Figure 16 - Negative Heat Sink Tests.

Figure 13 - Removing Drive End Housing From Rotor Shaft.

TM-5-3820-256-24-4 Drilling System Well Rotary Truck Mounted Air Transportable 600 Feet Capacity Model LP-12 NSN 3820-01-246-4276 Manual
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HEAVY DUTY ALTERNATORS Figure 16 - Negative Heat Sink Tests. 2. Reverse the test leads so that the positive test lead is connected to the negative heat sink. Touch the negative lead to each of the three diode terminals (Test 2, Figure 16). A low resistance reading should be obtained, and if a test light is being used, the lamp should light. If high resistance is indicated or the lamp does not light, the diode is open. See IMPORTANT. IMPORTANT - WHEN MAKING DIODE TESTS, SOME OHMMETERS MAY INDICATE RESULTS OPPOSITE OF THOSE SHOWN IN TEXT (I.E. A HIGH RESISTANCE WHEN TEXT CALLS FOR LOW RESISTANCE, ETC.). REGARDLESS OF THIS, EACH DIODE SHOULD GIVE ONE HIGH READING AND ONE LOW READING, IF BOTH READINGS ARE THE SAME, DIODE IS FAULTY. If a shorted or open diode is detected in the preceding tests, the entire heat sink assembly should be replaced. Heat sinks supplied as service replacements may differ slightly in thickness or general appearance from the original parts. This will in no way impair their interchangeability or reliability. To obtain the maximum serviceability, several different assemblies may be used as replacements. These will be listed in the appropriate parts list. CAPACITOR TEST The capacitor connected across the heat sinks may be tested on a capacitor tester if available. Its value is .5 MFD, and 200 working volts D.C. In the absence of a capacitor tester, the unit may be checked for shorts by means of an ohmmeter connected across the terminals. A low resistance reading indicates a shorted or leaking capacitor which should be replaced (See Figure 17). Figure 17 - Testing Capacitor. VOLTAGE REGULATOR TEST The regulators used in these alternators cannot be tested with ordinary test equipment. The easiest way to check a regulator is to install it in an alternator which is known to be in good working condition. Perform the voltage adjustment procedures shown in VOLTAGE REGULATOR ADJUSTMENT. If the alternator output cannot be modified or if the output voltage is unstable, the regulator must be replaced. ROTOR TEST The rotor should be checked for grounds and proper coil resistance with an ohmmeter. 1. With the ohmmeter connected between the rotor shaft and either slip ring, no reading (infinity) should be obtained. If an ohmmeter reading other than infinity is obtained, the rotor coil is grounded and the rotor must be replaced (See Figure 18). Figure 18 - Rotor Coil Ground Test. CTS-4043A - Chapter II - Page 8

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