Calibration— Type 544/RM544
counterclockwise. Return the TRIGGER LEVEL CEN
TERING R225 control to its fully clockwise position
and repeat step (h).
13. Adjust TRIGGER LEVEL CENTERING R225 and
TRIGGER SENS R245— Fine Adjustment— Sweep
Trigger
a. Set the AMPLITUDE CALIBRATOR switch to 50
mVOLTS.
NOTE
A 50-mv peak-to-peak signal is used in this portion
of the procedure as an adjustment aid only and is
not intended to be interpreted as a trigger-ampli
tude specification.
b. Set the SOURCE switch to EXT.
c. Rotate the TRIGGER SENS R245 control counterclock
wise until the displayed waveform disappears. Then
rotate the control slightly clockwise until the wave
form reappears. Do not turn the control any further
clockwise from this point.
d. Rotate the TRIGGER LEVEL CENTERING R225 control
slowly clockwise until the waveform disappears and
then rotate the control counterclockwise until the
waveform reappears. Continue rotating the control
in a counterclockwise direction until the waveform
disappears. Note the amount that the TRIGGER
LEVEL CENTERING R225 control was moved while
obtaining a display.
e. Set the TRIGGER LEVEL CENTERING R225 control in
the center of the range noted in the previous step.
f. Slowly rotate the TRIGGER SENS R245 control coun
terclockwise until the displayed waveform disappears.
Then turn the control slightly clockwise until a point
is reached where the waveform reappears. Do not
turn the control any further clockwise from this point.
g. Repeat steps (d) through (f) to reduce the range of
movement of the TRIGGER LEVEL CENTERING R225
control, noted in step (d). as narrow as possible while
keepinq the waveform displayed. Also the TRIGGER
SENS R245 control must be adjusted to a counter
clockwise point where, as a final result, a display is
barely obtained. That is, the waveform does not
necessarily have to be stable; a flickering display
can also be an indication of optimum results.
NOTE
One fast method for reaching optimum results is to
let the waveform disappear as described in the first
statement of step (f). Then, use the TRIGGER LEVEL
CENTERING R225 control to make the waveform re
appear. Alternate between the two controls (R225
and R245) until optimum adjustment of both con
trols is reached while still displaying a waveform.
14. Adjust INT TRIG DC LEVEL (Internal Trigger DC
Level) R209— Sweep Trigger
a. Set the AMPLITUDE CALIBRATOR switch to .5 VOLTS.
b. Set the SOURCE switch to NORM INT.
c. Adjust the TU-7 Variable control so the displayed
waveform is 5 mm peak-to-peak in amplitude.
d. Using the TU-7 Vertical Position control, center the
display for equal amplitude above and below the
center graticule line.
e. Set the COUPLING switch to DC.
f. Adjust the INT TRIG DC LEVEL R209 control (see Fig.
5-5) to obtain a stable display. (With the SLOPE
switch set to + , the sweep trace should start on the
positive-going rise of the calibrator waveform.)
15. Check Internal Triggering— Sweep Trigger
a. Set the COUPLING switch to AC.
b. Adjust the TU-7 Variable control until the display is
2 mm peak-to-peak in amplitude.
c. Disconnect the jumper clip lead.
d. Adjust the TRIGGERING LEVEL control to obtain a
stable display.
e. Operate the SLOPE switch. Check for stable time-
base triggering on the —slope when the SLOPE
switch is set to — and stable triggering on the +
slope when the SLOPE switch is set to + . If neces
sary, readjust the TRIGGERING LEVEL control to
obtain a stable display when making the check for
each SLOPE switch position.
16. Check TRIGGERING LEVEL Control Zero S e t -
Sweep Trigger
a. Check that the TRIGGERING LEVEL control is set to 0
and the SLOPE switch is set to + .
b. Connect the VOM between the R217/C218/R218
junction and ground.
c. Carefully rotate the TRIGGERING LEVEL control to
obtain a reading of exactly 0 volts on the VOM.
d. If the TRIGGERING LEVEL knob is set properly on the
control shaft, the white dot on the knob should be
directly below the 0 on the front panel. If the white
dot does not point accurately to 0, disconnect the
VOM, loosen the setscrew in the knob, and reposition
the knob.
e. After tightening the knob, set the knob to 0, recon
nect the VOM, and recheck the reading. The VOM
reading should be zero when the TRIGGERING LEVEL
knob is set to 0.
NOTE
A dc-coupled test oscilloscope with a 10X probe can
be used in place of the VOM to perform this step,
if desired. As another method, the white dot on the
TRIGGERING LEVEL knob should point to 0 to obtain
stable triggering when operating the SLOPE switch
as directed in step 15e.
5-7
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