Horizontal Display Logic; Horizontal Amplifier - Tektronix 465B Instruction 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
U
4491
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
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.