Specifications
near normal operations encoun-
tered, faully parts isolation pro-
cedure will be specified. The test
results,
which are recorded i n
various test steps, are compared to
a normal indication. All of the con-
ditions included must be satisfied
before a normal indication has
occurred. If a normal indication
is obtained in the first test, the
second test will be performed. This
process continues, with successive
normal indications, until the final
test normal indication is obtained.
(3) Do not attempt very small angular
adjustments on variable trans-
formers or coils. The slug is se-
cured with a semirigid cement and
may spring back and thus nullify
the adjustment. Turn the adjust-
ment at least one-half-turn and
return to the initial setting and pro-
ceed from there as required. When
the alignment is completed, use a
fine camel’s-hair brush and brush
Minnesota Mining and Manu-
facturing type EC-800 cement or
equivalent on the threads to secure
the slug. Apply the cement verti-
cally across the threads and onto
the case at three equally spaced
positions.
(4) After the maintenance has been
completed, remove the plug-in as-
sembly from the TS-1777/VRM-l
and replace the original good plug-
in assembly.
Before attempting
final testing of a repaired AN/
VRM-1, perform the adjustment
procedures s p e c i f i e d in para-
graphs 41 through 43.
d. Isolation.
(1) Isolation is the process wherein
faulty parts are located and sub-
sequently replaced. An externally
generated test signal is supplied to
the module, and signal voltage
measurements are taken at se-
lected circuit points. Typical sig-
nal voltages are listed for those
circuit locations to provide infor-
mation concerning the n o r m a 1
presence or absence of signal and
the magnitude to be expected. A
listing of dc voltage is also included
to supplement the information pro-
vided by the signal voltages. The
order of the dc voltage list follows
the dc distribution route in the
plug-in assembly circuit.
(2) Except for inductor L7401 inplug-
in assembly A7400, all trans-
former windings and coils used in
the TS-1777/VRM-l have dc resis-
tances of less than 1 ohm. Inductor
L7401 has a dc resistance of 800
ohms .
55. Isolating Troubles in Assembly A7400
Refer to figure 39 for circuit details and
figure 29 for aid in locating the parts.
a. Preparation.
(1) Connect the equipment as de-
scribed in paragraph 32.
(2) Set TS-1777/VRM-l selector
switch S7902 to position 10.
(3) Adjust the TS-382F/U for a fre-
quency of 1,000 cps with an output
of O volt and connect it to the test
probe.
(4) Connect the ME-30 B/U to con-
nector P7401-M.
(5) Connect the ME-26 B/U to con-
nector P7801-H and adjust it to
indicate + volts dc on the 30-volt
scale.
b. Gain Test.
(1) Adjust the TS-382 F/U output for
an ME-30 B/U indication of 50 mv.
(2) Adjust potentiometer R7406 for a
maximum indication on the ME-
26B/U. A normal indication should
be +4.0 dc minimum.
(3) Increase the TS-382F/U output to
100 mv as indicated on the ME-
30B/U. A normal indication should
be +5.5 volts dc minimum.
(4) If the indications obtained in (2) or
(3) above are low or absent, pro-
ceed to d below.
c. Bandwidth Test.
(1) Adjust the TS-382F/U for an ME-
30 B/U indication of 50 mv.
(2) Adjust potentiometer R7406 for an _
ME-26B/U indication of +3 volts
dc.
56