Model 140A Section 111
Paragraphs 3-1 to 3-14
SECTION 111
OPERATING I NSTRUCTI 0 NS
3-1. INTRODUCTION. 3-8. ASTIGMATISM ADJUSTMENT. To provide
3-2. The Model 140A Oscilloscope is a plug-in uniform focus of the trace over the display area, the
ASTIGMATISM control, a front panel screwdriver
oscilloscope, using a minimum number of functions adjustment, is used in conjunction with the FOCUS
on the main unit. Most of the controls are located on control. For correct adjustment, adjust both FOCUS
the plug-in units, and therefore detailed operating and ASTIGMATISM for sharpest display of signal.
instructions are given in the manuals for the plug-in
units. The Model 140A includes the cathode-ray tube Because different plug-ins will apply different DC
and its associated controls, power supplies, and a potentials to the deflection plates, it will usually be
necessary to readjust ASTIGMATISM whenever plug-
calibrator which is used for vertical-sensitivity and ins are changed.
sweep-time calibration as well as probe compensation.
3-9. REAR PANEL.
3-10. 115/230. This switch, located at the bottom
3-3. CONTROLS AND INDICATORS. of the rear panel, must be set to the nominal line
3-4. FRONT PANEL. voltage before plugging the power cable into the
service outlet.
3-5. Figure 3-1 identifies the front panel controls,
indicators, and terminals, and provides a short 3-11. Z-AXIS INPUT, The Z-AXIS INPUT terminals
description of their functions. and selector switch are located on the rear panel of the
instrument. To externally modulate the trace in-
tensity, set the selector switch to EXT, and apply
modulating signal to Z-AXIS INPUT terminals. The
3-6. BEAM FINDER OPERATION. Frequently the amplitude of modulating pulse required to blank the
CRT trace can be driven off the CRT screen by exces- trace depends upon the level of beam intensity, and
sive DC input levels or by misadjustment of position is about 20 volts positive for average intensities.
or balance controls on the plug-ins. When the BEAM Conversely, a negative pulse can be applied to the
FINDER switch is depressed, the beam is confined Z-AXIS INPUT to intensify the trace. When not
to the screen of the CRT. If the trace is centered with using the terminals, be sure that the ground strap
the position and/or balance control when the BEAM is in place. When the oscilloscope is used with a
FINDER is depressed (see manual for plug-in for dual channel plug-in, the selector switch should be
specific instruction), the trace will remain on screen placed in the INT position. This will connect the
when the BEAM FINDER is released. chopper blanking pulse to the CRT cathode, so that
switching transients will be blanked out when the
NOTE plug-in is being used in the chopped mode of
At high amplifier sensitivities a further slight operation.
adjustment of the balance control may be
necessary. Failure of the BEAM FINDER to
3-12. PLUG-IN UNITS.
bring the trace on screen may generally be
attributed to insufficient intensity or un- 3- 13. INSTALLATION. Insert vertical amplifier
usually high DC signal input. It should also (or other unit desired to produce vertical deflection)
be noted that when single-sweep operation is into the lower compartment, and lock in place.
used with a time base plug-in, the spot at the Insert a time base plug-in (or amplifier) into upper
end of a single sweep will be blanked by compartment, and lock in place. For double-sized
termination of the gate. plug-ins, remove the dividing shield, insert plug-in,
and lock.
NOTE
3-7. TRACE ALIGN ADJUSTMENT. To compensate
for slight manufacturing tolerances and external For proper operation, make sure that the
magnetic disturbances, a front panel screwdriver shield is in place when using standard size
adjustment has been provided to align the trace with plug-ins.
the graticule. Adjust TRACE ALIGN whenever re- 3-14. GAIN. Because of differences in cathode-ray
alignment of the trace seems necessary. A check tube sensitivities, it will usually be necessary to
should be made after moving the instrument to a new readjust plug-in gain when units are interchanged or
operating location. moved from one Model 140A to another.
01638-1 3- 1 |
ACEC
