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Sparks at red multimeter tip

Discussion in 'Hardware' started by techkuestions, May 24, 2018.

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  1. techkuestions

    techkuestions Thread Starter

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    i’ve googled it and not found an answer, but whenever i hold the red multimeter probe against the dc jack’s output pins on the motherboard i get clear sparks, everytime, with multimeter set to 20 V. I’ve detected no difference in function or readings since the sparks occurred. What could be the cause of these consistent sparks at this one spot on the pcb/motherboard when pressing it with the red multimeter pin?
     
  2. cwwozniak

    cwwozniak Trusted Advisor Spam Fighter

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    It might help someone here to help you if you told us the brand and full model number of the motherboard and/or the brand and model number of the computer. Which jack and which pin your are touching with the red probe?

    What type of multi-meter are you using?

    Is the black probe's tip of the multi-meter connected to anything?

    Is there anything connected to the jack when you are probing it?

    Is the sparking happening right where the probe is touching the jack's pins?
     
  3. kenbok51

    kenbok51

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    First of all there should be no power OUTPUT from a motherboard except for perhaps to an external device like usb, monitor or mouse and audio. I suspect you mean power input. A photo posted about what and where your touching would be helpful. You don't have to actually do the touching just use a photo editor to draw circles around the point your describing. DC voltage is polarity specific which means positive touching positive and negative to negative. If you get them reversed you will get sparks and the meter will read incorrectly. The same is not true for AC which is not polarity specific.

    If you are testing a laptop which has an external power supply you can determine which pins are positive and negative by testing the supplies plug. As a matter of fact if you have an external supply there should be a legend on it somewhere and perhaps a legend on the laptop showing the plugs polarity. Something like this - C would mean the outside of the plug is negative and a dot inside the C shown as a + would mean the inside of the plug is positive. But just knowing that it would still be hard to tell which solder joint on the board goes to which point of the plug unless its really obvious.

    What type of voltage tester are you using? Is it digital with an LCD screen reading, or the old style type with a swinging needle? I actually prefer the old style myself.
     
  4. techkuestions

    techkuestions Thread Starter

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    Ok, so i’m using a digital multimeter, and it’s of model allosun em830. The sparks occur when the power supply is plugged into the laptop, and i place the red pin on the power supply’s tip by the dc jack, and then touch the output pins of the dc jack on the motherboard with the black tip.



    it’s a lenovo flex 4 where the dc jack is connected to the motherboard via a cable, as opposed to plugged straight into it.
     
  5. techkuestions

    techkuestions Thread Starter

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    Btw, i’ve tested the power supply, and indeed the positive is on the outside and the negative’s the inside. Power supply’s good, virtually new.
     
  6. cwwozniak

    cwwozniak Trusted Advisor Spam Fighter

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    That digital multimeter should have a high enough input impedance so that it shouldn't have any chance of sparking. Am I safe to assume that you have the red probe cord plugged into the Multimeter's V-Ohm-mA jack and not the 10 Amp jack?
     
  7. managed

    managed Trusted Advisor Spam Fighter

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    Also make sure the red and black probe tips are only touching one solder pad each, if either gets close enough to 2 pads with different voltages you will get sparks.
     
  8. techkuestions

    techkuestions Thread Starter

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    cwwozniac, yea the red’s into the V and the black into the com.

    managed, i think that may very well be the issue, because i did touch in between pins (couldn’t find a magnifying glass), now the only question would be if such sparks lead to guaranteed damage.. as i said i haven’t noticed any malfunction/s myself.

    Btw, being small pins i went over them from right to left til i saw a multimeter reading, and possibly moving it slightly further started the sparks..
     
  9. managed

    managed Trusted Advisor Spam Fighter

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    You have to be careful or the probe tip can make a short between + to - and if there's a small enough gap a spark will occur but even without sparks a short could cause damage.

    I think you got away with it though.

    It's a good idea to put the - black probe tip onto something metal like the outside of a Usb port which will be a good 'ground' connection then just use the + red probe to test voltages at other parts of the laptop.
     
  10. techkuestions

    techkuestions Thread Starter

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    Yea, seen others on youtube always grounding the black probe, wasn’t sure why, thought i read it’s supposed to go to negative, while the red goes to positive.

    Btw, a repair shop told me it’s the motherboard (frankly i figured it’s not the dc jack as it shows 20v), and (predictably) not exactly what on motherboard was wrong (i think most western repairshops mainly do full swaps 2 cover overhead, in most cases), but am curious as to what it could be. Have gone over the mb quite comprehensively with the multimeter and get readings (was looking for a short or dead spot, couldn’t find any).
    What mb component is likely to short during a power surge, or is that random?
     
  11. managed

    managed Trusted Advisor Spam Fighter

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    Ground and negative are the same thing on laptop motherboards.

    It's impossible for me to say where the problem is on the motherboard.

    You're correct that repairs to a motherboard aren't common, you need expensive equipment to remove any bad components even if you could find them. Usually you do have to replace the motherboard.

    What laptop make and model is it ?
     
  12. techkuestions

    techkuestions Thread Starter

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    Well it seems the multimeter won’t react if i put the black tip on a screw or usb port (set to voltage and laptop plugged), not sure what i’m doing wrong.


    The motherboard is intel, searched for circuit diagram online, couldn’t find any for it, guess it’s not that old.


    Btw, any clue as to why the multimeter, when testing continuity sometimes beeps even if displays only zeros, but sometimes doesn’t beep despite showing a positive value? Is it cause it’s a cheaper one? My understanding was that continuity testing either meant a beep or no beep, and that number readings were from dc or ac tests. Guess i’m still learning..
     
  13. managed

    managed Trusted Advisor Spam Fighter

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    Some meters will give a resistance reading on the continuity setting and if the resistance isn't low enough there is no beep. Never use the continuity or resistance settings on anything that has power.

    You still haven't told us the make and model of the laptop.
     
  14. kenbok51

    kenbok51

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    I solved the tiny solder points problem by making alligator clips (one red and one black) that slide onto the meters pins fairly firmly, and then using the alligator clips I clip onto them actual needles or dress making pins so that I have very accurate touching points. It's kind of hard to describe but the alligator clips have a tube at one end where you would connect wires to them to for making jumpers or whatever. By using needle nose pliers I pinch the tubes to the correct size to tightly slide over the meter tips. The clips I have also come with flexible color coded covers (red or black) so I don't get them, mixed up.
    It's also handy to have the black clip to attach to a negative point like mentioned above, something you know is a ground, and then your free to use the needled red clip to poke around more accurately. I've been doing this crap for a long time now and I have learned ways to get around these kind of issues. I keep pins and alligator clips attached to my meters case so I don't lose them.
     
  15. techkuestions

    techkuestions Thread Starter

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    Great. The laptop model is lenovo flex 4 version 1570. It has some type of intel board with i7, can find the model if necessary.

    I think i may have used the continuity with power on a cpl times, til i looked it up.


    Btw, tested the capacitors, and all of them get close to 20v readings, except to the one nearest the power button which only read about 0.12. Is that normal?
    Battery and dc jack inputs are good.


    As for microsoldering, saw kits not very expensive. Do wonder if some places could replace a micro component, such as capacitor, and how much it’d cost, as motherboards are fairy expensive.
     
    Last edited: May 28, 2018
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