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    EEVblog #821 – Mailbag

    EEVblog #821 – Mailbag

    More Mailbag! Extended Teardown Video HERE Forum HERE SPOILERS: Military Mystery Item Teardown – UPDATE: ...

    • http://grapsus.net Grapsus

      It recalls me an incident with a small lamp I had. To turn it on, you have to touch the metal base. One day, the light bulb died when I powered it up, and 3 seconds later, the thing litterally caught fire, with black smoke comming out of it.

      Beside the fact that the touch sensor wire was 2mm away from mains, it turned out that in lieu of a fuse, they soldered a low value resistor in there. The silkscreen was saying “F1” but the component was a resistor. So when something in that circuit shorted, that resistor overheated and started burning!

      It’s very shocking that in civilized countries, some standards are enforced (everything regarding food) and some others (pretty much everything about electrical appliances) aren’t at all.

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    • Ingo

      there’s another spelling-error: at the beginning, on the right device, they separated “infor mation” – on the left device, they forgot ” mation”. (maybe new version – new Errors)…all the hard work on the casing and “interieur” and they fail on simple spelling ???
      Very interesting Blog – it’s awesome.

    • Worf

      Another fake one off the same blog – good to see how terrible it can get. And I think this one is slightly less terrible.


      Dave, you should rip apart the transformers just to see how a badly built transformer can be…

    • Scott Smith

      After seeing this video, I decided to tear down some (less pretentious) knock-off USB chargers. They don’t claim to be Apple products and even make the casing orange, but it’s the same form-factor. I bought them for small projects that needed a 5V supply from AC mains without much effort. I think I’ll reconsider now.

      My imgur album of photos:

      The product’s Deal Extreme page:

      – There is one attempt at slotting the board! ONE!
      – Also note the tape on the USB connector. Classy!
      – That blue disc is a 1nF 2kV ceramic capacitor where a safety capacitor ought to be.
      – The two TO-92 packages are S8050 and 13001 NPN transistors.
      – I lifted a pad while trying to articulate one of the capacitors for reading the manufacturer.
      – The caps are crap.

    • SD

      Do you have access to a hipot tester? It would be fun to see where it arcs over and at what voltage.

      If I remember it right, according to ISO 60950, a 240 V input requires 3 kV insulation between mains and SELV (safe low voltage, user accessible). I am guessing it wouldn’t even make 2 kV due to the 1 kV rated capacitor.

    • http://www.siliconchip.com.au Nicholas Vinen

      Unbelievable. I wouldn’t plug either one into mains – ever.

      I think it would be fun to design one of these properly. Some components can’t help but be large – basically, the two mains caps and the transformer, the switching transistor (well, largeish) plus any common mode filters, the optocoupler(s) (for separation) and so on. The rest can be miniscule so once you’ve gotten the big stuff in, there should be enough room left for a proper switchmode controller and so on.

      • Worf

        Look at the real teardown link – proper controller, proper safety isolation with huge creepage and clearances, isolation between high and low voltages, protection devices, etc.

        It certainly took a lot of 3D design to get it to fit together

    • paul

      Also watch Mike’s video’s of
      “Crappy psu analysis”, which is an even worse single transitor design.

      and “inside a reasnonable quality chinese psu” http://www.youtube.com/watch?v=1F3XlFI1JBo&feature=plcp

    • JG

      Great video – you can learn a lot by look at examples of how not to do something. On one of the PCBs Dave points out the silkscreen around the mains voltage traces. Does this silkscreen add any benefit by introducing insulation and therefore reducing the creepage seperation required? Any benefit if placing silkscreen over a trace? If there is a benefit, is this benefit recognized by any of the safety standard organizations? Thanks

      • http://www.eevblog.com EEVblog

        Certainly not recognised by any standard. I have not seen any data that says it makes any difference at all.

        • Fernando

          I saw the silkscreen between two power traces in many designs, specially between the pads of some connectors with little sepparation between its pins. I think it has something to do with optical inspection to avoid shortcuts between them.

    • http://www.thescreengeeks.com Matt Davis

      We used to carry some of these at our cell phone repair shop but they kept coming back as returns. To this day I still have a giant box of them in various colors.

      They will charge an already powered phone, but even sitting overnight, they will NOT charge a completely dead phone. Cheap stuff.

    • http://engineerllc.org Vernon

      HAHA! Steaming Piles 😛 Thanks for the fun Video Dave.

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    • Chupo_cro

      Hahahah :-) Awesome :-)

      Here’s another one:


      Brand new $0.99 5V 1A :-) USB charger I’ve bought as a few mA 5V power supply. Believe it or not – there weren’t any short circuits although it looked as quite a few pads were soldered together. However, it was just a matter of time before everything blew up :-)) so I removed the extra ‘soldering’ and cleaned up the whole PCB.

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    • Amanda Smith

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      it identify your device intelligently and meet its
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      this multi port charger could charge almost any USB device like
      Android and Apple phones.

      For details: http://www.amazon.com/CHOETECH-Desktop-Charger-Adapter-Technology/dp/B00MBDGVPM/

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