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Performance Verification
1780R-Series Service Manual
4–65
e. Turn the Precision Measurement control so that the waveform blanking
level is aligned parallel with the CRT graticule baseline (0 IRE for
NTSC; 0.3 V for PAL). The electronic graticule horizontal line will also
be parallel with its nearest CRT graticule line.
f. Turn the Precision Measurement control each direction.
g. Check that the horizontal line, vertical line, and waveform will rotate
equal to or greater than ±1_ from their original position.
h. Turn the Precision Measurement control so that the waveform blanking
level is aligned parallel with the CRT graticule baseline.
i. Check that the electronic graticule lines on the Vectorscope CRT are
straight within ±1_. The electronic graticule lines should be parallel with
the X and Y axis within ±1_.
j. Press the CALIBRATE button to exit the menu and TRACE ROTATION
mode.
k. Disconnect the Color Bar and Black Burst signals from the instrument.
58. Check Return Loss
Requirement: CH A, B1, B2, or B3: >40 dB to 5 MHz. AUX IN, AUX OUT,
or PIX MON OUT (Instrument On only): >34 dB to 5 MHz. EXT REF:
>46 dB to 5 MHz.
a. Connect the output signal from the leveled sine wave generator, through
a 50 WĆto 75 W minimum loss attenuator, to the input connector of the
Return Loss Bridge.
b. Connect the output of the Bridge to the test oscilloscope Differential
Comparator (7A13) inputs. Check that the Red terminator is removed
from the Unknown arm of the Bridge and the Green terminator is
connected to the Reference arm. See Figure 4–13a. Set the test oscillo-
scope for differential mode of operation. Check that the Differential
Comparator + and –Input Coupling switches are set to AC.
c. Set the generator output frequency to 50 kHz and the amplitude to
500 mV p-p as displayed on the test oscilloscope CRT.
d. Change the generator output frequency to 5 MHz. Connect the Red
terminator to the Unknown arm, set the 7A13 for 1 mV/Div, and balance
the bridge. See Figure 4–13b.