C. Trouble shooting of circuits and components of the electrical generating and distribution systems is accomplished by utilizing the annunciator system, the warning and control systems and the electrical meters, battery and galley power module (P5-13) shown on diagram 24-28-11A as circuit analyzers. Switches on the forward overhead panel permit the use of airplane electrical meters and temperature indicators. The annunciator panel (module M238), located on the upper inner surface of the P6 panel, and shown on the diagrams 24-25-01, 24-27-21, and 24-35-01, contains lights which indicate when power is on the ac and dc busses and the cause of interruptions to the ac generators. A press-to-test button and an erase switch are provided for the ac generator annunciator lights. Connectors and checkout receptacles are located at various locations about the distribution system such as the power system test module M400 shown on wiring diagrams 24-28-21 and 24-28-31 and the P6-6 panel, on the load control center, where test apparatus and meters may be connected for circuit and component analysis.
D. Do not use meter probes in checking circuits from connectors, rather connect the meter, instrument or analyzer to a connector and make al1 connections by joining connectors, thereby avoiding joint or socket damage to connectors. The convenience afforded by the use of connectors may be offset by the trouble, which these connectors can cause if damaged by abuse or misuse. That is, extreme care must be exercised in opening and particularly closing electrical connectors or pin and wire damage will result. Connectors, which are suspected of mechanical damage or have collected moisture must be carefully cleaned and repaired. Succeeding cases of trouble may result from connector damage resulting from previous trouble shooting. That is, do not cause future troubles while trouble shooting.
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TROUBLE PROBABLE CAUSE ISOLATION PROCEDURE REMEDY
Transfer bus lights on generator annun-ciator panel go off and transfer bus off lights on pilots’ overhead panel come on Loss of power on transfer bus due to shorting of hydraulic B system pump transient suppression diodes Check transient suppression diode CR4 for No. 1 hydraulic pump and diode CR8 for No. 2 pump for shorting. Diodes are located in P5 hydraulic pumps module Replace faulty diode and reset 5-amp circuit breaker on generator control panel
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4. Inflight or Ground Checkout Analysis of Electrical Generation System Malfunctions
A. When a component in the electrical generation system fails to function properly during normal operation, evidence of this usually appears (1), as a signal on the annunciator panel (2), as an indication of circuit changes on the forward overhead panel (3), as a deactivation of a portion of the system due to failure of a piece of apparatus (4), as a trip action of a protective device following a sequence of events within the system (5), as an incorrect meter reading. Aside from a difference in general response of the entire airplane due to a major power failure, a malfunctioning unit or system will usually be made evident by one or more of these five categories.
B. The following listed failures are correlated with operating conditions as indicated by meters, switches and lights on the annunciator and pilots' center and forward overhead panel. To use the tabulated conditions, complete the analysis by locating the operating condition prevailing for the failure as listed in the tabulation Table I. The possible causes of the malfunction are given in the code to text references in the right-hand column of the tabulation.
C. AC Generator
(1)
Drive shaft or stub shaft has failed.
(a) Operate engine with generator control (field) relay open. Check for generator rotation by measuring generator residual voltage. If 12 to 19 volts ac are indicated at the voltage regulator terminals T1, T2 and T3 to ground, the generator is rotating.
(2)
Exciter field is open or shorted.
WARNING: AVOID CONTACT WITH METER TERMINALS AND EXPOSED WIRES WHEN MAKING TESTS WITH POWER ON THE AIRPLANE.
(a)
Trip GCR generator control (field) relay by placing GEN No. 1, No. 2 or APU GEN switch to OFF. This will open the main generator breakers.
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