Aircraft systems tests and operational checks should be performed under conditions as nearly operational as possible. Such tests or checks should be performed in accordance with the instructions outlined in the applicable MIM. Make the operational checks in the sequence outlined in the MIM. Any discrepancies you find when performing a step should be corrected before proceeding. The operational check and the troubleshooting charts have been coordinated so that malfunctions can be isolated in an efficient manner. If the troubleshooting aids do not list the trouble being experienced, you will have to study the system schematics and perform the operational check. Use logic and common sense in pinpointing the cause of the malfunction. The test stand to be used in performing the operational check must be capable of producing the required flow and pressure required for proper operation. Check all electrical switches and circuit breakers, as well as hydraulic selector valves, for proper position. Perform this check before applying external electrical and hydraulic power. Perform all maintenance in accordance with the MIM. Observe all maintenance

Figure 3-11.A typical electronic multimeter.

precautions and requirements for quality assurance verification.

Personnel involved in troubleshooting and per-forming operational checks should consult the records maintained in maintenance control and/or the work center register. Reference to records of previous maintenance may show a progressive deterioration of a particular system or a previous discrepancy. This procedure could be helpful in pinpointing the cause of the malfunction currently being experienced.

Since practically all systems now have some electrically controlled components, troubleshooting must also include the related electrical circuits in many instances. Although an AE is generally called upon to locate and correct electrical troubles, you should be able to check circuits for loose connections and even perform continuity checks when necessary. Therefore, a knowledge of electrical symbols and the ability to read circuit diagrams is necessary. Figure 3-4 illustrates the electrical symbols commonly found in schematic diagrams.

Loose connections are located by checking all connectors in the circuit. A connector that can be turned by hand is loose and should be tightened hand tight.

A continuity check is simply a matter of determining whether or not the circuit to the selector valve, or other electrically controlled unit, is complete. Continuity checks are made with the use of a multimeter. The name multimeter comes from MULTIPLE METER, and that is exactly what a multimeter is. It is a dc ammeter, an ac ammeter, a dc voltmeter, an ac voltmeter, and an ohmmeter, all in one package. Figures 3-10 and 3-11 show the faces of commonly used multimeters. The applicable instructions should be consulted prior to equipment operation.