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 TM 55-1905-220-14-11
5-117. SHIP'S COURSE INDICATOR - MAINTENANCE INSTRUCTIONS (Continued).
LOCATION
ITEM
ACTION
REMARKS
OVERHAUL-TEST
5. Electrical Test
CAUTION
Do not measure resistances between circuit points.
Ohmmeter test voltages can damage semiconductor
devices such as the diodes and transistors used in
ship's course indicators.
a. Remove all power and synchro signals at a point external to the indicator.
b. All circuits are isolated from the metal frame of the indicator. Ohmmeter tests, made with
a multimeter-type ohmmeter, between all terminals, and the metal amplifier chassis and between any
circuit point including lamp circuit and metal chassis should show resistance in excess of 10 megohms.
(Similarly, all terminals on the terminal block at the base of the indicator housing are insulated from the
case and should test at least 10 megohms from terminal to case.) If less than 10 megohms is measured,
check for frayed insulation or evidence of a shorted lead at the terminal board or in the cable external to
the indicator.
c. Troubleshooting the amplifier.
(1) If, with the ship's course indicator deenergized, the rotating components turn freely
through a complete rotation of the dial, and if the rotating components check for continuity, the next step
is to check the amplifier.
CAUTION
Apply power only at the rated frequency for the indicator under test.
(2) First examine the amplifier for outward signs of failure: loose connections, broken leads, overheated
components. If the amplifier appears satisfactory, apply 115-volts at the specified frequency (Table 1-1) to the ship's
course indicator and, with an AC voltmeter with a sensitivity of at least 1000 ohms per volt, check measured voltages
against normal voltages (see table). A difference
5-1335
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