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Adjustment Procedures
5–42
1780R-Series Service Manual
m. Adjust DC Balance (A7R286) so that the NTSC demodulated burst pulse
overlays the demodulated baseline as displayed on the test oscilloscope.
(For PAL, there are two bursts. Adjust the burst that will null.)
n. Disconnect the test oscilloscope probe from the test point. Disconnect
the Black Burst signal from the 1780R-Series CH A INPUT.
36. Adjust Vector Gains
a. Connect the television test signal generator 5-Step, 40 IRE Modulated
Staircase signal to the 1780R-Series CH A INPUT. Check that the CH A
INPUT is terminated in 75 W and a Black Burst signal is applied to the
EXT REF connector. (For PAL, use 280 mV modulation.)
b. Push the button beneath the Vectorscope CRT.
c. Select LEFT DISPLAY-VECT, REF-EXT-CW and VECTOR GAIN-
VAR on the right front panel. (The vector display will be unlocked.)
d. PRESET Chroma Gain Range (A6R572) to the center of its range.
e. Connect the test oscilloscope 10X probe to TP457 on the Vectorscope
circuit board (A6). Set the test oscilloscope vertical deflection factor to
0.2 V/Div, Input Coupling to AC, BW switch to Full, and sweep rate to
20 ms/Div.
f. Set the 1780R-Series variable VECTOR GAIN control for 800 mV
peak-to-peak display on the test oscilloscope CRT. (Be sure that the test
oscilloscope vertical amplifier BW switch is set to Full.)
g. Remove the 10X probe.
h. Set the HORIZ and VERT POS controls to center the vector center dot
on the Vectorscope CRT.
i. Adjust Vert R-Y Gain (A6R227) and Horiz B-Y Gain (A6R643) so that
the circle is on the compass rose.
NOTE. A6C850 (Quad Phase) may need adjusting to keep the circle symmetrical.
j. Remove the Staircase signal from the CH A INPUT. Connect a 75%
amplitude Color Bar signal to the CH A INPUT. For NTSC only: Check
that the Color Bar generator Setup button is set to 7.5%.
k. Select the 1780R-Series REF-EXT mode and press the PHASE SHIFT
button. Use the Precision Measurement control to place the burst
vector(s) on the graticule reference line(s). 180_ line for NTSC; 135_
and 225_ lines for PAL.