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S
ERVIC E
S
HEET 4 (Cont'd)
R
egulating action of
t
he 24V supply is started by C R9,
R
58 and
R60. When
t
he LINE switch is set to ON, c urrent b egins to flow
t
hrough R60 and VR4.
A
s the
v
oltage 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 negative direction .
The output
v
oltage biases CR9 which, in
t
urn, causes the
v
oltage
across VR4 to increase . The
r
esulting rapid increase in voltage on
the base of Q11
k
eeps
i
t ahead of
t
hat on the base ofQ10. When
t
he
Q11 base
v
oltage 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 point the base
v
oltages of Q10 and Q11 b ecome equal, the
differential a mplifier's error o utput goes to zero, and
t
he output
i
s
stabilized at -24V.
C25 and R61
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 and C24
f
orm α noise filter for
t
he zener diode.
The input
v
oltage to the 24V regulator may be as high as 70 Vdc
from
t
he line
v
oltage or as
l
ow as 26 Vdc
f
orm
t
he b attery .
12 V
S
h unt Regulator
U
7
i
s connected as α
v
oltage
f
ollower circuit. Chassis ground is
coupled to the inverting input ofU7 and
t
he non-inverting input
i
s
coupled across half
t
he 24V series
r
egulator
o
utput by α
v
oltage
divider R63 and R64. If
t
he
v
oltage input to pin 3 tries to shift
toward +12 or -12 Vdc, the output from U7 would bring the vol-
tage at
U
7 pin 3 back to ground potential .
B attery Test
NOTE
The batte ry test cir cuit
i
s in oper ation any
t
ime th e
LINE switch i s set to ON;
h
owe ve r, t he only
t
im e
the mete r indication is meaningful i s when
t
h e
batte ry is supplying powe r.
W hen
t
he battery is supplying power for
t
he
P
ower Meter circuits,
and
t
he battery is defective or discharged, the
b
attery test circuit
r emoves the positive (+12 Vdc) supply voltage from
t
he
D
C
Amplifier (A4U5) . This causes α full downscale meter indication .
The test circuit m easures α percentage of
t
he
v
oltage difference
b etween
t
he -12V
o
utput and
t
he negative battery terminal. As
this
v
oltage difference decreases to approximately 3 Vdc, Q14
Switch Assembly and DC Ampl/Auto Zero
Ρ/Ο Α 1 and Ρ /Ο Α4
S
ERV ICE
S
HEET
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