TM 11-5895-846-14
Table 8-8. Alarm Monitor Power Supply, Troubleshooting Chart
Item of Check
Test Conditions
Normal Indications
Remarks
WARNING
DANGEROUS VOLTAGES EXIST IN THIS EQUIPMENT. Do not attempt any removal or replacement unless the equipment is in a non-operating
condition and all power circuit breakers on the power distribution panel are in the OFF position.
a. Perform the procedures of
1. Preliminary setup.
to the 110 volt position and the
power switch to OFF.
c. Connect the variable transformer
power line cord to a 115 volt, 50/
60 Hz power source.
a. Place the test fixture LOAD
2. Dc regulated
voltage adjust-
switches to the F.L, position and
ment, 115 Vac
the POWER LINE CIRCUIT BKR.
input, full load
to the ON (up) position.
output.
(DMM) to PWR. LINE T. P.
HIGH A (E) and NEUT C (D) test
points.
c. Turn on the variable transformer
and adjust the control for 115 t
0.5 volts on the DMM. Move the
DMM test leads to the E and D
test points and observe the same
voltage reading.
d. Measure each of the de outputs.
+ 24 t 0.24 V, 0.5 A
The + 24 Vdc regulator, U1,
Connect the second DMM in turn
+ 5 0.05 V, 0.75 A
is the voltage source for
(left-to-right) to each VOLTAGE
+ 15 0.15 V, 0.5 A
the + 15 Vdc regulator, U2.
T.P. and the clip-on millammeter
-15 t0.15 V, 0.5 A
The latter, in turn, is the
to the associated CURRENT T.P.
source for the - 15 Vdc
jumper (observe clip-on polarity).
regulator, Q12, Q13 (a
If necessary, adjust the appropri-
differential pair), and the
ate voltage control on the power
+ 5 Vdc regulator, U3.
supply to obtain the correct volt-
Therefore, if the + 24 Vdc
supply is faulty, the + 15
NOTE
Vdc supplies will be af-
The test fixture is a simulated,
fected. Also, if the + 15
not actual, load on the
Vdc supply is malfunc-
power supply. Therefore, cur-
tioning, the - 15 Vdc and
rent indications are nominal and
the + 5 Vdc supplies will
for referency only.
be affected.
If a supply voltage indica-
tion is abnormal and it
cannot be set to the normal
indication, check for
a fault in the regulator
stage of the associated
supply. See power sup-
ply schematic, figure
a. On the test fixture, place the LOAD
3. Line and load reg-
ulation, half-load
switches to the H. L. position.
b. Observe the DMM connected to the
output.
PWR. LINE test points and adjust
for 126.5 0.5 Vac on the DMM.
c. Measure each de output voltage
+ 24 t 0.24 V
If a supply voltage indica-
with the DMM at each VOLTAGE
+ 5 t 0.05 V
tion is abnormal, check
T.P.
+ 15 0.15 V
the associated circuits
-15 0.15 V
as follows: regulator IC
(U1, U2, Q12-Q13, or
U3), series regulator
transistor (Q1, Q8, Q1O,
8-18