Section VIII
Model 3455A
SERVICE GROUP G
8-61.
MISCELLANEOUS TROUBLESHOOTING.
8-G-2.
Powar Supplin ISchsmatic
It).
a. In many of the 345SA's power
supplies,
the voltage reference of
one
supply
is
the output
of
another. This arrangement ties the voltages of the two supplies together. A shift in one supply is
reflected in the other supply.
b. To isolate dependent supply circuits, the reference supplies should be separate from each other
and from the circuits they supply. The
following
steps may be used.
1
. Use
external supplies
to
provide
a
reference
to
dependent supplies.
2. Use external supplies to
drive
circuits in place of internal supplies.
c.
Following
are some
voltages of
the
inguard power supplies.
1. Main power
supply
voltages.
AlOTPll: +9 V to +11
V
A10TPI2: + 19.5
V
to +23.5
V
A10TP13: -19.5 V
to
-23.5 V
A10TP14: +38 V
to
+44 V
A10TP15:
-38
V
to
-44
V
AIOTP + 9: + 8.1 V to + 9.9 V (Inguard processor must be installed).
2. Ohms supply
voltages
AlOTl pins 1 and 3: 10 V rms (20 V peak to peak) square
wave.
AlOTl and AI2T1 connection: .2
V
rms (.25
V
open circuit) square
wave.
A12T1 pins
1
and 3:
40 V
rms (80
V
peak to peak) square
wave.
3.
Allowable
noise on the
ohms supply
as
measured with
a
true rms voltmeter.
+ 6.2 V
supply:
30
<iV noise
-6.2
V supply:
60
/iV
noise
d. If the fuse of the 3455A keeps
opening,
check the
AlO
board
power supply breakdown
diodes
(A10CR64,
66,
etc.).
Also,
make sure
the 3455A has been switched to the correct line voltage.
e.
Table 8-C-l lists the various components and assemblies
which
uses the
individual power
sup-
plies. This
table
may be useful
if
a power supply is loaded down by a
defective
component or
assembly.
Table B G-1. Power Supplies Locetions.
1 lu (
M nr
1
1
«
S »
T
1
9
M 11 1) 14 la la
If :a
86 n
21 II
M
hi » A D «e< AC 2
5 a t «a
•
iOi, X
X .
,
•
2R 3V
V
•
18
V
a
A
*
a
iv
*
x*A«#»*
1 a
“T
IS V 1 t X t
•
8 G-3.
Reference Assembly (Schematic
5).
a. The reference assembly of the 3455A is on the exchange program and should be returned to the
8-76
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