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  1. #1
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    locating short on pcb

    Assuming an unknown shorted path exists on a PCB which had be soldered with all components. How to find out where occurs the shorted path? Considering that excluding the path on board, there are internal paths in on board ICs which also possible induce the shorted path.
    I think it also can be a general methodology question. How to find the shorted path among multiple possible paths?
    Needs for your good idea.
    Thanks.

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    find short circuit pcb

    I think this would me more of an intiution analysis. 1st what makes u think there is a short. Once you have that reason clear in your ming, you can try isolating the sources. I think this is the best start. Then of course get busy with the soldering iron and the Multimeter !



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    locate short circuit pcb

    It is good to have the schematic diagram and the PCB layout .. This helps to identify which pads should not have a short circuit ..
    And the recipe is somethong like this:
    success (in finding short circuit) =patience+multimeter+magnifying glass



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    test equipment to find pcb track shorting

    If some components on board have JTAG, then it will significantly simplify this process. Especially, if you have some BGA packages.



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    how to find a short on a circuit board

    There are inexpensive pieces of test equipment that can be used to find shorts on circuit boards. They are microohm meter bridges that use an audible signal to help you trace out the short.

    One of the least expensive, and one that works really well, is described at:

    http://www.eds-inc.com/leak.html

    The cost is about $200 US - I've had mine for about 5 years, and it works like a champ!



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    find pcb shorts

    it is not necessary to buy short circuit checking devices connect one used battery(with low voltage) with an LED or a piezobuzzer and check the traces for any short



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    how to find a short on a pcb

    Quote Originally Posted by electron_boy
    it is not necessary to buy short circuit checking devices connect one used battery(with low voltage) with an LED or a piezobuzzer and check the traces for any short
    With such device you can figure out that all wires on board are shorted together, even if they are not!!! Try to connect such device between GND and VCC lines - it will show that they are shorted (if your device uses 5V, 100 mA - it will be exactly 50 Ohm, that are detected by such simple device as short!)

    That is the reason for high price of short detectors - they precisely measure in range less than 1 Ohm.



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    locating pcb short circuits

    One of the methods can be to use stabilized power supply with current limit. First set the current limit of the power supply to expected current consumption of your circuit or device, and corresponding supply voltage. Because of the short circuit, the current consumption of the circuit can be normal or exceede expected value. In the case the consumption is greater then expected voltage of the power supply will drop and in this way you will prevent eventually burned component. If the voltage of PS remains normal the next step is to find component that does not operate correctly. If voltage drops you may increase current limit and find which element has raised temperature. This is a bit risky but may bring success. Measure node voltage and try to find abnormalities.



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    pcb short circuit finding techniques

    My experience follow what others have said.

    But my usual rule of thumb is to troubleshoot this way.

    1. A Good visual inspection.
    - sometimes a strey wire strand or some other foreign object can cause short.
    2. If no obvious defects are noted then I would check most likely culprits.
    - first capacitor, then coils.
    -- components like resistors usually burn out and open, I have yet to discover a shorted resistor.
    -- open components are usually easy to spot. but this is about a short so.
    -- capacitors don't show signs of shorting out but usually do so I go after them first.
    -- finally i check coils. these do short-out. mostly I find they partially short out so the defect is not obvious. We had a similar problem, it took us a few days to discover the culprit was a coil. it didn't look burned out but it's impedance characteristics were significantly wrong.

    Hope this help to further discussion
    wa



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    Re: How to find out the shorted path on PCB?

    I had a pretty simple solution... but not sure will works for all cases...
    1st, u need to have a moderate accurate multimeter in ohmic sensing. my case i m using fluke-177.

    let say short occur in between Vcc and GND, u can check the ohmic of in between them, and problem now is to find the location, since VCC and GND is everywhere in ur circuit.

    a total short circuit will shows 0.1ohm in my multimeter, and the short circuit VCC shows value of 0.3ohm. means it is a little short in somewhere else. Then i fix my negative probe at GND at a specific location, n positive probe will try to probe the VCC at others location. u might found some places have a little bit lower ohmic value, like 0.2ohm... or maybe even higher value. when u found the smaller value, tat's will be ur location the traces short circuit.

    this help narrow down the debugging area, then rest of it u need to find the most possible short circuit location with ur intuition.

    Hope this can help... i just found out this is quite easy and useful...



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    Re: How to find out the shorted path on PCB?

    i have a continuity tester based on LM741. It buzz when resistance is below .25 ohms.
    Similar like,
    Connection Tester - Test Gears Circuits Schematics - Electronics Tutorials and Hobby Projects
    Electronic continuity tester circuit diagram using 741 op amp | Electronics Projects Circuits Diagrams and Schematics
    You don't have to spend 200$ for testing, even digital meter is sufficient for this testing as yesABC have stated.
    I know. I know. And once more - I don't know.
    I am too old and would not have enough knowledge to judge, and only have made some remarks in order not to be called ignorant.



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    Re: How to find out the shorted path on PCB?

    I check the easy things first. A 5 to 10 power magnifying glass is invaluable.

    Solder blobs where they ought not be. Also cracks in solder joints. Cracks in board traces. Especially where the board might bend due to cables being plugged in and out, etc.

    It's a natural step to want to try, to reduce supply voltage and see how current draw changes. However we have to think twice, because this can cause digital devices inside an IC to improperly go into partial conduction instead of normal on-off action, causing overmuch current flow, which could ruin them.

    What level of undervoltage is safe? Not sure.

    I test voltage levels at all pins of the IC. If they are all the same, I know there's a problem (such as innards fused together).

    I have to be careful when I use my analog ohmmeter on the lowest range setting (X1). It contains a 1.5V cell and it will send 60mA through circuitry. So I'm careful to start on a higher ohm range.

    After working on the problem I want to test it. But I don't want to blow a fuse. To limit current the first method I think of is to put a bulb in series. Awkward to set up, but it tells me a lot of things I need to know. A bright bulb tells me there's a short. A dim bulb tells me it may be fixed, and I can try supplying full power.



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    Re: How to find out the shorted path on PCB?

    There is a device called a digital current tracer which traces low impedance shorts in logic circuits. It only works on circuits where the current is changing levels though. It does not locate dc current shorts. But it is useful for logic circuits with multiple paths. It can be used in conjunction with a logic pulser to trace relative current paths.



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    Re: How to find out the shorted path on PCB?

    Back in the 90s, I worked at a place where they had an instrument for finding shorts on PCBs.
    It so happened only I was able to use that instrument (requires good hearing).
    It changes its sound's pitch as you get closer to the short.

    I was able within 5 minutes to pinpoint a short with tremendous accuracy on a PCB of any complexity.

    I think it was called "The Whistler". I forgot who made that.
    I've been looking for it ever since on the web, to no avail.

    If anyone knows where I could find one, I'd be so grateful.

    Short of making one myself...
    This was the best ever tool I came across; I wonder why those folks stopped making them.

    PS. Onetime I found something that I thought was that, bought it, and sent it back - it happened to be a simple squealer that squealed at the short. As useful as using a DMM on the "buzz" setting.



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