Fig. 6-15. Location of trigger and sweep adjustments.
c. Preset the Sweep Cal R787 to midrange. Adjust the
Sweep Gain R813 (see Fig. 6-15) for 10.5 divisions of sweep
length. Adjust Sweep Cal R787 for 1 marker per division.
Sweep timing must be within ±3% (1.2 minor divisions)
over the center 8 graticule divisions.
TABLE 6-3
14. Check Sweep Timing Accuracy
a. Equipment setup is given in step 13.
b. With the Marker Output signal from the Time-Mark
Generator applied to pin H of the Vertical Amplifier circuit
board, adjust the LEVEL control for a stable triggered trace.
Position the zero timing mark and the start of the trace on
the left graticule line.
c. Check timing accuracy (±3%) at each position of the
TIME/DIV selector. Marker input and Type 491 display for
each position is listed in Table 6-3.
15. Check VARIABLE Control Range
a. Equipment setup is given in step 14
b. Apply 5 ms markers to pin H of the Vertical Amplifier
circuit board assembly. Set the Type 491 TIME/DIV selector
to 1 ms and adjust the Triggering LEVEL control for a stable
display. One 5 ms marker/5 divisions.)
c. Turn the VARIABLE control fully counterclockwise.
d. Check-A minimum of five markers should be displayed
within the 10 division graticule width. Variable control range
2.5:1.
16. Check SAW OUT Signal Amplitude
a. Equipment setup is given in step 12.
b. Connect the
1× probe from the test oscilloscope to
the SAW OUT connector on the rear panel of the Type 491.
Fig. 6-16. Sawtooth waveform and blanking waveform.
6-18
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