TM 5-6665-202-13
d. Testing and Repair. Test headset by re-
threads in setscrew hole, or other defects. In-
moving lead from terminal no. 4 on A5 Board
spect variable resistors and control switch for
proper operation when shaft is turned.
(Receiver transmitter assy). Connect ohmmeter
to removed lead and ground. An approximate
(3) Replace all damaged or defective com-
resistance reading of 150 to 300 ohms should be
ponents.
c. Reassembly. Reassemble the control box in
obtained. Place headset to ear and touch multim-
eter lead to disconnected headset lead. A distinct
the reverse order of numerical sequence as illus-
click should be heard in each ear phone if head-
trated in figure 6-5.
d. Testing.
set is functioning properly. If there is no indica-
(1) Fixed resistors. Test the fixed resistors
tion in the headset, or 150 to 300 ohms is not
indicated on the multimeter, the headset is defec-
(1, fig. 6-5). The resistance reading should be
tive and must be replaced.
between 1,995 and 2,005 ohms. If resistance
reading is other than specified above, the resis-
NOTE
tor is defective and must be replaced.
Audio Sears model headset is 160 ohms and
Roanwell model headset is 300 ohms.
(2) Test fixed resistor (3, fig. 6-5). The
NOTE
resistance reading should be between 78 and 86
Perform the above test in the same manner on
ohms. If the resistance reading is other than
both ear pieces. If one earpiece is operative and
specified above, the resistor is defective and must
the other one is defective, the complete earphone
be replaced.
assembly must still be replaced.
(3) Test fixed resistor (7, fig. 6-5). The
e. Installation. Refer to figure 5-1 and install
resistance reading should be between 4,257 to
the headset assembly.
4,343 ohms. If the resistance reading is other
6-4. Control Box
than specified above, the resistor is defective and
must be replaced.
a. Disassembly. Disassemble the control box
(4) Test fixed resistor (9, fig. 6-5). The
in the order of numerical sequence as illustrated
resistance reading should be between 2,980 and
by figure 6-5.
3,040 ohms, if the resistance reading is other
b. Cleaning, Inspection and Repair.
than specified above, the resistor is defective and
(1) Clean all metal parts with an approved
must be replaced.
cleaning solvent and dry thoroughly, Clean ter-
(5) To test the variable resistor (8, fig. 6-
minals and contacts with a clean dry cloth. Clean
5), rotate the screw (located in the end of the
variable resistors with electrical control cleaner
resistor) clockwise for maximum resistance and
(FSN 6850-664-5641). Wipe all plastic and
counterclockwise for minimum resistance. Values
fiber components with a clean, dry cloth.
of resistance should vary from 0 to 2,000 ohms.
CAUTION
If no reading is obtained or the value indicated
When cleaning components with clean-
on the meter is above 2,000 ohms, the resistor
ing solvents, do not allow the solvents
is defective and must be replaced. Test total re-
to come in contact with the plastic com-
sistance with a Wheatstone Bridge. Disconnect
ponents of the control, as most cleaning
yellow lead of resistor on TB1-1 and connect
fluids are harmful to plastics.
multimeter to TB1-6 and the disconnected yel-
low lead in order to make this test.
(6) Test variable resistor (16, fig. 6-5).
Resistance should read from 0 to 1100 ohms. If
Avoid prolonged breathing of cleaning
resistance reads above 1,100 ohms or no reading
solvents. If it becomes necessary to
is obtained as the resistor shaft is rotated in
breath any amount of solvents venti-
either direction, the resistor is defective and
late the area as much as possible. Pro-
must be replaced. Test total resistance with a
longed breathing of solvents may be
Weatstone Bridge. In order to test resistor, dis-
harmful and injurious to health.
connect yellow and white lead from terminal
(2) Inspect resistors and terminal connec-
board A5 terminal no. 7. Connect multimeter to
tions for breaks, corrosion, or other defects. In-
ground and disconnect lead.
spect control chassis for breaks, cracks, damaged
(7) Test variable resistor (19, fig. 6-5).
threaded areas, or other defects. Inspect knob
Resistance should read from 0 to 525 ohms as
covers for breaks, cracks, or other defects. In-
resistor shaft is rotated. If resistance reads above
spect knobs for chips, nicks, scratches, damaged
525 ohms or no reading is obtained as shaft is
6-6