Before testing resistors please make sure that you take it out from the circuit so that you will have the most effective way of testing.
RESISTOR COLOR CODING
Resistor color coding is one of the basic things that we need to know about resistor. If you take a look on a resistor - you can see some color lines on its body. Those lines of colors correspond to its ohmic value and tolerance. Below on fig1 are the lines of colors that you will find in resistor and its value.
fig1. Resistor Color Coding
Pretend that you have a resistor now and let say that the colors around it are Red, Black, Red, Gold. The first two colors, Red and Black, are first and second significant numbers, the third color, red, is multiplier and the last color, gold, is tolerance. Based on fig1, the value of those color are Red = 2, Black = 0, Red = 100 and Gold = 5%. To get the ohmic value we need to combine the value of first and second color then multiply it with third color.
20 x 100 = 2000 or 2K ohms
To get the ohmic range, we need to get the 5% of 2000 or the tolerance value.
2000 x .05 = 100
After getting the tolerance value, add the tolerance value to ohmic value for maximum range and for minimum range subtract the tolerance value from ohmic value.
Max: 2000 + 100 = 2100 ohms
Minimum: 2000 - 100 = 1900 ohms
Range: 1900 to 2100 ohms
This color coding is very important in testing resistor because we will based our test on the computed value specially if we are testing its reliability. If the measured value is outside the ohmic range, your resistor is bad and should be change.
Another way of testing the resistor is checking its continuity. Always remember that a good resistor when measured will always give correct resistance value. If the needle of you multimeter does not deflect at all it only means that you have a bad resistor.
fig2 - Indication of bad resistor.
Meter needle does not deflect at all and remain stationary in infinity position.
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