TESTING OF ELECTRONIC COMPONENTS

TESTING OF ELECTRONIC COMPONENTS

AIM

 To study the testing and identification of leads of various passive and active electronic devices.

COMPONENTS AND EQUIPMENTS REQUIRED

Resistors, capacitors, inductors, transformer, diodes, transistors, multimeter etc.

THEORY

Electronic components may become faulty due to many reasons such as aging, surrounding temperature, voltage and currents more than the rated value etc. Before wiring up the circuit connections, all the electronic components should be tested essentially. The conventional methods used for measuring passive and active components described below. Digital LCR meters are available to measure inductance capacitance and resistance.

PROCEDURE

a)      TESTING OF RESISTORS 

     Keep the multimeter in ohmmeter mode.Testing a Resistor with an ohmmeter is the best, easiest and most effective way to tell whether a resistor is good or not.To set up for the check, we take the multimeter and place its probes across the leads of the resistor. The orientation doesn't matter, because resistance isn't polarized. 

b)      TESTING OF CAPACITORS

 
Capacitors should produce an infinite reading on a multimeter. Exceptions are electrolytic and very high value block capacitors. When the positive end of an electrolytic capacitor is connected to the positive probe of an analog instrument, and a negative end to a negative probe, the needle moves slightly and gradually comes back towards infinity. This is proof the capacitor is ok, and the needle's movement is charge being stored in the capacitor. (Even small capacitors get charged while testing.)
    Variable capacitors are tested by connecting an ohm-meter to them, and turning the rotor. The needle should point to infinity at all times, because any other value means the plates of the rotor and stator are touching at some point.There are digital meters that have the ability to measure capacitance, which simplifies the process. With this said, it is worth mentioning that capacitors have considerably wider tolerance than resistors, (about 20%).

c) TESTING OF TRANSFORMERS AND COILS
   
Transformers are tested by measuring the resistance of the copper wire on the primary and secondary. Since the primary has more turns than the secondary, and is wound using a thinner wire, its resistance is higher, and its value is in range of tens of ohms. Secondary resistance is lower and is in range between several ohms to several tens of ohms, where the principle of inverse relations is still in place, high power means low resistance. If the multimeter shows an infinite value, it means the coil is open. Coils can be tested in the same way as transformers – through their resistance. All principles remain the same as with transformers. Infinite resistance means an open winding


d) TESTING OF DIODES

To check an ordinary silicon diode using a digital multimeter, put the multimeter selector switch in the diode check mode. Connect the positive lead of multimeter to the anode and negative lead to cathode of the diode. If multimeter displays a voltage between 0.6 to 0.7, we can assume that the diode is healthy. This is the test for checking the forward conduction mode of diode. The displayed value is actually the potential barrier of the silicon diode and its value ranges from 0.6 to 0.7 volts depending on the temperature. 
     Now connect the positive lead of multimeter to the cathode and negative lead to the anode. If the multimeter shows an infinite reading (over range), we can assume that the diode is healthy. This is the test for checking the reverse blocking mode of the diode.

e) TESTING OF TRANSISTORS

     

1.      Keep the DMM in diode mode
2.      Connect the positive probe to one of the terminals and measure the readings by connecting to other two terminals, if we get a lower reading from both terminal then the terminal connected to positive probe is the base. Else repeat the step with switched probes.
3.      Repeat step 2 until you find a common terminal that gives lower reading when you connect to other two terminals. 
4.      Based on the probe connected to the common terminal you can identify the transistor type ie if we get the result when the common terminal is connected to positive probe then transistor is NPN otherwise it is  PNP.
5.      The terminal which showed higher reading is the emitter and lower reading is the collector.
6.      If the common terminal gives a lower reading for both positive and negative probes then the transistor is a damaged one.

RESULT

The testing of various passive and active electronic components is studied and verified the pin configurations.