How to Back Probe with a Multimeter

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When you are doing electronic work, you may need to find out what is connected to a wire. Usually, multimeters don’t do this, and you need to do it the old-fashioned way with a back probe. If you are new to electronics and have no idea what back probing is, you probably should start here.

What Is Back Probing?

Back probing is when you test a component by taking the measurement leads from the multimeter and plugging them into the components’ leads. This technique is normally used to test components that are too small to probe or components that you cannot access the leads on.

Back probing is a fancy term for connecting your multimeter leads into an electrical component so that instead of using them to measure voltage, or current, or resistance, you are using them to control the component. This is a great technique to use when you need to control an electrical device without having to add a microcontroller or other type of fancy electronics.

For instance, say you want to control the output of a motor with a platform, but you don’t want to add all the extra hardware required to do that. That’s where back probing comes in.

Back probing is an important skill to have when using a multimeter. The skill itself is very straightforward: simply attach your multimeter leads to the leads of the component being tested. The problem arises when people try to do this with a regular, cheap $5 multimeter they bought from a thrift store.

These multimeters are typically very inaccurate, and some of the cheaper ones even have a tendency to lose connections over time, even when used on a breadboard. For this reason, it is worth it to spend the extra money to get a quality multimeter that will last you a lifetime.

Knowing its Purpose

Back probing is a method of testing on a printed circuit board (PCB), where a component is tested using its connection to another component on the PCB rather than the component’s pins. This is useful when the component itself is not accessible, for example, because it is buried inside a hole in the PCB or if it is a surface mount component that is covered by another component.

If you need to test the component, you have to remove the second component to access the component which you want to test.  If you can test the component without removing the second component, you have back probed to save time and effort.

Back Probing with Multimeter

Back probing is a method of measuring voltage using one of your multimeter leads as a test probe. It is mainly used for probing voltage traces that are too narrow or too close to other components to fit regular test probes.

It is also useful if you want to measure the voltage of a component that has no test points or if you want to measure the voltage of a circuit before soldering it together.

Back probing is a technique that is used to determine a component’s value. To do this, you need to: 

  • Connect a resistor to the component of interest, and then connect the other end of the resistor to the multimeter’s positive and negative leads. 
  • As you slowly increase the voltage on the multimeter, you read the value of the resistor that is connected to the component. 
  • The resistor’s value is then used to calculate the component’s value. 
  • This process is used to gain access to hidden components and is often used on integrated circuits and transistors.

Also, part of back probing; always strip the wires before you back probe. There are three ways to do this. 

  1. Run a wire down the inside of the wire to the end. Strip a small amount of the wire and attach it to the end (make sure that the wire is the correct width for use with the multimeter). 
  2. Use a rotary cutter to cut a slit in the insulation. Then strip some of the wire and poke it through the slit. 
  3. Use wire strippers to cut a slit in the insulation. Then strip some of the wire and poke it through the slit.

Make sure that you unplug the device BEFORE starting to back probe!! If you don’t, you risk damaging the device, which could then damage your multimeter.

Make sure you turn the multimeter off before plugging the device back in. Also, make sure you aren’t back probing any pins that are live (i.e., 3.3V). Also, make sure you don’t connect the probe to the end of the wire. That can damage the device too.

Why Do You Need To Back Probe Using This Device?

Let’s face it. You probably don’t need to back probe with a multimeter unless you’re in the electronics field or building your own circuits.

Even then, you may not need to, or we’d probably all still be using computer punch cards. If you’re just starting to learn electronics, it can be confusing to figure out how to back probe with a multimeter. Fortunately, it’s not as hard as you might think. The key to back probing with a multimeter is knowing when to do it and when not to do it. 

But why do you need to? Well, back probing is a way to check components, wires, and pins on a circuit board without using a soldering iron. This saves you time, and when you’re working with intricate circuit boards and small pins, it’s a godsend.

It can also be used to check components on cables. This skill can be used for many things, but the main use is to check the pins on a circuit board.

Other Things To Remember

A back probe is a type of test lead that is used for probing a circuit or component that is behind or underneath something. As in, if you wanted to test a component that was under a chip, or was on another board, or was underneath a shield, you would use a back probe.

Back probing is great because it allows you to test tricky circuits without removing the cover or picking or rerouting anything. The downside is that back probing can be a bit tricky to learn and requires that you have the right equipment (a back probe set).

The multimeter has an intimidating look, with a lot of buttons, lights, and dials. But you can improve your chances of proper back probing if you remember to do a few things. 

Measure twice, cut once. You should read the multimeter before probing and not ask yourself what it says once you’ve already run the test probe through the circuit. Always think before you act; back probing can be dangerous if done incorrectly.

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