Content

• Steps
• What do you need

Resistors regulate the current flowing through an electrical circuit. Resistors are the resistance or impedance in an electrical circuit that reduces the amount of current passing through it. These resistors are used to regulate the signal and to protect electronic devices from too high a current. To perform these functions, the resistors must be of suitable resistance and must be in good working order. This article describes how to test the health of a resistor.

Steps

1. 1 Disconnect the power supply from the circuit containing the resistor.
2. 2 Disconnect the resistor from the circuit. Measuring the resistance of a resistor that is not disconnected from the circuit will give incorrect results, since it will also contain the resistance of part of that circuit.
   • Disconnect one pin of the resistor from the circuit. It doesn't matter which of the two contacts you disconnect. To disconnect the resistor, simply pull it out. If it is soldered, melt the solder with a soldering iron and remove the resistor with tweezers. A soldering iron can be purchased at an electrical store or hardware store.
3. 3 Examine the resistor. If the resistor is blackened or charred, it is most likely damaged by too much current. In this case, the resistor must be replaced.
4. 4 Determine the resistance of the resistor. The resistance must be printed on the resistor case. On small resistors, the resistance is indicated by colored stripes.
   • Determine the tolerance for resistance. No resistor has exactly the same resistance as indicated on it. The tolerance shows how the specified resistance value can change. For example, with a resistor of 1.000 ohms with 10 percent of the permissible deviation, the value of at least 900 ohms and not higher than 1.100 ohms will be considered within the normal range.
5. 5 Prepare a DMM to measure resistance. You can get a digital multimeter at an electrical or hardware store.
   • Make sure that the multimeter is working properly and its batteries are not depleted.
   • Set the scale of the multimeter so that its maximum value is not much higher than the resistance of the resistor. For example, if you want to check the resistance of a resistor marked with a value of 840 ohms, and the scale of the multimeter changes 10 times, set the measuring range to 1,000 ohms.
6. 6 Measure the resistance. Connect the 2 probes of the multimeter to the 2 pins of the resistor. The resistors have no polarity, so the order of connection does not matter.
7. 7 Determine the resistance of the resistor. Look at the reading on the multimeter. When measuring the resistance of the resistor, take into account its permissible deviation.
8. 8 Connect a good resistor to the circuit. Plug the resistor back into the circuit if you just removed it before. If you soldered the resistor by melting its contacts, solder it into the circuit.
9. 9 Replace the defective resistor. If the resistor shows inappropriate resistance, discard it. New resistors can be purchased at your local electrical store.

What do you need

• Digital multimeter
• Electric soldering iron
• Pointed pliers