TM 9-6625-1753-14
C10) and the DISPLAY LOGIC switch to emitter follower Q8301 (zone A13) in the horizontal deflection amplifier. Here it is
outputs of the paraphase amplifiers before they go to emitter followers Q8305 and Q8306. If the PULL X10 switch is pulled,
amplified in exactly the same way as the internally generated sweep signal (a above).
the 10 to 1 attenuator is switched out of the paraphase amplifier emitter circuit and attenuator R8316, C8304, C8303 (zone
B14), having a ratio of 1 to 1, is switched into the emitter circuit. With the 1 to 1 attenuator in the emitter circuit, the outputs of
the paraphase amplifiers are magnified 10 times before they go to emitter followers Q8305 and Q8306. By pulling the PULL
3-16.
CRT (Fig. 4-5)
X10 switch, you also insert EXP REG variable resistor R8311 in the base circuit of amplifier Q8303. This resistor controls the
The CRT circuit consists primarily of the controls which affect the CRT electron beam.
operating level of the amplifier. You adjust it to prevent the center of the display from being displaced when the PULL X10
switch is pulled out.
a. Beam Intensity. INTENSITY control R2016 determines the amplitude of the negative voltage (approximately 20 volts)
applied to the CRT cathode. By adjusting this control you vary the beam current, resulting in a brighter or dimmer display on
(3) Continuing with our description, assume that the PULL X10 switch is in its normal position (pushed in). After
the CRT screen.
passing through emitter followers Q8305 and Q8306, the push-pull (180 degrees out of phase) outputs of the paraphase
amplifiers go to output amplifiers Q8308, Q8309 and Q8307, Q8311. In the output amplifiers, the signals develop the
b. Focusing. FOCUS control R2014 determines the magnitude of the voltage applied to the focusing electrode. You
necessary amplitudes to drive the horizontal deflection plates. X AMP LVL variable resistor R8339 controls the operating
adjust this control until the second convergence point of the electron beam is at the screen of the CRT. When the FOCUS
level of the output amplifiers. Trimmer capacitors C8316 and C8317 of the frequency compensation network in the output
control is set properly, the CRT display will be sharp.
amplifier stage are adjusted to correct for any frequency distortion of signals (e.g., rise time and flat top of a square wave)
displayed on the CRT screen.
c. Astigmatism. Astigmatism (a defocusing effect) indicates that the electron beam is in focus in the plane of one pair of
deflecting plates, but out of focus in the plane of the other pair. To correct astigmatism, a voltage is applied between the
(4) After they are amplified and inverted in the output stage, the push-pull outputs go to the horizontal deflection
accelerator electrode (pin 9) and either pair of deflection plates in such a way as to focus the beam at the same point in both
plates in the CRT. You'll notice that the outputs of the amplifier are applied to beam position indicators (neon lamps) DS8301
places. ASTIG variable resistor R2022F controls the voltage applied to the astigmatism electrode (pin 11) to focus the beam
and DS8302 before they go to the deflection plates. These lamps indicate the position of the CRT electron beam when the
in both planes simultaneously.
beam is beyond the left or right side of the CRT screen. For example, let's assume the beam is off the screen (right side) and
lamp DS8301 is illuminated. To produce this action, the difference between the output of amplifiers Q8308 and Q8307 and
d. Pattern Correction. Since there may be poor linearity at the extremes of deflections, STROBE PATT CORR variable
the constant 50 volts applied to the lamp exceeds the lamp's firing potential, causing it to illuminate. If the beam is off the
resistor R2009F is provided to correct this fault. By adjusting R2009F, you vary the voltage applied to the pattern adjusting
screen on the other side (left side), the difference between the output of amplifiers Q8309 and Q8311 and the constant 50
electrode (pin 7), which in turn, varies the electrostatic field produced by this electrode. After the electron beam passes
volts causes lamp DS8302 to illuminate. Remember, a lamp will illuminate only when the beam is off the CRT screen. If the
through the deflection plates (vertical and horizontal) it enters the electrostatic field. The STROBE PATT CORR resistor is set
beam is within the display area of the CRT screen, the output of the amplifiers will not exceed the lamps firing potential, and
until the proper linearity is obtained at the extremes of deflection.
both lamps will be extinguished.
e. Beam Rotate. Since the earth's magnetic field may tilt a trace line appearing on the CRT screen, BEAM ROTATE
b. X Amplifier Only.
resistor R2022 and coil L2001 are provided to counteract the influence of the earth's field. Adjusting the BEAM ROTATE
resistor varies the current through coil L2001, located around the neck of the CRT, and changes the strength of the magnetic
(1) If you wish to use an external signal instead of the internally generated sawtooth signal, set the DISPLAY LOGIC
field produced by the coil. When the electron beam enters the magnetic field it is repositioned. You adjust the BEAM
switch to X AMP. After connecting the external sweep source to the EXT TRIG-X AMP connector, the external sweep signal
ROTATE resistor until the trace line no longer tilts.
passes through PULL EXT 10 switch S813 (zone C1), SOURCE switch S810, COUPLING switch S811, and SLOPE switch
S812 to difference amplifier V8101, V8102. With the DISPLAY LOGIC switch at X AMP, tunnel diode CR8101 is switched out
of the amplifier plate circuit, tile short across X AMP ATTEN variable resistor R8111R (zone D6) is removed, and the short
across V8102 plate resistor R8122 is removed; now the difference amplifier becomes the X input amplifier. The X AMP
ATTEN resistor controls the operating level of the X input amplifier and also the amplitude of its output.
(2) After it is amplified, the external sweep signal passes through attenuation network R8125, R8130, C8119 (zone
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