Multimeter For Guitar Electronics
Guitar electronics can be a daunting subject for a beginner, but it doesn’t have to be a living hell. In this article I’ll show you how easy it is to use a multimeter on guitar electronics. You don’t need any previous experience or knowledge of electronics theory, just your multimeter, guitar, and brain. And an instrument cable.
A multimeter measures voltage or resistance setting in an electric circuit which can then be used to test components like pot values or pickup coil resistance.
When the tone of electric guitars isn’t right, there are many possible culprits: a change in the pickups or their placement could make a big difference, a switch may not have been installed correctly, and faulty wiring is always a possibility. But no matter what the problem might be, one thing that will never hurt is using a multimeter to check the continuity of electrical components.
With all the different components and connections, it can be hard to tell if a problem is coming from the guitar pickups or simply loose wires. In this blog post, we’ll talk about how you can use a multimeter to test your guitar’s electronics for problems with wires and other issues. We’ll also go over some basic troubleshooting tips that will help you identify what might have gone wrong with your instrument so that you can fix it yourself!
For some quick basics, in a guitar circuit, every component needs to be grounded. They don’t need to be grounded in the same place because all of the grounds will ultimately terminate at the output jack.
An electric guitar has a hot and a ground. These start at the guitar pickups, run separately through the switch and control pots, meet at the output jack, and flow to the amp. If the hot and ground make contact in the guitar, a short occurs and kills the signal before it hits the output jack.
A zero value returned while you test continuity means the connection is broken. This can look different based on your multimeter: 0, 0.0000, 0l, etc. When something has a short, that means there’s no resistance between endpoints.
Your multimeter can be used to measure resistance in pickups and to perform simple tests to see if a pickup is broken.
To test pickups while they are still installed in your guitar, plug a cable into your guitar . Place the black test probe on the cable sleeve. Touch the red test probe to the tip of the cable (hot). It actually doesn’t matter which probe goes where, but I’m going to try to remain consistent.
Set your multimeter to the 20K ohm setting (the unit of resistance). Set all tone and volume controls to max. Use the switch to select the pickup you want to test. This will display the DC resistance reading for the pickup.
This value, however, is not the exact reading. Removing the pickup from the guitar will provide a slightly more accurate value, but with this test you know the pickup is functioning correctly.
The value you’re looking for should be listed in the documentation that came with the pickup, or you can find it online. The value on the multimeter should be close to the listed value.
To test a loose pickup with vintage braided shield, the braid itself is the ground, and the hot is the internal wire. If you can’t see the internal wire, use cable strippers to expose a small length. Touch the black probe to the braid and touch the red probe to the hot wire.
For a loose two lead pickup, the ground is likely a bare wire, so touch the black test probe to this and attach the red probe to the remaining (hot) lead.
Loose single coil pickups are simple. Just touch each probe to one of the leads.
For a four conductor loose pickup, you will need to look at the pickup manufacturer’s specs to determine which color lead does what. There will be two leads that you don’t need. Tape these two together to get them out of the way. Touch black to the ground and red to hot.
You can also test each humbucker coil individually. Cut the expected resistance value in half and check the two leads attached to each coil. Again, you’ll need to check the manufacturer’s information to find the correct leads.
As a general guide, vintage humbuckers are usually around 8K, and extremely hot humbuckers can go over 20K. Single coils are usually around 6K for vintage to over 15K for high output. Exceptions exist, of course.
Mapping a Switch
Even with a wiring diagram, configuring a switch correctly can be a nightmare. Thankfully your multimeter can assist with mapping the switch. Set the multimeter to the continuity setting (the sound wave icon) so you can hear an audible solid tone when a circuit is closed.
Depending on what kind of switch you’re using, you may want to draw a diagram of the connections to avoid confusion.
Move the switch to bridge position. Touch a probe to the first lug and the other probe to the bridge. You should hear the continuity beep and see a value displaying on the multimeter.
If so, mark down that this lug is tied to bridge position. Check remaining lugs until you find the second lug for bridge position. You will then have located the input and output for this position.
Continue testing the remaining positions and complete your diagram.
Testing a Guitar Cable
Set the multimeter to the continuity setting. Touch each probe to a guitar cable tip for a few seconds. If you hear the beep, there’s a connection.
Lightly bend the cable and throw it around a bit. This is a way to test for a short. Test continuity again. To test the ground, move the probes to the cable shafts and listen for the solid tone.
Touch the both probes to the same end of the cable, one on the tip and one on the shaft. You do not want to hear a beep here. If you do, you may have a short.
Cables go bad all the time, so if you’re hearing no beeps or intermittent beeps, it’s likely time for a replacement.
Testing an Output Jack
Output jacks on guitars with passive pickups have one lug for primary lead and one lug for ground. Output jacks on guitars with active pickups have three lugs: the tip is primary lead, the sleeve is a battery control that turns the battery on when a cable is plugged-in, and there is an added ground.
To test where the battery switch is on a TRS (active pickup) jack, set your multimeter to test for continuity. Plug the cable into the output jack. Touch a probe to the exposed tip of the cable. Touch the other probe to one of the lugs on the output jack. Find the lug that causes the continuity feature beep. This is where the pickup lead connects.
With the plug still inserted, keep one probe on the guitar cable tip and touch another lug with the second probe. There should not be a beep. Keep the probe on this lug and move the first probe from the tip to the shaft. This should produce a beep. This identifies the lug to be used as a battery switch.
Considering how insanely over-the-top your pedal board is, you should try using a power supply instead of batteries. Guitars with active pickups also use 9-volt batteries, so I suppose I will continue with the article.
Set the multimeter to the DC V setting. Touch the red test probe to the plus (+) battery terminal and black to the minus (-) terminal. You should read the battery’s appropriate voltage range on the multimeter. If you’re testing a 9-volt and the number is under 9, the battery is running out of juice.
You can use this procedure to test just about any type of disc battery or normal battery.
Testing Guitar Potentiometers
Before starting, make sure you know the value of the pot you’re testing (250K, 500K, etc.). Set your multimeter to this value in ohms (or as close as you can get).
Touch one probe to ground and one probe to lug 2 to check value. Volume should be at max. You should see a reading in the general range of the pot’s value.
Turn the knob and make sure that value goes down to zero. Turn the knob to the halfway point. The reading will be about half of maximum value if you have a linear pot, and much less than half if you have a logarithmic pot. See this article on potentiometers for more information on these designations.
If the tone pot doesn’t work, it’s usually a ground issue. Make sure tone pot chassis is grounded. You can run ground wires from the volume pot to the tone pot.
Wow, that was a lot of information to take in.
A multimeter is a handy tool for any guitar player. With it you can test electronics and find out what’s wrong with your instrument or pick up some tricks of the trade so that next time you have an issue, you know the best way to troubleshoot before calling in a professional.
We have gone through the different settings available on a digital multimeter, how to check for continuity, how to check for shorts, and how to make sure all components are grounded. We also discussed some testing ideas like testing potentiometers, checking pickups and finding resistance, mapping switches, and testing batteries and cables.
If this sounds like something you want to take on yourself, check out the store page featuring a list of all the tools that will help make testing easier.