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1. General
A.  In an electro-hydromechanical and electronic system such as that used for AC generation, the location of trouble is not simple. Due to this fact a complete understanding of the system is quite essential. Symptoms of trouble may be difficult to interpret because protective devices function quickly, and in many instances the sequence of operation of protective devices is not noticed at the time of the original failure. For example if only a low voltage condition exists, as indicated on the annunciator panel, it will be noticed in the Annunciator Signaled Trouble Shooting Chart that several probable causes are given for the signal; "Low voltage light comes on, on the annunciator panel." Other observed symptoms may often be considered before the choice of one of the five causes is made to begin the isolation procedure. The annunciator signaled trouble shooting charts, prepared as a guide as well as a procedure, are used in the following manner:
(1)  
Notice the signals on the annunciator panel.

(2)  
Consider the probable cause.

(3)  
Eliminate probable causes which do not apply by use of the isolation procedures given in column 3.

(4)  
Perform the easiest one first to clear the trouble when two remedies present themselves.

(5)  
Perform the preliminary checks recommended by the component vendor before removing the component. For example on a questionable CSD, check drive filter and magnetic drain plug. Replace CSD and line filter and clean the cooler lines if bright chips or flakes are found on the plug.

B.  Use of "In Flight or Ground Check Analysis"
(1)  This method of trouble shooting power system faults is based on a very accurate statement of what happens in the monitoring devices when a fault occurs. If the flight log says "generator one tripped off, couldn't get back on line," this tells the ground crew nothing and it will be necessary to re-establish the cause of trouble and carefully observe the operation of the various circuit breakers, lights, meters and annunciator panel signals. If in another instance the flight log says; "Generator No. 1 control relay (GCR) and generator breaker tripped. Closed generator control relay and the generator control relay retripped. FF and UV signal on the annunciator panel," the mechanic now has a rather complete story of the fault, and by reference to Table I will find the description of the above fault under the second line. This refers him, in the last column, to paragraph 4.F.(l)-(2). This paragraph lists the trouble as "APU switch remains in contact in off position," and tells the mechanic how to isolate the trouble. This method of trouble shooting depends upon completely accurate statements of monitoring indications after a fault has occurred and any statement less than complete can be misleading.
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C.  The trouble shooting charts and procedures on the following pages are used in locating a defective component which is causing symptoms of incorrect operation of the AC generation system. The above examples of procedures may be followed from the symptom listed, noting the possible cause, and then checking the component listed opposite this cause until the difficulty is eliminated.
D.  Trouble shooting procedures cannot cover every possible fault that may develop in the system, however, the method outlined in the above procedures may be used to "shoot troubles" not listed. In addition to the above procedures for the use of annunciator signaled trouble charts, and in-flight analysis methods, the following trouble shooting routines should be followed in every instance.
2.  General Trouble Shooting Procedures
A.  No specific set of routines can be given to cover all the problems which may present themselves to anyone correcting trouble. However, certain general precautions are considered helpful in electrical trouble shooting.
B.  All checks should be started by ascertaining that 28 volt dc control power is available and that the necessary circuit breakers in these control circuits are closed, and that the circuit breakers for the generator control panels, the bus protection panel and the annunciator panel are closed. Where breakers have tripped or opened, the electrical wiring must be thoroughly checked for short circuits before assuming that the control system is in an operating condition.
CAUTION:  DO NOT REMOVE ANY GENERATOR CONTROL UNIT WITHOUT FIRST OPENING THE GENERATOR CONTROL RELAY AND GENERATOR CIRCUIT BREAKER. TO DO SO MAY DAMAGE CURRENT TRANSFORMERS BY OPENING THE SECONDARY CIRCUIT.
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