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Performance Verification
4–48
1780R-Series Service Manual
t. Select SINGLE and NOISE REDUCTION–OFF on the Vectorscope
CRT menu. Press the MEASURE button to exit the menu.
u. Leave the 5-Step Staircase signal connected to CH A INPUT.
40. Check Differential Phase
Requirement: Deflection Factor: 5_ dP deflects the trace 50 IRE (NTSC) or
500 mV (PAL) within a tolerance of ±5%. Residual dP: ≤0.1_, last 90% of
trace. Calibrated dP Resolution: 0.05_; Accuracy: ±0.1_ over full 360_,
External Reference ±0.2 burst lock. Range: 360_.
a. Check that a 40 IRE (280 mV for PAL) Modulated 5-Step Staircase test
signal is applied to the CH A INPUT connector.
b. Check that the 1780R-Series controls are set the same as given in part c.
in Step 39 except as follows: Press the MEASURE button to display the
menu and select DIFF PHASE. Check that SINGLE and NOISE
REDUCTION–OFF are selected.
c. Check that VECTOR GAIN–VAR is On. Adjust the variable VECTOR
GAIN control to place the subcarrier vector dot on the compass rose.
d. Use the VERT POS control to position the waveform blanking level to
the graticule baseline (0 IRE for NTSC; 0.3 V for PAL).
e. Turn the Precision Measurement control so that the chroma overlays the
vertical interval.
f. Use the VERT POS control to place the chroma on the graticule
baseline.
g. Press the REFERENCE SET button.
h. Turn the Precision Measurement control so that the chroma line is
positioned to the 50 IRE graticule line for NTSC (0.8 graticule line for
PAL).
i. Check that the PHASE readout on the Vectorscope CRT is between
–4.75_ and –5.25_.
j. Select DOUBLE on the Vectorscope CRT menu.
k. Turn the Precision Measurement control so that the first step location on
the trace overlays.
l. Press the REFERENCE SET button.
m. Adjust the Precision Measurement control so that the fifth step location
on the trace overlays.
n. Check that the PHASE readout on the Vectorscope CRT is 0.10_ or less.