Chapter 10 — SAFETY; TEST EQUIPMEMT; TEST METHODS 



MOBIZ O— 

 SIGNAL 

 INPUT g 



EXTEfiMAL 

 SYNC 

 INPUTq_ 



VERTICAL 

 SIGNAL 

 INPUT 



HORIZONTAL 

 DEFLECTION 



AMPLIFIER 



TIME BASE 



(SWEEP) 



GENERATOR 



UT 9 



VERTICAL 

 DEFLECTION 



AMPLIFIER 



TRY TO LOCATE THE TROUBLE BY OBSERVING THE 

 CIRCUIT'S FAULTY OPERATION 



I TRY TO LOCATE THE TROUBLE BY USING EYES AND NQSE |p 



20.324 

 Figure 10-4. — Block diagram of a CRT oscillo- 

 scope. 



observe signal waveforms. The latter use is par- 

 ticularly helpful, inasmuch as many technical 

 m.3nuals include (in their servicing block dia- 

 grams) waveforms at various test points. 



The oscilloscope (fig. 10-4) consists of a 

 cathode ray tube, vertical and horizontal beam 

 deflecting circuits, sawtooth voltage sweep cir- 

 cuits, and necessary power supplies. The signal 

 to be observed(asine wave, for instance)is applied 

 to the vertical deflection plates. If that were the 

 only signal applied, all you would see on the scope 

 would be a straight, vertical line. To have the 

 sweep conform to the sine wave voltage on the 

 vertical deflection plates, a sawtooth (linearly 

 increasing) voltage is applied simultaneously to 

 the horizontal deflection plates. The result is that 

 the sweep moves across the scope at a uniform 

 rate, following the fluctuations of the signal applied 

 to the vertical plates. When the sawtooth signal 

 reaches its cutoff point, the sweep returns rapidly 

 to its starting point, to await the next sawtooth 

 signal. The measurement of frequency, calibra- 

 tion, and other special situations requires the use 

 of a synchroscope, which is an oscilloscope with 

 special circuits added, such as sweep triggers and 

 miirker generators. The sweep commences only 

 whan a signal is received. Oscilloscopes and syn- 

 chroscopes are explained in detail in Handbook of 

 Test M etho ds and Practices , and Basic Elec - 

 tronics . 



TEST METHODS 



Whenever a piece of sonar equipment breaks 

 down, it may be your job to locate the trouble and 

 restore the faulty circuit to its proper operating 



12.259(71) 

 Figure 10-5. — Troubleshooting procedure. 



condition. The means by which you will find the 

 faulty component is called troubleshooting, which 

 consists of logical testing methods. Troubleshoot- 

 ing aids you will use are troubleshooting chaxts, 

 servicing diagrams, and voltage and resistance 

 charts. 



Troubleshooting chai-ts list various equipment 

 malfunctions, their probable cause, and the neces- 

 sary corrective action. Servicing diagrams show 

 test points, desired waveforms, proper voltages, 

 and other related servicing information. Voltage 

 and resistance charts show the normal voltage and 

 resistance values at the pins of connectors and tube 

 sockets. 



Although much of the equipment you are 

 required to maintain is quite complex, and you may 

 feel that it is beyond your capability to keep it 

 operative, the job usually becomes much easier if 

 it is first broken up into successive, logical steps. 

 Figure 10-5 shows a general troubleshooting pro- 

 cedure. Steps 1 through 5 aa'e to be followed in 

 locating the trouble. Steps 6 and 7 are carried out 

 in making repairs. Sometimes steps 2, 3, 4, and 5 

 may be eliminated, but never steps 6 and 7. 



TERMINAL DESIGNATIONS 



When carrying out your troubleshooting pro- 

 cedures, you will find that many test points are 

 located on terminal boards. Wiring diagrams, 

 which aid you in tracing a circuit from one unit to 

 another, indicate the terminal connections of each 

 circuit in each unit. You must understand, there- 

 fore the system used for m.arking terminal boards 



159 



