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Performance Verification
1780R-Series Service Manual
4–19
l. Remove the four terminators used in part b. of this step and the coaxial
cable from the AUX OUT connector to the test oscilloscope.
9. Check Noise Measurements
Requirement: Accuracy: To 56 dB within 1 dB; 60 dB within 2 dB.
a. Connect the VAC to the 1780R-Series CH B1 INPUT connector. Set the
VAC output amplitude to 45.2 mV.
b. Check that DC RESTORER–OFF is selected.
c. Select INPUT–CH B1 on the 1780R-Series front panel. Press the
MEASURE button to On. Select the NOISE (measurement) pad on the
Vectorscope CRT menu. Set the front-panel WAVEFORM GAIN to
VAR–X5.
d. Turn the Precision Measurement control to obtain a S/N 30 dB readout
on the Waveform CRT.
e. Adjust the VAC output amplitude so that the center traces are nulled on
the Waveform CRT display.
f. Check that the VAC readout is between 42.2 mV and 46.5 mV.
g. Turn the Precision Measurement control to obtain a S/N 50 dB readout
on the Waveform CRT.
h. Set the VAC amplitude to 4.5 mV.
i. Adjust the VAC output amplitude so that the center traces are nulled on
the Waveform CRT display.
NOTE. Due to the low amplitude of the display, exact null is difficult to deter-
mine. Use the Precision Measurement increment buttons to check for equal null
deviation above and below 50 dB. Return to 50 dB.
j. Check that the VAC readout is between 4.0 mV and 5.0 mV.
k. Press the MEASURE button to exit the menu. Check that the WAVE-
FORM GAIN–VAR–X5 mode goes to Off.
l. Reset the VAC amplitude to 999.9 mV.
m. Disconnect the VAC from the CH B1 INPUT.
10. Check Input Gain Ratios
Requirement: Ch A Input to Ch B1 Input: 1 to 1 ±0.002 (0.998 to 1.002).
CH B1 to CH B2 or CH B3: 1 to 1 0.±002 (0.998 to 1.002). Auxiliary Video
Input to Ch A Input: 1.5 dB ±0.3 dB. Ch A Input to Auxiliary Video Output: