1. Win a Broadcaster or one of 3 Teles! The annual Supporting Member Giveaway is on. To enter Click Here. To see all the prizes and full details Click Here. To view the thread about the giveaway Click Here.

Using your meter to troubleshoot guitar problems.

Discussion in 'Just Pickups' started by dsutton24, Sep 5, 2016.

  1. dsutton24

    dsutton24 Doctor of Teleocity Ad Free Member

    Posts:
    10,229
    Joined:
    Dec 29, 2010
    Location:
    Illinois
    Well, it happened. You just wired your new pickups and wouldn't you just know it, they don't work!

    Lest anyone get the wrong idea, it happens to all of us, and that's the truth. The following is aimed at the guy who rarely tackles a electronic mod of any kind. He's just spent a bunch of money, and sweated bullets over soldering. He's wired it exactly* like the drawing, and it doesn't work. He's got a meter laying around somewhere, or is willing to run out and get one.

    Problem is, what is the meter telling him?

    First things first...

    This will be Telecaster specific, and it assumes you're using a metal control plate, and are doing a three way or four way switch. There are just too many variables to be able to account for all guitars and all schemes. But, anything you learn here can be applied to most guitars. Amps are another subject altogether, don't breeze through this and then tie into your Super Six.

    *Chances are you didn't wire it exactly like the drawing. If you've stressed over the project at all, you'd be amazed at how easy it is to overlook a simple wiring mistake. Probably fifty percent of troubleshooting threads start with a wiring error. The next most likely problem is poor soldering. If you're starting with new components, it's possible something arrived on your bench bad, but that's a rarity, probably five percent or so. This implies that 95% of the time it's you, not it. That's not an insult, that's just the way learning works. And you're not alone. The only time you'll see troubleshooting threads is when there's trouble. The guys who successfully wired their new project have gone right to the NGD thread.

    The first thing to do is to post a thread here or in Tele Technical. The information we need is simple:

    What did you do?
    What pickups are you using?
    What wiring diagram are you using (post it in your thread)?
    What exactly is going on?
    And most importantly, a good clear, close picture of the back of your control plate.



    The 'What did you do' is very important. Did you start with a working guitar, mod it, and run into trouble? What parts did you replace? Is it a new guitar with no track record? As simple as it sounds, knowing this helps a lot.

    Details are important. Tap on each pickup, and do it in each switch position. Do you hear the tap through your amp? Is the guitar quiet? If it buzzes, when does it buzz, and what can you do to make it stop buzzing? Have you tried more than one amp, and more than one cable?

    The photo is important. A good drawing and good components are essential, but nobody can tell how you interpreted the drawing. Don't be worried about how it looks, no matter who you are I'll guarantee we've seen worse.

    Most of the time, if somebody can see your wiring, and understand your problem, an answer will come along pretty quickly that will point you in the right direction. An awful lot of people here have been in your shoes at some point, and will be able to help you along.
     
    Last edited: Sep 5, 2016
  2. dsutton24

    dsutton24 Doctor of Teleocity Ad Free Member

    Posts:
    10,229
    Joined:
    Dec 29, 2010
    Location:
    Illinois
    Okay, we've looked your project over, and nobody has seen an obvious mistake. There's probably been a fair amount of back-and-forth. Now somebody wants you to get your meter out and make some measurements...

    Gulp!

    Don't worry, it's not difficult. It just requires you to be a little methodical about things.

    Let's start with your meter.

    I've used a CenTech digital meter for the following. It's cheap, I bought mine for $7.00 at Harbor Freight. This meter seems to be pretty typical of the cheap meters out there, so it's a good start. If you're shopping for a meter, pick up a bag of clip leads while you're there. They're amazingly handy things to have.

    First, turn the thing on:
    [​IMG]

    Plug your black lead into the jack marked 'COM', and the red lead into the jack marked VΩmA. If you're like most of us your leads will stay there almost all the time.

    Connect a red clip lead to the red test probe, and a black one to the black test probe. You don't ever want to touch the metal tips of your test leads with your fingers when making measurements. If you're making voltage measurements, the reasons are probably pretty obvious. But, if you're making resistance measurements your skin resistance can cause errors that can be misleading. Use your clip leads.

    Now, select the 20K resistance range, this is important. With the clip leads not touching each other, take note of what the display reads:

    [​IMG]

    The display will read something cryptic, in this case 1<blank><dot><blank>. Different meters do this differently. It essentially means that the circuit is open. Use the term 'open' to describe this condition, not 'nothing', 'no change', or the like. Since we don't know how every meter acts, 'nothing' means... well, nothing, as in no useful data. Any time you report a resistance reading, be sure to note the range, and what the display reads. So, this would be 'open on the 20K range'.

    Now, short your clip leads together and note the display:

    [​IMG]

    It should read something close to zero. It may read a very small resistance, this is normal. Again, when you report a resistance reading, be sure to note the range, and what the display reads. In this case you'd report it as '0.0 on the 20K range'. The blue arrows point out two important details, the resistance range your meter is set to, and watch that danged decimal point.

    Go through this exercise every time you turn on the meter. This insures that your meter and test leads are good, and you're familiar with the operation of the meter.

    Oh, blah, blah, blah, all this futzing around isn't really necessary, is it? Yes, it is. Here's why. Let's hook our meter up to an unknown resistance:

    [​IMG]

    It looks like it's open, right? Hmmm... Let's bump up to the 200K range:

    [​IMG]

    Still open? Let's go to the 2000K Range:

    [​IMG]

    Oh, something changed, but what does it mean? 685 on the 2000K range, the resistor is a 685KΩ.

    This is why knowing what range you're on is very important. 685 'what'? 6.8KΩ is a pretty normal resistance for a single coil pickup. 685KΩ is a hundred times what a typical pickup will measure, 685Ω is very low, it's probably a bad pickup or something going on with your volume control.

    So, report the reading on the meter, and the range.

    If you're measuring an unknown resistance, start with the highest resistance range, and then work your way down. You'll get the best accuracy if you use the range that is the closest but higher than the resistance you're measuring. Since I know from experience that most pickups will fall below 20K, I started with the 20K range. That's a shortcut that can lead to trouble, however, as our 685K resistor illustrates.
     
    Last edited: Sep 5, 2016
    boredguy6060 likes this.
  3. dsutton24

    dsutton24 Doctor of Teleocity Ad Free Member

    Posts:
    10,229
    Joined:
    Dec 29, 2010
    Location:
    Illinois
    Okay, let's measure some stuff.

    We'll start with some simple checks of our grounds.

    Note: Not all hum or buzz problems are the result of a bad ground. Noise problems can just as easily be something going on in your signal path. Repeat that until it's second nature. As important as grounds are to both safety and signal purity, they're not the only answer. Also remember that a bad ground somewhere will cause no sound or low sound conditions.

    Set your meter to the 200 resistance scale.

    Plug a known good cable into your guitar. Turn all the knobs fully clockwise. Why? Bear with me, it'll become clear. Clip the black clip lead to the sleeve of the unused plug, and set it all on something non-conductive. Your meter should indicate an open. Clip your red clip lead to the control plate:

    [​IMG]

    Now, what does the meter say?

    [​IMG]

    02.0 on the 200 scale means that the resistance between the shield of the cable to the control plate is 2Ω, not bad. Anything under 5Ω or so is good. A high resistance here will be from a bad cable, a bad solder joint either on the jack or the back of the volume pot where that ground connects, or just a missing wire. Don't go on until this is fixed.

    Next, the neck pickup cover. I held the clip lead against the cover, and held it in place with a piece of paper to insulate it from the strings.

    [​IMG]

    01.2 on the 200 range means 1.2Ω, that's good.

    Let's say your resistance from the plug sleeve to the pickup cover is very high, what does that mean? It means that your pickup cover isn't grounded. That will be normal if the cover is plastic. But, usually high resistance between the sleeve and the cover will indicate trouble. You'll most often see this when you're doing a 4 way mod and forgot to ground your cover, or you have a bad solder joint.

    The most important last, the bridge ground:

    [​IMG]

    Yep, that's a good ground. 0.26 on the 200 range means the resistance from the sleeve to the bridge is 2.6Ω.

    But what if it isn't?

    [​IMG]

    171.4 on the 200 range makes it 171.4Ω, way too high. What happened?

    Some bridges get grounded through the metal baseplate of the bridge pickup:
    [​IMG]

    This works fine if the pickup has a metal baseplate, many don't. This type of ground will fail over time from the corrosion that happens from blood, sweat and beer.

    Another common bridge ground is done by trapping a ground lug on a pickup mounting screw:

    [​IMG]

    This is the cheesiest way to do this. It works fine as long as you've got good metal to metal contact, and everything is bright and shiny.

    The third common way to ground a Telecaster bridge is to trap a ground wire under the bridge:

    [​IMG]

    This method usually gives the best long-term bridge ground. There are two potential pitfalls to this method. One, over time the bare wire can sink into the body, and the bridge ground will fail. When this happen, just reposition the wire to a new spot. Also, if you get too carried away with the exposed wire the bridge will not lay flat against the body. Use enough wire to get good contact, and it helps to fan out the strands.

    Remember, also, that all your shields must be bonded together and grounded. If they aren't they won't shield, and in fact they can become a new source of hum that is hard to get rid of. With your black clip lead still attached to the sleeve of the plug, touch the red clip lead to each shield. You may see some significant resistance if you're testing shielding paint, maybe on the order of a hundred ohms or so. That's normal.

    If you've gotten this far, chances are good your ground path is all good.

    What about the relationship between grounding and hum? Single coil pickups can pick up hum, it's in their nature. If touching the strings makes the hum go away (or at least diminish it greatly), the bridge is grounded and the guitar ground circuit is wired correctly.
     
    Last edited: Sep 5, 2016
    boredguy6060 likes this.
  4. troy2003

    troy2003 Friend of Leo's

    Posts:
    2,317
    Joined:
    Mar 30, 2010
    Location:
    ?
    Great thread. And will be extremely helpful to people. Thanks for sharing
     
  5. dsutton24

    dsutton24 Doctor of Teleocity Ad Free Member

    Posts:
    10,229
    Joined:
    Dec 29, 2010
    Location:
    Illinois
    Now, on to the signal side of things.

    Set your meter to the 20K resistance range.

    Plug a known good cable into your guitar. Turn all the knobs fully clockwise. Clip the black clip lead to the sleeve of the unused plug, and the red clip lead to the tip of the plug. Put your selector in the 'Bridge Only' position:

    [​IMG]

    7.27 on the 20K range means 7.27KΩ, that's a pretty normal resistance for a single coil pickup. In general anything between 5K and 8K will be normal. This is why knowing what pickups you're using is important, they can vary quite a bit.

    Now, let's go to the "Neck Only' position:

    [​IMG]

    7.58 on the 20K range, that's 7.58KΩ. Again, that indicates that all is probably well with the pickup, the switch and the wiring.

    Now, the 'Neck + Bridge' positon:

    [​IMG]

    3.82 on the 20K range, that's 3.82KΩ. Whoa... what happened here? That's normal. In Telecasters the B+N positon usually puts the pickups in parallel, and any time you put resistances in parallel, the resistance of the circuit will be less than the smallest resistance. In others like the B+N in series position of a 4-Way Telecaster, or some (maybe all) Danos, the B+N positon resistance you read will be the sum of the resistances of both pickups.

    A couple of things to keep in mind.

    If you've got two very different pickups, say a single coil plus a humbucker, that's when it's important to know what the resistance of the pickup is before you start troubleshooting. You may find one pickup is half the resistance of the other, and both in parallel is very low. That may be normal. Also, if you're mixing Humbuckers and single coils you may also be adding resistance somewhere to help balance them. Post your drawing, it's essential if you need help with something out of the ordinary.

    Several times during the preceding I directed you you turn all controls to max clockwise. Why is this important? You're dealing with a circuit that has one or two pickups, a tone control, and a volume control, and they all have the potential of interacting. If your tone control is wired correctly, it will have no impact on the resistance you read at your plug. If, however, you turn the tone control and things start changing, then you know your tone control needs attention.

    What if you don't max your volume control? Let's try it:

    [​IMG]

    With the volume turned down, you're seeing 0.14 on the 20 K range, that's 140Ω. You were expecting something more like 7K. Before you get all excited, crank the volume control. It may be wired backward, or just turned down.

    There are some basics to build on. Someday when it's raining out and the Bears are loosing, get out a working guitar and hook up your meter and experiment with it. Familiarity will certainly help when things go wrong and you need to troubleshoot.
     
    Last edited: Sep 5, 2016
    boredguy6060 likes this.
  6. dsutton24

    dsutton24 Doctor of Teleocity Ad Free Member

    Posts:
    10,229
    Joined:
    Dec 29, 2010
    Location:
    Illinois
    Now, wrapping up.

    I started a thread few days ago asking what meters are being used here. The Harbor Freight / CenTech showed up over and over. It's also pretty similar to many others functionally, so it seemed the perfect meter for this thread. Many thanks to all who answered.

    This isn't meant to be an all-inclusive guitar troubleshooting manual. It will give you a start on using your meter, and if you need help troubleshooting a problem it may give you some insight into why you're being asked soooo many stinkin' questions. There are just too many variables to take into account. A thorough understanding of your meter, some techniques, and how the circuit you're working on should work goes a long way toward success.

    The CenTech meter is usable, no doubt. One thing I noticed is that the range selector is a little flabby in the way it detents into positon. If you get measurements that don't make any sense, try flipping it into the next higher range. If it settles down, go back into the range you want to use.

    If you're going to do a lot of metering, do yourself a big favor and buy a good autoranging meter. I like Fluke, there are plenty of other good ones. Bought new they can run anywhere from a hundred bucks and up. Waaaaay up. A basic meter is all you need, but if you're going to work on amps or pickups a meter that has the ability to measure capacitance is a definite plus. I buy a lot of used Flukes in pawn shops, the last one was $27.00. In general, if a Fluke lights up it will function just fine. Turn it on, and check the line voltage in the pawn shop. Turn it to resistance, and short he leads together and give everything a good shake. If it stays under 1Ω, you're almost guaranteed to be good to go.

    If you're using an auto-ranging meter (like the Fluke) it's vitally important to note what the display says carefully. It will list a voltage, say 128. But, 128 what? 128 mv, 128 volts, they're very different things.

    When doing voltage measurements, set your meter to the proper range, then measure a known voltage. Ideally this voltage should be higher than you are expecting to work on, but sometimes that's impractical. If nothing else, plug your test leads into a wall outlet. 120 volts more or less, right? Do your measuring. If something doesn't seem right, check your wall outlet again, this confirms your meter and leads are still working, and that the meter is setup correctly.

    Keep a handful of resistors on hand that you know the values of. Say you're working on a single coil project, and things just don't add up. Whip out your trusty 6.8KΩ resistor and measure it. If it's right, you know your meter and brain are working together like they should. Likewise, a 9v battery will keep you honest if d.c voltage is a problem.

    No matter the meter, keep it clean. If it starts acting weird replace the battery before you panic.

    DC resistance is not a good indicator of how a pickup will sound. It can be part of a useful troubleshooting technique, though.

    Here are some typical pickup / switch positon relationships that might be useful. Note the variation in DC resistance of pickups of similar type:[​IMG]
     
    Last edited: Sep 5, 2016
    Rob DiStefano and boredguy6060 like this.
  7. Steve 78

    Steve 78 Friend of Leo's Silver Supporter

    Age:
    43
    Posts:
    2,563
    Joined:
    Oct 27, 2015
    Location:
    Melbourne, Austraila
    Great thread. Thanks for posting.
     
  8. Andy B

    Andy B Friend of Leo's Silver Supporter

    Posts:
    2,475
    Joined:
    Mar 16, 2003
    Location:
    Castle Rock, Colorado
    Good thread with lots of useful info. For many years I have used a guitar cable with a 1/4" plug on one end & a pair of banana plugs on the other end to check & troubleshoot guitars. Works better than all the jumpers IMO.
     
  9. blowtorch

    blowtorch Telefied Ad Free Member

    Posts:
    37,924
    Joined:
    May 2, 2003
    Location:
    Wisco
    thank you for this, as I have a meter and not much of a clue, and I bet neither my dad, who has electrical experience, or my cousin, who is a mechanic and works with multimeters often, would understand the guitar-specific uses of it enough to advise me in that context
     
  10. boredguy6060

    boredguy6060 Poster Extraordinaire

    Posts:
    5,666
    Joined:
    Mar 28, 2012
    Location:
    Sou Cal
    Thanks for the info.
     
  11. Thin69

    Thin69 Friend of Leo's

    Posts:
    2,915
    Joined:
    Oct 28, 2009
    Location:
    Galveston, TX
    Nice of you to take the time to develop this comprehensive thread on how to use a meter. Great job!
     
  12. richiek65

    richiek65 Friend of Leo's

    Posts:
    4,699
    Joined:
    Dec 26, 2012
    Location:
    Sydney NSW Australia
    Brilliant thread! I'm clueless on electronics, despite my electrician father explaining many times how to use a multi meter.. I've tried some pickup installs with mixed results, i may now have some more clues on how to progress.. cheers!
     
  13. PDuster

    PDuster TDPRI Member

    Age:
    42
    Posts:
    26
    Joined:
    Apr 22, 2017
    Location:
    Nowheresville
    Wow. Just found this. Invaluable tutorial for electrical dumb-asses like me who want to do their own wiring. Thanks for your time and effort in writing this tome.
     
  14. mannydingo

    mannydingo TDPRI Member

    Posts:
    19
    Joined:
    Aug 8, 2009
    Location:
    Miami
    Excellent. I have that same Harbor Freight/CenTech unit. I just bought a used guitar for 10 bucks and makes no sound. Where do I place the dial on the meter to test the 3 way switch? What do I look for? I read online to use the continuity option on the dial. One lead to center and the other lead to either of the side leads of switch, then the other. I'm supposed to hear a tone. Does this meter produce a tone? Should I get a reading? Should the wires be unsoldered from the switch first?
     
  15. mannydingo

    mannydingo TDPRI Member

    Posts:
    19
    Joined:
    Aug 8, 2009
    Location:
    Miami
    Remove blank post
     
    Last edited: Jul 8, 2017
  16. JK202

    JK202 TDPRI Member

    Age:
    66
    Posts:
    66
    Joined:
    Feb 1, 2019
    Location:
    Arlington, Virginia USA
    Just saw this.. thank you very much for this great info! I think I can do this :)

    Cheers!
     
  17. rigatele

    rigatele Tele-Afflicted

    Posts:
    1,535
    Joined:
    Apr 20, 2014
    Location:
    Canada
    Believe it or not, it's also possible to measure the volume pot value from the jack. I lost and then found and then lost the envelope with the math on it. Basically you take the reading at max volume, and then the highest reading that you get when the volume pot is run up and down, plug it into a magic formula and voila! Instant pot value, e.g. 250k or 500k and so on.
     
  18. Rob DiStefano

    Rob DiStefano Doctor of Teleocity Vendor Member

    Age:
    75
    Posts:
    10,297
    Joined:
    Mar 3, 2003
    Location:
    NJ via TX
    good stuff, indeed. thumbsup.gif
     
  19. Modman68

    Modman68 Tele-Holic

    Posts:
    875
    Joined:
    Mar 27, 2011
    Location:
    La mesa
    This thread should get stickied. Thanks Dsutton!


    Sent from my iPhone using Tapatalk
     
IMPORTANT: Treat everyone here with respect, no matter how difficult!
No sex, drug, political, religion or hate discussion permitted here.