Tektronix 465B User Manual

Theory of
Operation—465B Service
supply level through R7184. Diodes CR7084, CR7085,
CR7097, and CR7098
provide protection
against acciden-
tal
application
of
damaging voltage levels
to
the
A -1-Gate
and
B -1-Gate output connectors.
Horiz
Alt Sync Pulse Amplifier
The pickoff amplifer for the Horiz Alt Sync pulse
is
Q7174. It
is
biased into saturation, so its quiescent output
voltage
is
approximately zero.
A
sample of the
A
-1-Gate
is
coupled to
the base
of
Q71
74
by C71
74 where the positive-
going gate is integrated by the action of C7I74 and R717I.
The positive-going
portion of the integrated signal cannot
increase
the collector current of
Q7174 beyond
its satura-
tion level, so no signal output is obtained.
When the
A
-1-Gate negative-going edge occurs.
C7174
cannot change
its charge
instantaneously
so
the entire negativetransition
is
felt
on
the
base
of Q7174 across R7171. The negative
peak of the signal is enough to cutoff Q7174, and
the
collector voltage rises
in
response to the base voltage
decrease. The base voltage rapidly returns to a positive
level,
and
the transistor
again
saturates,
ending
the Horiz
Alt
Sync
pulse.
A
AND B SWEEP GENERATORS
Introduction
The
A
and B Sweep Generators produce
sawtooth
voltages which are amplified
by
the Horizontal
Amplifier
circuit to provide horizontal deflection on the
crt.
These
sawtooth voltages are produced
on
command (Sweep
start gate)
from the
Sweep Logic circuits. The Sweep
Generator
circuits also
produce
gate waveforms that are
used by
the 2-Axis Logic
circuit to unblank the crt during
sweep time
and by
the Sweep
Logic circuit to terminate
sweep generation. Figure 3-7 shows
a
detailed
block
diagram of the A Sweep Generator circuit that will
be
described in the following discussion. Since the B Sweep
Generator circuit is very similartothe
A
Sweep Generator,
the only
discussion of
the B
Sweep
Generator will be on
the differences in operation between the two.
Disconnect Amplifier
After
holdoff,
but
before
the next sweep, Disconnect
Amplifier Q4497 is biased on and conductsthrough R4587
and Ri
back
to +V
t
.
This
sets
the
charge on
C,
in
preparation for the beginning of the next
A
Sweep
and
prevents current from the Miller Integrator circuit from
SAWTOOTH
OUTPUT
TO HORIZONTAL
AMPLIFIER
Q4498
Q4598
3-16
REV A
JUN 1979

Tektronix 465B Specifications

General

Brand	Tektronix
Model	465B
Category	Test Equipment
Language	English