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  • EEVblog #366 – USB PSU Troubleshooting

    Posted on October 8th, 2012 EEVblog 7 comments


    Some troubleshooting on the USB PSU DC-DC Converter

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    7 responses to “EEVblog #366 – USB PSU Troubleshooting” RSS icon

    • The trick to reflowing those little leadless packages is to jab them a few times from the top with tweezers. That forces the solder around and makes it stick where it needs to be, and when you release it the capillary action realigns the chip to the footprint. If the chip doesn’t realign itself it probably a bad joint.
      I actually prefer them now because it saves stuffing around with solder wick for the next 5 mins cleaning it up.

      • Herman Toothrot

        Hi,
        i was just watching that video and didn’t get why you would expect a voltage difference across the Inductor with no load.
        As i understand it, the DC Voltage across an Inductor should be Current times Resistance, where with no load at all the Current should be quite low and therefore no Voltage difference. In my experience when checking the dc voltages on these types of DC/DC Converters you will hardly ever find a difference in DC Voltage Reading on the input and the output side of the coils with a good multimeter. If there is a difference then it’s most likely due to the multimeter not being able to filter the RF correctly.
        So i suspect that the powersupply might have been operational before the second reflow of the control ic.

        Greetings

    • Low voltage resitance, impedance checks around the circuit may have more quickly pointed to the cause.

    • I like the platypus on the pcb. :)

    • I work primarily in software, and just play with hardware, but I’ve been bitten many times by the same sort of troubleshooting issues when debugging software. It can be frustratingly difficult to troubleshoot your own work. When you first measured the wrong resistance, you attempted to explain it away by thinking there were other things in parallel, rather than probing deeper to recognize the problem. I’ve made similar rationalizations many times when confronted with evidence of a problem. You concentrated on the chip itself, where you expected to see the problem, rather than the other components, which you assumed were good.

      Often it helps to have another set of eyes look at a problem. I can’t count the number of times I’ve helped colleagues by merely standing over their shoulder and letting them explain their problem to me, and watching them come to the solution themselves during their attempt to explain. Sometimes I help by asking the right question (did you think of checking … ?), but other times I help by merely listening, without necessarily coming to understand their problem at all.

    • You should get a pair of these to probe those fine pith foot print even if you can get to the pin a pad is accessible most of the times except for BGA (I hate them).

      http://www.amazon.com/Fluke-TP88-Rigid-Probe-Length/dp/B000VRFL10

      Greeting from Bolivia

    • Heh, I noticed that C26 error instantly first time you tried to probe between that and the other resistor. :)

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