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    #1

    Need explanation of video

    Can someone please explain the technique in the video below? Where is he connecting his test leads? Does anyone else use this technique? From what I got out of the video you'd heat up each component and see which one results in the highest ohm value. Which ever one is the highest is the culprit? Is this correct?

    http://www.youtube.com/watch?annotat...&v=9R8T7lPql18
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    #2
    Re: Need explanation of video

    The test leads are connected to ground and the 3.3V supply rail. Measuring 3.45 ohms on this bus indicates that almost 1 amp would be necessary to maintain the 3.3V, which is way more than expected for that little board. One of the 15 components connected to the 3.3V rail must be faulty.

    The assumption is that the failed component will have a steep positive temperature coefficient, meaning that its resistance will increase dramatically when it gets hot. So each component is heated individually, and the one that causes the biggest increase in resistance is considered to be suspect. When he hit the CPU, resistance went way up. He then lifted the 3.3V lead on the CPU and showed that the bus resistance went up to 5K, proving that it was indeed the CPU at fault.

    The technique sounds like a good one if the suspect is a failed semiconductor device. But it probably won't work well for mechanical type shorts (solder bridges, etc.)

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      #3
      Re: Need explanation of video

      What is not obvious with the technique is that the multimeter shown in the video is also a Fluke 189. The Fluke 189 is a 50,000 count multimeter and can measure ohms with 10mOhm (0.01 ohm) resolution in the 500 ohm range.

      Most multimeters only show 0.1 ohm resolution so it may not be obvious that the resistance is rising like on the 189.

      Anyway, I learned something new so thank you. Unfortunately, I don't have a need for a hot air rework station.

      The one board that I do have this is obviously shorted has a whole bunch of electrolytic caps and if I applied hot air even near them, I would probably kill their lifespan or altogether.
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