Tektronix 323, Инструкция по эксплуатации

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Circuit Description— Type 323
blanking to occur. Protection from large external blanking
signals is provided by R351 and D351. Signals at the EXT
BLANK connector in excess of approximately + 8 V will
cause D351 to go into conduction, limiting the signal at
D353 to +5.6 V.
When the end of the sweep initiates retrace, Q305 turns
off and D350 goes into conduction. This turns D353 and
Q356 off and the circuit returns to its quiescent condition.
C353, C361, C362 and C364 improve circuit response suf­
ficiently to cause the electron beam to be blanked before
an appreciable amount of retrace occurs.
Residual voltage exists in the high voltage power sup­
ply for a brief period after the Oscilloscope is turned off.
As long as some voltage remains in the +100 V power
supply, it appears on the non-driven unblanking deflection
plate. It is also applied to the base of Q373 through con­
tacts of the POWER switch and R369. This keeps Q373 in
conduction, grounding the driven unblanking deflection plate,
thereby keeping the CRT blanked while the high voltage
power supply discharges and the CRT filament cools.
EXT HORIZ Operation. When EXT HORIZ operation is
selected by the TIME/DIV switch, R340 is connected in par­
allel with R342. The collector of Q326 is connected directly
to the gate by Q311, bypassing timing capacitor C330.
R330 (the timing resistor) becomes disconnected from the
circuit. The parallel combination of R340 and R342 switches
D303 to its high voltage state, turning Q305 on. Unblank­
ing occurs, but removing the timing resistor and short cir­
cuiting the timing capacitor prevent a sweep from being
generated. The intensity should be turned down under this
condition to provide optimum viewing and to conserve op­
erating power, thereby lengthening the operating cycle dur­
ing internal battery powered operation.
HORIZONTAL AMPLIFIER <6>
General
The Horizontal Amplifier accepts a horizontal sweep volt­
age from the Sweep Generator, amplifies it and applies the
resulting push-pull signal to the horizontal deflection plates
of the cathode-ray tube. During EXT HORIZ operation, the
input from the Sweep Generator remains constant, allow­
ing EXT HORIZ input signals to be amplified and applied
to the horizontal deflection plates. The overall gain of the
amplifier is normally about 50 and increases by a factor
of 10 during X 10 HORIZ MAG operation.
Block Diagram Description
Refer to the block diagram on the Horizontal Amplifier
schematic page. The horizontal sweep signal received from
the Sweep Generator passes through a horizontal gain cali­
brating resistor, is amplified by the Output Amplifier and
is then applied to the left deflection plate of the cathode-
ray tube. The Output Amplifier is an operational amplifier
whose feedback circuit is modified when X 1 0 HORIZ MAG
operation is selected.
The signal at the left deflection plate drives the Output
Inverter, which supplies the signal to the right deflection
plate. The Output Inverter is also an operational amplifier
and has a gain of one under all operating conditions.
As the electron beam is moved from left to right across
the face of the cathode-ray tube, the Output Amplifier cir­
cuit current decreases as its voltage output decreases.
Simultaneously, the Output Inverter current increases in step
with its output voltage. During retrace the reverse is true.
The Current Control Circuit exchanges the current between
the two circuits to provide optimum operating efficiency.
The quiescent beam position (and therefore the horizontal
area through which the beam moves) can be selected by
the POSITION control, and it is normally set to cause the
sweep to start at the first marking at the left of the graticule.
During X 10 HORIZ MAG operation, the POSITION control
range permits any 10% of the normal sweep to be presented
as a 10 division sweep.
When EXT HORIZ operation is selected by the TIME/
DIV switch, the Horizontal Amplifier circuit operates exactly
as previously explained, except that the sweep signal from
the Sweep Generator circuit has been replaced by an ex­
ternally applied signal. When the EXT HORIZ VAR control
is fully clockwise, R334B is bypassed. The external hori
zontal gain will decrease to 1/10 its previous value wher
the control is rotated fully counterclockwise.
Output Amplifier and Output Inverter
Refer to the schematic of the Horizontal Amplifier. Sig­
nals from the Sweep Generator cause current flow through
R401 ( X I GAIN) and R402. A very small percentage of this
current passes through the base-emitter junction of Q415,
which causes a current drive signal to be sent to the bases
of Q420 and Q427. This causes an output voltage change
(at the collector of Q427) with a polarity opposite to that
of the signal voltage change applied to R401. The output
voltage causes almost all of the R401, R402 signal current
to flow through R430 and R431 except for the small amount
of Q415 base-emitter signal current. Because of the feedback
configuration, the base of Q415 remains very close to the
0 V potential dictated by D416 and the base-emitter junc­
tion of Q415. The signal from the collector of Q427 drives
the left deflection plate of the cathode-ray tube and also
drives the Output Inverter amplifier.
R454, R457 and Q459 form an operational amplifier cir­
cuit with a gain of one, R457
(R
f
)
being equal to R454 (R;).
The inverted signal output from the Q459 collector provides
the right deflection plate with a signal which is equal and
opposite to that applied to the left deflection plate. C454
and C457 provide an adjustable high-frequency current path
to insure linear high frequency sweep operation.
The current flowing through the summing node at the base
of Q415 determines the circuit output voltages, and there­
fore the beam position. The POSITION control modifies
this summing node current by using a dual potentiometer
arrangement for coarse and fine positioning. The fine po­
tentiometer (R409B) has its pickoff voltage connected through
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