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MAKE Asks: is a weekly column where we ask you, our readers, for responses to maker-related questions. We hope the column sparks interesting conversation and is a way for us to get to know more about each other.

This week’s question: Finding the gremlin in an electronics prototype can be a maddening endeavour. From your experience, what’s something from left-field you find yourself checking when trying to troubleshoot an electronics project?

I once set up an XBee and had indicator lights glowing, but no functionality. After combing through my code and breadboard connections again and again I finally found the problem. There was a cold solder joint on the power pin of the breakout unit. It was giving only a small amount of power to the XBee — just enough to light the LEDs, but not enough to make the XBee work. Since then I’ve added a solder joint test to my internal list of troubleshooting routines.

Post your responses in the comments section.

Michael Colombo

In addition to being an online editor for MAKE Magazine, Michael Colombo works in fabrication, electronics, sound design, music production and performance (Yes. All that.) In the past he has also been a childrens’ educator and entertainer, and holds a Masters degree from NYU’s Interactive Telecommunications Program.


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Comments

  1. Ryan Turner says:

    I’ve discovered that there are actually a ridiculous number of tricks people use.

    For example, a multimeter in VAC mode can detect very quick signals (serial and the like) that VDC won’t display..

    If your board has a short between Vcc and Ground (or any short really), poke around in ohm mode. Lower resistances mean you are closer to the bridge.

    If a single component on a board has blown and is shorting, hook it up to a power supply in CC mode and gradually increase the current until you can feel the bad part heat up.

  2. TWTechnical says:

    Hello fellow Makers,

    A few troubleshooting tips for both kits and broken items alike from an old timer (me)…

    After a thorough inventory of what works and what doesn’t work to pin down the actual problem, we’ve found that a substantial percentage of electronic problems can be detected visually. So give ‘er a good once over at the git go.
    You may look for: cold solder joints (esp. near anything that has a high thermal … ………… mass such as connectors, coils, transformers, etc), …………………………………………
    cracks in the circuit board, bulged or leaking capacitors, slight cracks or tiny burn
    marks in integrated circuits and transistors, discolored resistors, broken wires, . damaged connectors, unseated or not fully seated connectors, loose ground ……………hardware, blown fuses etc.
    Also, at this time you may want to operate all controls and buttons for a quick feel
    ( a simple stuck button won’t allow many devices too boot properly!).

    Next, if it’s safe to do so, give everything a good shake (or at least a enthusiastic tapping of components) to detect loose connections and/or cold solder joints.

    If you got yourself a dead kit ,you may double check your work against their supplied pictures or pictures you’ve picked off the ‘net.
    A quick ‘net check of your dead device’s model and malady may help as well but it’s easy to get distracted there!
    If you have a second identical and working device, well lucky you!
    We’ve found that after heating or beating an intermittent device, the best way to conquer an intermittent problem is through substitution (swap parts out into a working device or system and see if the problem follows the substituted part).

    If the above quick checks prove unfruitful, well you’ll just have to dig in deeper…so her’s s’more hints…
    Git yerself a voltmeter and make sure that all of the big electrolytic capacitors have around 60 -90% of what the rated working voltage WVdc on them. If they don’t , then you need to find out why. (It may be normal in some cases, but not often).
    A big resistor should be warm or (ouch!) hot. If it’s cold, you’ll have to find out why.
    (It may be normal in some cases, but not often).
    Remember the blown fuses you were looking for? just because they all look good doesn’t mean that they are good! Use an ohm meter to ensure that they are definitely good.
    While we are on blown fuses, put in another one. If it blows again you likely have yourself a short circuit. Time to check for shorted semiconductors… use a multimeter in the diode check setting to do so.
    We like using a metered variac (for ac) and an adjustable regulated power supply (for dc) to find shorted components. We simply power the shorted device by it and run up the voltage until the whole shooting match consumes about 90% of the fuses rating and the shorted components and anything in their path usually heats up enough to let their presence be known.
    It’s getting late …so if people are into it, I’ll continue this later… nitey nite!

    PS, That reminds me ….when you get stumped, it usually means you are clogged full of data, Go take yerself a long break, (or better yet shut eye) and let yer trusty ‘ol subconscious do its magic.

    1. Wow! These are some great tips! I like the last one especially, and I’d like to add to it. Looking at something with fresh eyes an often diagnose the problem, but finding another set of eyes can be fruitful as well – even if that person has less expertise in electronics than you do. Sometimes getting tunnel vision through the troubleshooting process can make you blind to the obvious.

      1. TWTechnical says:

        Thanks Michael… I like your suggestion!
        It kinda reminds me of hearing that companies like to hire new engineers fresh out of school before they develop bad habits and new preconceptions.

    2. James Bryant says:

      Don’t settle for one voltmeter – DT830 and similar digital voltmeters may be had on eBay for $5 (postpaid) from China and being able to measure voltage and current simultaneously is frequently very helpful. I have four on my workbench, two with probes, two with crocodile clips (although is is often useful to have a croc clip on the ground wire and a probe on the other).

  3. James Bryant says:

    If you designed and built the system yourself, particularly if it contains analog (including audio) circuits, prpoer grounding is very important. This article discusses some of the common causes of trouble:- http://www.analog.com/static/imported-files/rarely_asked_questions/moreInfo_raq_groundingClean.html

  4. Bill Meara says:

    Build your projects one stage at a time, and test each stage before moving on to the next.
    As long as you are working on low voltage gear, don’t forget to use your nose and your fingertips as troubleshooting tools — they can help you find problems by detecting parts that are getting too hot, or are starting to let out their “magic smoke.” Be patient. Take a break if it starts to drive you nuts. Consider troubleshooting to be like the work of a detective. Realize that troubleshooting is the best part of a good repair, and that a good repair is a very sweet thing. Get an oscilloscope! More words of wisdom (and tales of woe!) here:
    http://soldersmoke.blogspot.com/search/label/troubleshooting

  5. Dave Walker says:

    Interestingly enough, I was compiling a list of troubleshooting tips for a friend recently, who was renovating some faulty laptop PCBs. I came up with the following advice:

    • Get hold of circuit diagrams if you can. There’s really very little you can do without them, unless it’s something really obviously wrong with the system. Well done on those laptop schematics! As for what those obvious things might be…
    • First, visually check the PCB. A decent magnifier and light source is invaluable here. Those cheap little illuminated USB microscopes are brilliant, if you don’t have a big optical magnifier. Are there any scorch marks? Popped capacitors? Missing components? (!) Components out of place/skewed from their normal orientation? Cracked components? Physical signs of damage? Discoloured components or tracks? Obvious shorts across adjacent pins? (Little bits of wire or solder can easily form bridges, and are common causes of faults) Obvious dry joints? (If the solder looks dull, or cracked, or if the component leg moves when you poke it with a pair of tweezers, this can be an indication of a dry solder joint) Signs that a component has been removed, or replaced, or hand-altered in any way. You can sometimes see remnants of flux, a slightly brown sticky substance, around hand-soldering. Most machine-soldered PCBs are cleaned after manufacture, so you wouldn’t expect to see flux unless the PCB has been re-worked (this isn’t universally true, but is a handy rule of thumb.) Look for damaged components around any re-work, as the intense heat of the soldering iron can sometimes affect nearby components.
    • Correct anything you see, first. For dry joints, try re-flowing the solder joint with a little bit of fresh solder. To remove a component, always flow a little bit of fresh lead solder into the joint – this helps lower the melting temperature by the addition of lead, and makes it flow more easily, through the addition of fresh flux. For big components, try using a soldering iron in each hand, to get the heat required into the pads. Be careful not to fling a scalding hot component or lump of molten solder into your eyes! I’d recommend eye protection/a pair of glasses at least. Always “tin” the end of the iron with solder and wipe it clean on a damp solder sponge before starting any work. I’d really recommend getting a solder sponge, actually. They usually come with the stands, if you were thinking of getting a stand.
    • Sometimes, a PCB will be “conformal-coated”, which is like a clear varnish over the whole board, or parts of it, to keep moisture and other contaminants away from the components. This can make test/repair very tricky. Also, it really smells/stings your eyes if you heat it up with a soldering iron. Probably toxic & best avoided, unless you have no choice.
    • If the system does nothing at all, start at the power supply and work inwards. Check for volts on the supply, both before and after you connect it to your faulty system. If the volts drop significantly when it’s plugged in, you likely have a short on your system.
    • Track the power supply through the circuits, and check the voltage at every point. See how far the power gets before it stops. This is the easiest way to find faulty (or missing) components in the power network. Check input and output voltages of every regulator on the board.
    • Learn how to trace circuit diagrams across multiple pages. If you have a searchable PDF, use the search function liberally on net names to make sure you’ve followed every branch. There are often clues on schematics, where the designer’s written something helpful in a comment. Be sure to read any notes you find this way. Net names can also be a clue as to their function, if the designer’s been kind. You sometimes also find clues on the silk-screen of the PCB – little aide-memoirs for the designer that might nudge you into a discovery.
    • Fuses should be short-circuits in both directions – check none have blown. Continuity/resistance checks won’t usually work while the board is powered, because the voltages confuse the meter. Make sure it’s switched off before you try it. Working MOSFETs will conduct electricity in one direction, and not the other, due to the parasitic diode. If they’re switched on (activated), they’ll conduct in both directions.
    • Sometimes, a slightly faulty board will display a fault by getting very hot. You may smell it first! If this happens, disconnect the power and *Carefully* run your fingers over all the ICs & resistors to see where the heat is coming from. As a rule of thumb (no pun intended), anything over about 60C will hurt if you linger too long. Any component getting this hot without a big heat-sink is likely faulty. You may find that the hot component also looks discoloured on the metal parts. This is a dead giveaway that something’s gone wrong, and can often point you in the right direction for solving a fault.
    • Technically, all modern circuit boards are static-sensitive. Try to Earth yourself before touching anything, if you can. This is sometimes easier said than done… Something electrical with a metal case is usually a good bet, like a table lamp or something. Failing that, cold water pipes are a classic Earth connection. Just don’t drag your feet on the carpet on the way back from the kitchen ;o) Don’t wear synthetic jumpers, trousers, shirts or socks if you’re working on circuits, and try to avoid it on very dry days (such as when there’s a frost, or snow) if you can, as static buildup is more likely to occur then.
    • That said, it’s very rare to damage something with static – in all my years of working with electronics with barely a thought towards static discharge, I may have damaged 2 or 3 components altogether. Still, if it’s an expensive piece of kit you’re working on, it’s as well to take precautions, and static discharge can stress a component without obviously breaking it, but making it more likely to fail later on.
    • At some stage, a meter may not be enough for fault-finding. If you have a good understanding of the circuit, an oscilloscope is very helpful in diagnosing faults. Something like the PC-based Picoscope series is ideal for hobbyist use, as it’s a lot cheaper than a “real” one, and has more features than most hobbyist “real” scopes. It’ll also take up much less room! I plan to get one when I can afford it. However, it’s not a magic bullet. Looking at waveforms only helps if you know what you’re looking for, and that can take experience. You also need a half-working PCB before you can even begin to look at electrical signals.
    • Two very useful formulae are Ohm’s Law, and the Power calculation. V=IR (Volts = Current x Resistance), and P=IV (Power = Current x Voltage). V in Volts, I in Amps, R in Ohms, P in Watts. By transforming those two equations, you’ll be able to understand 75% of what’s going on in a system. For instance, if you know the resistance of a component, and the voltage across it, you can work out the current through the component and the power that it’s dissipating. This comes in handy for finding out when a piece of circuitry is drawing more power than you’d expect, and getting too hot.

  6. Question your assumptions. Or better yet, throw them away.
    I can’t tell you how many times I’ve been trying to track down a problem on a system I built, and I wind up limiting myself because I suspect something I did went wrong. Often enough, the problem is unrelated to what I did.
    Be methodical. Check and eliminate the simple stuff first.

  7. jamesbx says:

    1) Put a scope probe on your ground. You might be surprised what you see.
    2) If you tap components to look for a cold solder joint, be careful where you tap. I tapped a backlight inverter and a sharp wire end poked into my finger through the high voltage warning mylar and knocked me back in my chair.

    1. James Bryant says:

      A scope probe on ground can be very misleading. It will show you the potential difference (which will probably be varying at frequencies from Hz to MHz) between the “ground” where you apply the probe and the “ground” of the scope itself. The signal YOU see is not necessarily the signal that the circuitry on the “ground” where you apply the probe sees. As I suggested above, read http://www.analog.com/static/imported-files/rarely_asked_questions/moreInfo_raq_groundingClean.html