TM 9-6625-1753-14
C3
(5) A + B mode. For this mode, the operating voltage is removed from the electronic switch, effectively removing it
CHAPTER 3
from the circuit. This allows the two channel outputs to be algebraically summed.
d. Delay Line. In order to get the sweep started, before the signal being displayed gets to the vertical deflection plates,
THEORY OF OPERATION
the signal is picked off for internal triggering, just before it is passed through a delay line. A point on the leading edge of the
signal is used to generate the trigger, which starts the sweep.
e. Vertical Deflection Amplifiers. Since the output of the delay line is comparatively low, it is sent through a series of
Section I. GENERAL THEORY
amplifier stages before being applied to the vertical deflection plates. These amplifier stages (vertical deflection amplifiers)
3-1. Power Supply
produce the necessary power to drive the vertical deflection plates.
The oscilloscope uses four solid-state, low-voltage regulated supplies and one high-voltage regulated supply for its operation
3-2.1. Dual Trace Plug-in 79-02A
a. The low-voltage supplies generate the following voltages: -50, +50, +100, and +200.
a. General. Dual trace plug-in 79-02A (Fig. 4-4.1) consists of two sets of attenuators, two preamplifiers, an electronic
Starting with the -50 volt supply, each supply provides a reference level for the next higher supply, somewhat like adding
switching unit and a common amplifier. One set of attenuators and preamplifiers is provided for channel 1, while the other is
batteries in series. For example, adding the -50 volt supply to the +50 volt supply provides 100 volts.
provided for channel 2. The electronic switching unit allows outputs from channel 1 and/or channel 2, as selected by the
b. The high-voltage supply generates two voltages: +11,200 volts (nominal) and -1350 volts. The high-voltage circuit
MODE selection switch, and the common amplifier further amplifies the selected video. The frequency response of each
consists of a high-voltage oscillator (40 to 60 kc), a high-voltage rectifier (operating as a voltage tripler), and a high-voltage
channel, in the X1 position of the VARIABLE switch, is 0 to 100 MHz in the DC position of the DC-AC-GND switch, and 16 cps
regulator. (The voltage tripler may be vacuum tube rectifiers or solid-state rectifiers depending on the difference among
to 100 MHz in the AC position of the switch (between 3 db points). All the amplifiers in each channel are dc coupled to retain
models covered in paragraph 1-5.) The -135 , volt supply uses a half-wave, solid-state, rectifier to produce the negative
the dc component of the input signal.
voltage.
b. Attenuators. With the VARIABLE control set to CAL, accurate, frequency-compensated attenuators (VOLT/DIV) allow
selection of deflection sensitivities from 0.1-to 20-volts per division in eight steps. All voltage indications obtained must be
3-2. Dual Trace Plug-in 76-021
multiplied by the attenuation of the probe used to determine the true amplitude.
c. Preamplifiers. The preamplifiers are normal push-pull amplifiers. Bias on stages within the preamplifier may be
Each channel of the dual trace plug-in has its own input connection (Fig. 4-2). These are designated channels A and B. Each
equalized to center the trace, or unbalanced to offset the trace, vertically (POSITION control). The gain of the first stages in
channel also has a separate set of switches and controls to provide attenuation or amplification of the signal applied to it. In
either channel may be reduced as desired by adjusting the VARIABLE control. Thus, this control extends the range of the
addition, a common switch permits any one of five signal modes to be displayed.
VOLTS/DIV switch to make continuous control from 0.1-to 50-volts/division available. A NORMAL/INVERT switch makes it
a. Attenuation. The VOLT/DIV selector switch permits the unit to handle a large range of signal voltages. The switch
possible to cross-couple the amplifiers, thus inverting the input signal. Additional sets of amplifiers may be connected by
can be set from 0.005 volts per division to 10 volts per division. However, since the probe provides an additional X10
pulling the VARIABLE switch to the X10 position, thus increasing the gain of each channel by a ratio of 10:1.
attenuation-and since there are six divisions on the graticule screen-the sampled signal can be any value within a range of
d. Switching circuits. A basic timing oscillator (BTO), a channel switching multivibrator, and a switching amplifier
about 0.05 volt (one division) to 600 volts (six divisions).
comprise the switching circuits. The basic timing oscillator may be controlled by a trigger from the delayed sweep plug-in
Measurements can be made with probes other than the X10 probe, in which case one division could equal 0.005 volt.
(ALT mode), or it may free fun at either a 100 kHz or a 1 MHz rate, as selected by an internal switch (CHOP mode). In the
b. Amplification. The individual channel preamplifier takes the single-ended input signal, converts it to push-pull, and
ALT and CHOP modes, the basic timing oscillator controls the channel switching multivibrator. In other modes (CH1, CH2,
amplifies the resulting signal.
and ADDED), the channel switching multivibrator is set to a fixed state (channel 1, channel 2, or off, respectively). The
c. Mode Selection. A MODE selection switch controls the dual-channel output, permitting any one of five modes to be
switching amplifier is controlled by the channel switching multivibrator, and it amplifies the selected signal(s).
displayed. the MODE selection switch operates in conjunction with a conventional bistable multivibrator that functions as an
e. Common amplifier. The common amplifier is a standard push-pull amplifier which amplifies the signal. The output of
electronic switch.
this amplifier is applied through a CRT termination network to the vertical deflection plates of the CRT.
(1) A mode. To display only the signal applied to channel A, the electronic switch is set to one of its two states,
cutting off the channel B output.
3-3. Delaying Sweep Plug-In
(2) B mode. To display only the signal applied to channel B, the electronic switch is set to its opposite ate, cutting off
the channel A output.
a. Triggers.
(3) Alternate mode. In this mode the electronic switch is triggered at the start of each horizontal sweep by a pulse
(1) Normal and delayed triggers. The sweep can be triggered internally, externally, or by the line voltage (60 Hz, 400
that originates in the delaying sweep plug-in. That is, each pulse sets the switch alternately from one state to the other. This
Hz, etc.). These input signals are all processed in the same way, with some point on the leading edge of the signal producing
cuts off the A channel output during one horizontal sweep and cuts off the B channel output during the next sweep. The A
the actual trigger. For normal sweep, an input trigger is needed to produce horizontal deflection.
and B channels are thus alternately switched on and off.
(2) Automatic trigger. For automatic triggering, no input trigger is needed. The automatic triggering circuit gives a
(4) CHOP mode. In the chop mode, the electronic switch is fired by a blanking multivibrator that produces 1- sec
trace on the CRT screen, regardless of whether or not there is an input to the trigger circuit.
pulses at a 60-kc free-running rate. Since the electronic switch is fired at a faster rate than in the alternate mode, individual
segments of each channel's output are displayed alternately.
3-1
