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Adjustment Procedures
5–32
1780R-Series Service Manual
NOTE. Repeat parts v. through y. of this step, as necessary, to obtain the
frequency response described.
z. Adjust the generator frequency and check for a decreased amplitude of
1% to 3% at 15 MHz, and 4%to 7% at 20 MHz. If the amplitudes at
these frequencies are incorrect, then adjust A2R534 slightly counter-
clockwise to increase the rolloff, or clockwise to decrease the rolloff.
aa. Repeat parts k. through y., if necessary, to obtain proper frequency
response.
ab. Disconnect the equipment from the 1780R-Series CH A INPUT. Leave
the PIX MON OUT connector terminated for Steps 21 through 25.
22. Adjust X5 Frequency Response
a. Apply a modulated 2T Pulse & Bar signal from the television test signal
generator, through a 75 W feed-through terminator, to the 1780R-Series
CH A INPUT.
b. Select the following 1780R-Series settings: INPUT-CH A and WFM
HORIZONTAL-ONE-LINE.
c. Use the VERT POS control to move the waveform back porch or
blanking level to the graticule baseline (0 IRE for NTSC; 0.3 V for
PAL).
d. Set the WAVEFORM GAIN to X5 and the WFM HORIZONTAL
MAGNIFIER to 1 ms/DIV.
e. Adjust X5 Flat Resp (A2C422) slightly, if necessary, to obtain a flat
bottom on the modulated bar.
NOTE. A2C422 was previously adjusted in Step 20i.
f. Set the WAVEFORM GAIN-X5 to Off.
g. Disconnect the Pulse & Bar signal from the instrument.
23. Adjust Input Channel Common Mode Rejection
a. Connect the television test signal generator Multiburst signal, through a
75 W feed-through termination and dual-input coupler, to the 1780R-Se-
ries CH A and CH B1 INPUT connectors.
b. Check that the generator multiburst controls are set to obtain a Full
Amplitude, Composite, High Frequency Range, Markers-On, Sweep
mode output.