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 TM 55-1905-220-14-11
5-155. LOUDHAILER - MAINTENANCE INSTRUCTIONS (Continued).
LOCATION
ITEM
ACTION
REMARKS
TESTS
4. Microphone.
The microphone unit can be given a preliminary check by removing the microphone cover (step 1), making the
insulated feed thru terminals accessible. Turn the volume control to high and check the resistance across these
terminals. A normal microphone unit will give a reading close to 30 ohms and in addition a click will be heard in the
microphone.
5. Loudspeaker
The loudspeaker driver unit can be given a preliminary test before tests are initiated on the amplifier module.
Remove the rear housing from the driver unit head as described in step 2. Setting the horn on its bell permits easy
access to the driver unit with the housing hanging alongside by the connecting wires, as shown. Remove the snap on
connectors from the amplifier output tabs marked "LINE" and "COM". Check the driver unit resistance across the "LINE"
and "COM" terminals for a normal reading close to 10 ohms. A click should be heard in the loudspeaker at the same
time. If no trouble has been found up to this point further tests must be made on the amplifier.
6. Amplifier
a. Refer to the electrical schematic of the Loudhailer.
b. Positive and negative buses are designated test points, as either one or the other are used in checking the normal
voltages or resistances of the circuit.
(1)
Preliminary. In order to troubleshoot the amplifier, the module must be removed from the rear housing. First
disconnect the six wires by removing the snap-on connectors from the tabs on the chassis. Remove the three amplifier
mounting screws (12). Slide out the amplifier module from the housing and place on a working surface, with the power
transistors down. Remove the two screws (43), and flatwashers (44) which secure the phenolic board to the assembly.
This board can now be hinged up and put on its cable and lid flat as shown in the illustration.
5-1601
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