Tektronix 7623, Инструкция по эксплуатации

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Circuit Description— 7623/R7623 Service
Fig. 3-18. Vertical Amplifier detailed block diagram.
Input Balance
0407-0415 comprise a paraphase amplifier to provide
input balance for the Vertical Amplifier by changing the
DC levels at pins 2 and 4 of U450. Vertical Centering
adjustment R403 determines the bias at the base of 0407.
As this bias is changed, the levels at the collectors of Q407
and Q415 change due to paraphase action. This DC level is
connected to pin 2 of U450 through R408-R423 and to pin
4 through R414 R424. R403 is adjusted so the trace is
displayed at the center of the CRT when the inputs to this
circuit are at the same potential.
The input to the base of Q407 through J409 is used for
Vertical readout signal.
Output Amplifier
Amplification of the vertical signal is accomplished by
integrated circuit U450. The circuit shown within the
shaded area is a representation of the circuit contained
within U450. Notice that the circuit is made up of three
similar push-pull stages. Each stage has a pair of common
emitter transistors driving a pair of low input impedance
common base transistors. Frequency compensation is pro­
vided by the networks connected between pins 2 and 4 in
the first amplifier stage and pins 7 and 8, 13 and 14 in the
third amplifier stage. The resistive network connected to
pins 3, 6, and 16 determines the gain of the Vertical
Amplifier. Vertical Gain adjustment R447 sets the gain of
the second amplifier stage to determine the overall gain of
the vertical deflection system and thereby provide a
calibrated deflection factor. Bias adjustment R486 sets the
voltage level at pin 10 of U450 (nominally 4.3 volts) to
balance the third amplifier stage for maximum gain­
bandwidth operation.
Beam Finder Network
The Beam Finder Network, consisting of transistor Q496
and associated components, provides a means of locating a
display which overscans the graticule area. Under normal
operation, —15 volts is connected to the base of Q496 from
the BEAM FINDER switch (see diagram 4 and 9) to reverse
bias it. Therefore, the normal operating levels for U450 are
determined by the resistive network connected to pins 3, 6,
and 16. When the BEAM FINDER switch is pressed, the
— 15 volts is interrupted and the base of Q496 rises positive
to turn it on. The resulting change in current of U450
unbalances the second amplifier stage so as to limit its gain.
This action compresses the display vertically within the
display area.
HORIZONTAL AMPLIFIER
The Horizontal Amplifier circuit amplifies the push-pull
horizontal deflection signals from the plug in unit in the
horizontal compartment and connects it to the horizontal
deflection plates of the CRT. Fig. 3-19 shows a detailed
block diagram of the Horizontal Amplifier circuit. A
schematic of this circuit is shown on diagram 5 at the rear
of this manual.
Horizontal Channel Switch
The horizontal signals from the plug-in unit in the
horizontal compartment are connected to pin 2 and pin 15
of U510. The Readout signal is connected to pin 7 of
U510. Integrated circuit U510 determines which input
signal will provide the signal for the Horizontal amplifier
circuit as controlled by the X/Y Shutdown signal from the
Readout system. When the X/Y Shutdown is LO, the signal
from horizontal compartment is passed to the output of
U510. When the X/Y Shutdown is high, the Readout signal
is passed to the output of U510. Resistors R514, R515,
R521, and R522 establish the operating levels for this
circuit. R512 adjusts the circuit gain. R511 and R513
establish the range for the gain adjustment (see Trigger
Channel Switch under TRIGGER SELECTOR in this
section).
For normal operation, the gain and current level resistors
are connected to the Display Limit Command line. The
Display Limit Command is connected to the —15 supply
through the BEAM FINDER switch. When the BEAM
FINDER switch is actuated, the —15 volt is interrupted to
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