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HP 435B Service Manual

HP 435B
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S
ERV
IC
ES
HEET
4
(Cont'd)
R
egulating
action of
t
he
24V
s
upply
is
started
by
C
R9,
R
58
and
R60
.
When
t
he
LINE
s
witch
is
set
to
ON,
c
urrent
b
egins
to
flow
t
hrough
R60
and
VR4
.
A
s
the
voltage
increases across
VR4,
current begins
to
flow
t
hrough
Q11
which
biases
Q13
and
Q16
on
.
The
r
egulator
output
b
egins
to
increase
in
α
n
egative
direction
.
The
output
voltagebiases
CR9
which,
in
t
urn,
causes
the
v
oltage
across
VR4
to
increase
.
The
r
esulting
r
apid
increasein
voltage
on
the
b
ase
of
Q
11
k
eeps
i
t
ahead
of
t
hat
on
theb
ase
of
Q10
.
When
t
he
Q11
b
ase
voltage
stabilizes
at
-12
Vdc,
the
l
ower
voltage
on
Q10
k
eeps
the
output
l
evel
increasing
until
it
approaches
-24
Vdc
.
A
t
this
p
oint
the
base
v
oltages
of
Q10
andQ11
b
ecome
equal,
the
differential
a
mplifier's
error
o
utput
goes
to
z
ero,
and
t
he
output
i
s
stabilized
at
-24V
.
C25andR61
f
orm
α
l
ow
pass
filter
which
reduces
the
high
gain
of
t
he
circuit
at
high
frequencies
thus
preventing
unwanted
oscilla-
tions
.
R
59
andC24
f
orm
α
n
oise
filter
for
t
he
z
ener diode
.
The
input
voltageto
the
24V
regulator
may
be
as
high
as
70
Vdc
from
t
he
line
voltage
or
as
l
ow
as
26
Vdc
f
orm
t
he
b
attery
.
12
V
S
h
unt
R
egulator
U
7
i
s
connected
as α voltage
f
ollower
c
ircuit
.
Chassis
ground
is
coupled
to
theinverting
input
of
U7
and
t
he
non-inverting
input
i
s
coupled
across
h
alf
t
he
24V
series
regulator o
utput
byα
voltage
divider
R63andR64
.
If
t
he
v
oltage
input
to
pin
3
tries
to
shift
toward+12
or
-12
Vdc,
theoutput
from
U7
w
ould
bring
the
vol-
tage
at
U
7
pin
3
b
ack
to
ground
potential
.
B
attery
Test
NOTE
Th
e
batte
ry
test c
ir
c
ui
t
i
s
in
ope
r
at
i
o
n
a
ny
t
im
e
t
he
LINE
sw
i
tc
h
i
s
set
to
ON
;
h
owe
v
e
r
,
t
h
e only
t
im
e
t
h
e
m
ete
r
indi
cat
i
o
n
i
s
m
ea
nin
gf
ul
i
s
w
h
e
n
t
h
e
batte
ry
i
s s
up
p
lyin
g
powe
r
.
W
hen
t
he
battery
is
supplying
p
ower
for
t
he
P
ower
Meter
c
ircuits,
and
t
he
b
attery
is
d
efective
or
discharged,
the b
attery
test
circuit
r
emoves
the p
ositive
(+12
Vdc)
supply
voltage
from
t
he
D
C
Amplifier
(A4U5)
.
This
causes
α
full
downscale
m
eter
indication
.
The
test
circuit
m
easures
αp
ercentage
of
t
he
voltage
difference
b
etween
t
he
-12V
o
utput
and
t
he
n
egative b
attery
terminal
.
As
this
v
oltage
difference
d
ecreases
to
approximately
3
Vdc,
Q14
Switc
h
Assembly
and
DC
Ampl/Auto
Zero
Ρ
/
ΟΑ
1
and
Ρ
/
Ο
Α
4
S
ERV
IC
ES
HEE
T

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HP 435B Specifications

General IconGeneral
BrandHP
Model435B
CategoryMeasuring Instruments
LanguageEnglish

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