Theory
of
Operation—2465B/2467B Service
_n
Z-AXIS
OUTPUT
(VZ
OUT)
\
+8V
TO
+73V
+8V
R4413
AA/V
13
AC DRIVE
FROM
PIN
OF T4340
+ 150V
OV
-150V
%
+ 10SV
+78V
+8V
n
R4412
CR4422
C4343 R4343
—1( VW-*-AAAA-
R4341
CR4342.
<sn
R4421
-AATv
15
PARTIAL U4310
D
C
He
B
A
E
-IX-AAA-^
n
/
-1900V
-1920V
-1985V
CONTROL GRID
CATHOOE
[
•
) DS4410
+42V
+42V
9-
GRID BIAS
R4354-
R4364
f
VW
U4366B
+~
S
\ R4333
t-AW—f-
R4372•
1
—wv
R4373
C4430,
CR4331
U4332A
+"\ R4332
t-AAAr-
i
^ CR4423
C4422
C4332
ne-
R4336
*
VW
/T7
^
Q4331
+42V
FROM ANODE
CURRENT
LIMITER
-15V
6019-06
Figure 3-10.
Dc
restorer circuit (2467B only).
During
the
time diode CR4423
is
reverse biased
(not
clamping
the
positive peaks), transistor Q4331
is
kept
biased
in the
active region
by the
charge retained
on
C4422 from
the
previous positive clamping cycle.
As the
positive amplitude
of the ac
waveform
at
Test Point
72
exceeds
the
voltage
at the
collector
of
Q4331,
diode
CR4423 becomes forward biased,
and the ac
waveform
is
clamped
at
that level.
Any
current greater than that
required
to
maintain
the
clamp voltage will
be
shunted
to
the
+
42-V supply
by
transistor
Q4331.
Operational amplifier U4332A sinks
a
time-dependent
variable current away from
the
base
of
Q4331 that
modifies
the crt
grid bias during
the
first
few
minutes
of
instrument operation.
The
circuit compensates
for the
changing grid drive characteristics
of the crt as it
warms
up.
At power-up, capacitor C4430 begins charging through
R4333 toward
the
Positive voltage
on pin 7 of
U4366B.
The voltage
is
relative
to the
setting
of
grid bias poten-
tiometer R4354.
The
output
of
U4332A follows
the
rising
voltage
on pin 3 and
after about
ten
minutes
(for all
practi-
cal purposes) reaches
the
voltage
on pin 7 of
U4366B.
As
the output voltage slowly increases,
the
charging current
through R4332 causes
the
Grid Bias voltage
to
gradually
decrease from
its
power-on level.
If
instrument power
is
momentarily turned
off and
then back
on, the crt
cathode
3-43
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