW REF
connectors. Disconnect the Color Bar signal from the CH A INPUT
connector.
48. Check Chroma Bandwidth
Requirement: Upper –3 dB Point: F
SC
+500 kHz, ±100 kHz. Lower –3 dB
Point: F
SC
–500 kHz, ±100 kHz.
a. Connect a BNC T connector to the output of the leveled sine wave
generator. Connect the generator output from the T connector through a
50 W-to-75 W minimum loss attenuator to the 1780R-Series CH A
INPUT connector. Connect a 75 W terminator to this loop-through
connector. Also, connect the generator output from the T connector to a
digital counter to verify the frequencies within ±1 kHz.
b. Check and/or select the following 1780R-Series front-panel control
settings: LEFT DISPLAY–VECT, RIGHT DISPLAY–WFM, INPUT–
CHA, REF–EXT, FILTER–FLAT, and WFM HORIZONTAL ONE–
LINE.
c. Set the generator output frequency to 3.579545 MHz for NTSC
(4.43361875 MHz for PAL). Adjust the generator output amplitude
control until the vector coincides with the compass rose. Leave the
generator amplitude control at this setting when performing parts d.
through i. of this step.
d. Set the generator output frequency to 3.179545 MHz for NTSC
(4.033619 MHz for PAL).
e. Check that the circle displayed on the Vectorscope CRT is larger than the
3 dB marks. See Fig. 4–10.