the magnitude to be expected. A
near normal operations encoun-
listing of dc voltage is also included
tered, faully parts isolation pro-
to supplement the information pro-
cedure will be specified. The test
vided by the signal voltages. The
results, which are recorded i n
order of the dc voltage list follows
various test steps, are compared to
the dc distribution route in the
a normal indication. All of the con-
plug-in assembly circuit.
ditions included must be satisfied
(2) Except for inductor L7401 inplug-
before a normal indication has
in assembly A7400, all trans-
occurred. If a normal indication
former windings and coils used in
is obtained in the first test, the
the TS-1777/VRM-l have dc resis-
second test will be performed. This
tances of less than 1 ohm. Inductor
process continues, with successive
normal indications, until the final
L7401 has a dc resistance of 800
ohms .
test normal indication is obtained.
(3) Do not attempt very small angular
55. Isolating Troubles in Assembly A7400
a d j u s t m e n t s on variable trans-
formers or coils. The slug is se-
Refer to figure 39 for circuit details and
cured with a semirigid cement and
may spring back and thus nullify
a. Preparation.
(1) Connect the equipment as de-
the adjustment. Turn the adjust-
scribed in paragraph 32.
ment at least one-half-turn and
return to the initial setting and pro-
( 2 ) Set TS-1777/VRM-l selector
switch S7902 to position 10.
ceed from there as required. When
(3) Adjust the TS-382F/U for a fre-
the alignment is completed, use a
fine camel's-hair brush and brush
quency of 1,000 cps with an output
of O volt and connect it to the test
Minnesota Mining and Manu-
facturing type EC-800 cement or
probe.
(4) Connect the ME-30 B/U to con-
equivalent on the threads to secure
nector P7401-M.
the slug. Apply the cement verti-
cally across the threads and onto
(5) Connect the ME-26 B/U to con-
nector P7801-H and adjust it to
the case at three equally spaced
indicate + volts dc on the 30-volt
positions.
scale.
(4) After the maintenance has been
b. Gain Test.
completed, remove the plug-in as-
(1) Adjust the TS-382 F/U output for
sembly from the TS-1777/VRM-l
an ME-30 B/U indication of 50 mv.
and replace the original good plug-
(2) Adjust potentiometer R7406 for a
in assembly. Before attempting
maximum indication on the ME-
final testing of a repaired AN/
26B/U. A normal indication should
VRM-1, perform the adjustment
be +4.0 dc minimum.
procedures s p e c i f i e d in para-
(3) Increase the TS-382F/U output to
100 mv as indicated on the ME-
d. Isolation.
30B/U. A normal indication should
(1) Isolation is the process wherein
be +5.5 volts dc minimum.
faulty parts are located and sub-
(4) If the indications obtained in (2) or
sequently replaced. An externally
(3) above are low or absent, pro-
generated test signal is supplied to
ceed to d below.
the module, and signal voltage
m e a s u r e m e n t s are taken at se-
c. Bandwidth Test.
(1) Adjust the TS-382F/U for an ME-
lected circuit points. Typical sig-
30 B/U indication of 50 mv.
nal voltages are listed for those
( 2 ) Adjust potentiometer R7406 for an _
circuit locations to provide infor-
ME-26B/U indication of +3 volts
mation concerning the n o r m a 1
dc.
presence or absence of signal and
56
