TM 11-6625-1683-15
Symptom
Probable tremble
Correction
f. RCVR-XMTR circuit breaker
f. With INPUT POWER switch S1
CB4 defective.
at OFF and circuit breaker CB4
at (ON, check continuity across
contacts 1 to 2 and 3 to 4.
Closed circuit should be indi-
cated; otherwise, replace circuit
breaker CB4.
g. Defective power converter block
g. Check for +300-volt output at
700.
TP62. If not indicated, replace
converter unit 700.
s o u r c e and INPUT POWER switch S1 is at
6-5. Checking Circuit Breakers
AC ON. The primary evidence of possible
Circuit breaker defects fall into two cate-
failure in this circuit is an absence of operat-
gories: mechanical failure and electrical fail-
ing voltages.
ure.
b. To localize this condition to the conver-
a. Mechanical Failure, This is evidenced by
t e r , with INPUT POWER switch S1 at ON,
a failure to maintain latching, when the cir-
check for the presence of 115 volts ac at the
cuit breaker is set to ON with no power in
input terminals of filters FL1 and FL2 (fig.
the circuit. Replace if necessary.
b. Electrical Failure. This is observed as an
ing taken by the multimeter at the terminal
open circuit condition with the circuit breaker
of filter FL3 referenced to ground should show
s e t to ON. A continuity test, with a multi-
approximately 6 volts.
meter in low ohms setting, taken across the
c. If this voltage is not available, failure
terminals of the circuit breaker will indicate
o f the converter is indicated and a detailed
i f closure is being effected. An open circuit
analysis is required. To do this, remove the
requires replacement of the component.
c o v e r of the shield. This provides access to
the interior.
6-6. Checking internal Power Converter
a. T h e i n t e r n a l c o n v e r t e r f u n c t i o n s o n l y
d. A listing of possible faults and corrective
w h e n p o w e r i s d e r i v e d f r o m a 115-volt ac
measures follows:
Symptom
Probable trouble
Correction
1. With 115 volts ac at input terminals
a. Replace rectifiers.
of filters FL1 and FL2, the multi-
rectifier CR1, CR2, CR3, and
meter set to provide a reading of
CR4 are defective.
100 volts dc connected across
b. One or more of bank of filter
b. Disconnect individual capacitors
capacitor C6, either no voltage is
capacitors C1, C2, C3, C4,
from terminal studs and, with
indicated or it is less than approxi-
C5, and C6 are shorted or
multimeter, check across each
mately 100 volts.
have electrical leakage.
for leakage resistance or shorts.
Observe correct polarity. Re-
versal will give erroneous read-
ing. Replace defective capaci-
tors.
2. With 115 volts oc at input terminals
a. Transistor Q1 or Q2 is defec-
of filters FL1 and FL2, connect
tive.
7-6) .
cathode-ray oscilloscope across ter-
b. Short or leakage condition in
b. Isolate and test each capacitor
minals 8 and 104 toroidal power
capacitor C10, C11, or C12.
6-4
AGO 7918A
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