Fig. 6-12. Adjustments for trigger circuit on the horizontal display
circuit board assembly.
10. Check External Triggering
a. Equipment setup is given in step 9.
b. Remove the audia signal connection from pin H of the
Vertical Amplifier circuit board and apply the signal to both
the TRIG IN connector on the rear panel of the Type 491
and to a test oscilloscope so the signal amplitude may be
monitored.
c. Set the Audio Signal Generator frequency to 20 Hz and
adjust the output for 0.2 volts. (Monitor the output ampli-
tude with the test oscilloscope.)
d. Change the Type 491 Triggering SOURCE switch to
EXT position and the TIME/DIV switch to .1 s position.
e. Check external triggering. Must trigger with a 20 Hz,
0.2 volt signal applied, with the SLOPE switch in either the
+ or - positions.
f. Increase the Audio Signal Generator frequency to 100
kHz. Readjust the output amplitude to 0.2 volts peak to
peak.
g. Check triggering-Must trigger with a 100 kHz, 0.2 V
signal in the + and - SLOPE positions.
h. Remove the audio signal from the TRIG IN connector.
6-15
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