Tektronix 465B User Manual

Theory of
Operation—465B Service
Horizontal Display
Switching
Switching transistors
Q4482 and Q4481 are controlled
by
the Horizontal Display
Logic circuit. They are switched
off and on as
required to allow A sweep output
transistor
Q4475 and B sweep
output transistor Q4465 to pass
the A
or B
sawtooth
to
the Horizontal Amplifier.
When HORIZ DISPLAY is set to A, a
LO on the base of
Q4481 keeps the
transistor biased
off.
The A sawtooth is
allowed to pass to the
emitter
of
Q4475 to be amplified and
sent to the
Horizontal Amplifier. A
HI
on
the
base
of Q4482
turns it
on,
and
the
B
sawtooth
passes to
ground through
the
transistor, thereby preventing
the B sawtooth from
going
to
the
Horizontal Amplifier. The same conditions
exist when the HORIZ DISPLAY is set to
A INTEN. Setting
the
HORIZ DISPLAY to ALT will cause
the Horizontal
Display
Logic circuit to
alternately turn Q4481 and Q4482
off and on
to
first pass
the
A sawtooth
and then the B
sawtooth to
the Horizontal Amplifier.
When the HORIZ
DISPLAY is set to
B DLY'D, Q4482 will be biased off and
Q4481 will be on. The B sawtooth
will
go to
the Horizontal
Amplifier, and
the A sawtooth will be shunted to
ground.
HORIZONTAL DISPLAY LOGIC
Introduction
The
Horizontal Display
Logic
circuit produces the
signals that switch the A and B Sweep Generators and
the
A Sweep and B Sweep Z-Axis Gates. It also provides a
Vertical Alt Sync pulse
to the Vertical Switching circuit.
Switching transistor Q4398 enables the TRACE SEP
potentiometer (R14498) during ALT Horizontal Display.
Vert Alt Sync Pulse
A gating circuit is formed by U4391B and U4391D to
control the Vertical Alt Sync pulse.
The
pulse is used in
the
Vertical Switching circuit for clocking U1705 whenever
the ALT Vertical Mode
is
selected. In all Horizontal Display
modes except ALT, a HI at
pin
6 of U4391B
will
put a LO at
pin 3 of U4391 D. Pin 2 of U4391 D
has the positive-going
Horiz Alt Sync pulse
present. This pulse
is
inverted
through U4391 D and fed
tothe Vertical Switching circuit.
In ALT Horizontal Display mode, pin 6 of
U4391B will be
LO, and the signal at
pin
5 will control output pin
4. The
signal present at
pin 6 of U4491A, which changes state
with every
Horiz Alt
Sync pulse,
now controls U4391
D,
and
the Vert Alt Sync pulse becomes a
rectangular
pulse
having
a
period equal
to
twice the time between Horiz
Alt
Sync pulses.
Trace Separation
Transistor Q4398 acts as a switch to control the
enabling voltage to
TRACE SEP potentiometer R14498. In
the ALT
Horizontal Display mode the voltage is applied
to
the potentiometer during the
B Sweep time
to
supply
an
offset signal
to
Q2140 and
Q2130 in
the Vertical Output
Amplifier. This circuit allows control of the vertical
separation between the A Sweep
display
and
the B Sweep
display on the crt. During B Sweep, in ALT
Horizontal
Display
mode, a
HI will
be
present
on
pin4of U4391B. The
HI
will
raise
the
base voltage of Q4398 to turn it on and the
-8
volts on the emitter will be supplied to the TRACE SEP
potentiometer.
A
and B Sweep Switching
Flip-flop U4491 A controls Horizontal Display Switch-
ing transistors
Q4482 and
Q4481 in
the A
and
B Sweep
Generators.
The HORIZ DISPLAY switch
S6260 sets
the
flip-flop input
to
do one of the following:
1.
Turnoff
Q4481 and
turn on Q4482 to
allow the A
Sweep signal
to go to
the Horizontal Amplifier;
2.
Turn off Q4482 and turn on Q4481
to
allow the B
Sweep signal to go to the Horizontal Amplifier; or
3.
Alternately
turn
the two transistors off and on to
display both sweeps in ALT Horizontal Display mode.
U4491A
is
clocked
by
the Horiz Alt
Sync
when the
Horizontal Display
is
set
to
ALT. When the Horizontal
Display is set to A, A
INTEN, or
B
DLY’D, the state
of
the
outputs of U4491A is
determined
by
the logic levels
present at
pins 1
and 4. The HORIZ DISPLAY switches set
these logic levels.
Flip-flop U4491B controls
the
A and B Sweep
Z-Axis
Gate
switching transistors Q4492
and
Q4491. These
transistors
switch the biasonCR728l andCR738l
in
the A
and B Sweep Z-Axis Gates to
either
allow
the unblanking
gates to pass to
the Z-Axis Amplifier
or
block them.
U4491 B
is controlled by both the signal on pin 5 of U4491
A
and the A position of the
HORIZ
DISPLAY
switch.
HORIZONTAL
AMPLIFIER
Introduction
The Horizontal Amplifier circuit provides the output
signals to the crt horizontal deflection plates. The signal
applied
to
the
input of
the Horizontal Amplifier
is
deter-
mined by the TIME/DIV switch and the HORIZ DISPLAY
switch. This signal can come from either the sweep
generators within the instrument or some external signal
applied
to
the CH 1 OR X input connector (X-Y Horizontal
Display). Horizontal positioning, X10 magnifier circuitry,
and the horizontal portion of the beam finder
circuitry are
also contained in
the Horizontal
Amplifier. Figure
3-8
shows
a
detailed block diagram
of
the Horizontal Amplifier
circuit.

Tektronix 465B Specifications

General

Brand	Tektronix
Model	465B
Category	Test Equipment
Language	English