How to Test a Resistor With or Without a Multimeter

A resistor is a two-terminal passive digital part that resists, or limits, the move {of electrical} present in a circuit. It’s a vital part present in each circuit in varied sizes and styles to regulate the sign ranges, divide voltage, implement biasing, shield different digital elements within the circuit, and so forth.

Thus, if a resistor fails or goes dangerous, it will possibly result in circuit failure and render the system unusable. This DIY information will allow you to discover a dangerous resistor with out fully eradicating it from the circuit, and measure a resistor worth with or with no multimeter.


Steps to Check a Resistor With a Multimeter

When a resistor fails, it normally will get charred or burns. Because of this, it both stops conducting {the electrical} present/sign or doesn’t resist the present move. Should you assume {that a} resistor within the circuit has failed or want to check it, observe these steps.

Step 1: Change Off Energy Provide to the Circuit

Earlier than you entry or begin testing the circuit for a nasty resistor, you could unplug the system from the mains energy as this may be deadly. If a battery powers the system, take away it as it will possibly result in false positives or point out flawed values in the course of the exams.

Step 2: Get a Multimeter

To check or discover a dangerous resistor in a circuit, you want a multimeter with a resistance setting (ideally auto-ranging). If you have already got a multimeter, swap the multimeter dial to resistance mode or the setting with the Ω (ohm) image.

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If in case you have by no means used a multimeter or are a newbie, discover ways to use a multimeter earlier than you proceed.


multimeter positioned to ohm resistance mode

Additionally, test if there’s a big capacitor within the circuit and discharge it by shorting its two terminals earlier than measuring or testing the resistor. Shorting the capacitor terminals will totally discharge it and stop the multimeter from getting broken or displaying flawed values. Now you’re prepared to check the resistor in a circuit.

Step 3: Check or Measure the Resistor Worth Utilizing Multimeter

Join the multimeter probes to the resistor on the circuit that you simply assume is dangerous or appears charred or burnt. You’ll be able to contact the probes to the resistor terminals or to the soldered joints on the board to check the resistor.


Nevertheless, it’s endorsed that you simply desolder one of many resistor’s terminals from the circuit to get the correct take a look at end result and worth. After connecting the probes to the resistor terminals, test the worth on the multimeter.


measuring charred resistor value in circuit

If the resistor is okay, the multimeter will present its worth in Ω, kΩ, or MΩ. Nevertheless, if the resistor is dangerous or broken, the multimeter might show 0 or 1.

If the worth 0 is displayed, the resistor is broken, and the present can’t move by means of. If the worth is 1, the resistor is broken, permitting all present to move by means of, i.e., it’s now not resisting the present move. It’s worthwhile to change the resistor with the identical worth resistor in each instances.

To check particular person resistor values (exterior a circuit), join the multimeter probe wires to the resistor’s two terminals—it does not matter which means spherical, as resistors aren’t directional elements. Be certain that the multimeter dial is in resistance measuring mode. Then test the worth on the multimeter.


testing measuring resistor value using multimeter

Should you shouldn’t have an auto-ranging multimeter, the multimeter might show the worth 1, indicating that the resistor worth is simply too excessive to measure. In such a case, rotate the dial on the multimeter to greater resistance worth settings. If it nonetheless shows 1, the resistor might be broken and must be changed.

Equally, to test if an SMD (surface-mount system) resistor is working or not, you’ll be able to take a look at or measure SMD resistor values. Join the 2 multimeter probes to the SMD resistor terminals and test the worth on the multimeter.


measuring smd resistor value

Discovering Resistor Values With out a Multimeter

You’ll be able to’t measure a shorted or broken resistor worth utilizing a multimeter. Nevertheless, you’ll be able to learn the colour bands on the resistor to seek out its worth.

For example, if an ordinary (steel movie, carbon movie, or steel oxide movie based mostly) four-band resistor has purple, black, purple as its first three bands, its worth may be calculated as:

20 x 10² = 2,000Ω (ohms) or 2kΩ (kilohms)

SMD Resistor Values

As a substitute of coloured bands, SMD resistors have three or 4 digits written on them, which you’ll be able to interpret to calculate the resistor worth. In a three-digit SMD resistor, the third digit signifies the index/energy worth of the 10x multiplier.

For example, an SMD resistor with the 102 worth signifies 10 (first two digits) x 10² (third digit) = 1000Ω or 1kΩ.

512 = 51 x 10² = 5,100Ω or 5.1kΩ

821 = 82 x 10¹ = 820Ω or 0.820kΩ

In a four-digit SMD resistor, the fourth worth signifies the index/energy worth of the 10x multiplier. For example, 8210 = 821 x 10º = 821Ω. Equally, 8211 = 821 x 10¹ = 8,210Ω (8.21kΩ) and 8212 = 821 x 10² = 82,100Ω (82.1kΩ).


smd resistors value calculation

If there’s an R worth between the SMD resistor digits, it signifies a decimal level. For example, 1R50 or 1R5 is 1.5Ω.

As soon as you discover the resistor worth, change the broken resistor with a brand new one. You may get a brand new resistor from a close-by pastime or on-line digital part retailer and change the dangerous resistor by desoldering it after which soldering the brand new resistor. If you’re not skilled or have by no means soldered a part, discover ways to solder.

Does Changing a Unhealthy Resistor Repair the Circuit?

Not essentially. If the resistor obtained broken as a result of malfunctioning of different elements within the circuit or a excessive energy provide, you could look into the supply of the difficulty, as the brand new resistor might not survive lengthy and should require substitute quickly.

Nevertheless, it’s price a attempt. If the resistor has failed as a result of some non permanent problem, corresponding to a voltage surge, you need to use a surge protector to guard your circuits and home equipment.


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