Testing Rectifier - TM-5-4240-501-14P

Testing for Short in Stator or in Rectifier

Condition Found (Fuse Blown)

TM-5-4240-501-14P Special Diver Air Support System (SDASS) NSN 4220-01-292-3708 Manual
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ALTERNATOR Dual Circuit- Fuse Type Fig. 182 - Checking for Grounded Charging Coils Testing Rectifier Attached to the blower housing baffle is a small black rectifier assembly. The rectifier is tested with a multimeter as follows: Three leads from the rectifier connect to pins in the detachable plug. See Figure 183. Leave rectifier installed on blower housing. Test rectifier with multimeter (using resistance scale) to check resistance from the red lead pin to blower housing (in an unpainted clean area). See Figure 183. After checking pin, reverse meter leads and recheck. The meter should show a reading in one direction only. If the rectifier pin shows a meter reading both ways, the rectifier is defective. If the pin shows no reading either way, the rectifier is again defective. Leaving one probe on blower housing, repeat with each black lead pin. Again meter should show continuity in one direction only, otherwise rectifier is defective. Now try between red lead pin and each black lead pin. Again, when probes are interchanged, meter should show continuity in one direction only. Fig. 183 - Testing Rectifier Testing Alternator AC Circuit (Lighting) Connect load lamp to AC output plug and ground as shown in Figure 184. Load lamp should light to full brilliance at medium engine speed. If lamp does not light, or is very dim at medium speeds, remove blower housing and flywheel. Disconnect ground end of AC coil, which is attached to the retaining clamp screw as shown in Figure 185. Fig. 184 - Testing AC Light Circuit Output With multimeter, check continuity between ground lead of AC coil and AC output terminal as shown in Figure 185. Meter should show continuity. Fig. 185 - Testing AC Circuit for Continuity Next, be sure ground lead terminal is not touching a grounded surface, and check continuity from terminal to ground. Meter should not show continuity. If meter indicates continuity, coils are grounded and defective. Examine both (white) leads to be sure the insulation is not worn or cut. Repair with tape and shellac if a bad spot is found. If ground still exists, or if AC coils do not show continuity, stator must be replaced. 57

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