Tektronix 422, Инструкция по эксплуатации

Страница: 55 / 213

Circuit Description—Type 422 AC-DC
( X I 0 MAG switch pulled out). Variable capacitor C537
provides high-frequency compensation fo r a linear display
(X I operation) at fast sweep rates. When the X I 0 MAG
switch is pulled out, resistive feedback is provided only
through R527 and capacitive feedback through C527-C528.
The feedback fo r X I 0 operation is about 1/1 Oth that fo r
X I operation so the circuit gain is increased 10 times. Vari­
able capacitor C527 provides high-frequency compensation
fo r a linear X I 0 magnified display at fast sweep rates.
Paraphase Output Amplifier
The output signal from the Feedback A m plifier is con­
nected to the base of Q544. Transistors Q544 and Q554 are
connected as a paraphase amplifier to convert the single-
ended input to a push-pull output signal which is necessary
to drive the horizontal deflection plates of the CRT. Circuit
operation is as follows: The positive-going sawtooth from
the Sweep Generator (or positive-going external horizontal
signal) is amplified and inverted through the Feedback
A m plifier stage to provide a negative-going signal at the
base o f Q544. This negative-going signal at the base o f
Q544 reduces its conduction and its collector goes positive.
This produces a positive-going sawtooth output signal at the
collector o f Q544 which is connected to the right deflec­
tion plate o f the CRT.
Transistor Q560 is connected as a constant current
source fo r Q544-Q554 with its output current determined
by divider R564-R565 and emitter resistor R562. When the
current through Q544 is reduced, more current is available
to Q554 through C556-R556. This increase in current fo r­
ward biases Q554, which is connected as a common-base
stage. The increase in current through Q554 produces a
negative-going sawtooth at its collector which is connected
to the left deflection plate o f the CRT. Thus the single
ended input signal has been amplified and is available as a
push-pull output signal.
C A L IB R A T O R A N D R EG U LATO R S
General
The Calibrator and Regulators circuit provides a square-
wave output w ith accurate amplitude. This output is avail­
able at the CALIBRATOR jack on the fro n t panel or it is
internally connected to the vertical deflection system in the
CALIBRATE 4 DIVISIONS positions o f both V O LTS/D IV
switches. This circuit also contains tw o regulator circuits to
provide regulated outputs o f +10.5 and —81 volts. In addi­
tion, this circuit provides the interconnections between the
power supply unit and the indicator and includes the v o lt­
age sources fo r the V A R IA B LE control UNCAL lights. Fig.
3-10 shows a detailed block diagram o f the Calibrator and
Regulators circuit. A schematic of this circuit is shown on
diagram 10 at the back o f this manual.
Calibrator
Transistors Q765 and Q775 are connected as an astable
m ultivibrator. Frequency o f operation is about one kilo-
hertz. Circuit operation is as follows: Assume that Q765
has just turned o ff and Q775 turned on. While Q765 was
on, C760 charged negatively on the Q765 side to a level
which is about 0.6 volt more positive than the em itter level
o f Q765. Now w ith Q765 o ff, C760 discharges 12
volts through R760. As C760 discharges, the anode o f
D760 follows and when it reaches a level about 1.2 volts
more positive than the base level o f Q765 (as established by
divider R765-R773), Q765 is forward biased. As Q765
turns on, its collector rises positive and pulls the base o f
Q775 positive through R763. Q775 turns o ff and its col­
lector drops negative to about —6.5 volts to reverse bias
D780. With D780 reverse biased, the voltage across o utput
divider R786-R787 is determined by the voltage applied to
it through D782 from R780-R781 and the - 8 1 -volt supply.
Calibrator Am plitude adjustment R780 is adjusted to pro­
vide an accurate tw o-volt peak-to-peak square-wave signal at
the CALIBRATOR jack on the fro n t panel. This also pro-
+ 55 V
+ 10.5 Volt
Regulator
Q 7 1 4 Q 7 1 7
D714
+ 10.5 V
-no v
— 81-Volt
Regulator
Q 73 4 Q 7 3 7
D739 V 739
------
— 81 V
Calibrator
Multivibrator
Q 765 Q 775
<
2 VOLT PROBE
CALIBRATOR
R786
1
R787
Calibrator signal
* to Channel 1 and
Channel 2 Input
Amplifiers
m
3-17
Fig. 3-10. Calibrator and Regulators detailed block diagram.