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Performance Verification
4–62
1780R-Series Service Manual
NOTE. Perform parts i. through o. of this step only if the internal jumpers for
A6J108 and A6J205 are installed to operate the instrument in the High Gain
mode.
i. Connect the sine wave oscillator to pin 11 and ground pin 9 of the X Y
INPUT connector.
j. Set the sine wave oscillator output frequency to approximately 10 kHz
and adjust its amplitude for a display equal to the diameter of the
graticule compass rose.
k. Set the oscillator frequency to 100 kHz.
l. Check that the display reaches the –3 dB gaps in the horizontal axis or
beyond.
m. Move the sine wave oscillator signal so that it is applied to pin 15.
Connect pin 13 to ground.
n. Repeat parts j. and k. of this step.
o. Check that the display reaches the –3 dB gaps in the horizontal axis or
beyond.
p. Disconnect the sine wave oscillator from the instrument.
q. Disconnect the X Y INPUT connector and Color Bar signal.
56. Check SCH Phase Accuracy
Requirement: Absolute Phase Accuracy: ±5_ phase at 25_C. Acquisition
Time: ≤1 sec. External Reference: 360_. Internal Reference: ±70_. Synchro-
nization: 286 mV for NTSC (300 mV for PAL) sync and burst ±3 dB. Line
Strobe Out occurs on Line 11 (NTSC) or line 7 (PAL).
a. Connect a Color Bar signal from a TEKTRONIX TSG–170A NTSC
Television Generator to the 1780R CH A INPUT connector. Connect a
75 W end-line termination to the remaining CH A INPUT connector.
Connect the generator Black Burst signal to the EXT REF connector.
Check that the EXT REF loop-through connector is terminated into
75 W. (Use a TEKTRONIX TSG-271 PAL Generator for the 1781R.)
b. Select the 1780R-Series LEFT DISPLAY–SCH mode of operation.
Check that REF–EXT is selected.
c. Use the VERT and HORIZ POS controls to position the vector center
dot to the exact center of the vector graticule.
d. Press the PHASE SHIFT button to On. Rotate the Precision Measure-
ment control to place the burst vector(s) to their reference target(s). Press
the PHASE SHIFT button to Off.