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Unable to idenitfy a Diode :(

Discussion in 'Troubleshooting and Repair' started by daveylc, Sep 11, 2012.

  1. daveylc

    daveylc

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    Sep 11, 2012
    I know its rude to sign up and start asking questions but I'm really stuck.

    I've got a circuit that has failed (its camera flash), I've tested the components on the board and a particular diode is now showing any continuity and fails to give any result when i use the diode test on my multi-meter.

    However I'm unable to identify what the specs of the diode could possibly be?

    I've taken a photo (see attachment).

    Any help would be much appreciated.

    Thanks.
     

    Attached Files:

  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    Not rude at all. (Rude is signing up and spamming us)

    And this is a good question :)

    The problem is, it may not be a diode. Unless there's obvious physical damage, a diode almost always fails short circuit. Also, the markings are not typical of what I'd expect to see.

    Is it possible to get a photo of the whole board, and another of the reverse side of it? We may be able to reverse engineer part of the circuit and the context we then have will likely be informative.
     
  3. daveylc

    daveylc

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    Sep 11, 2012
    Thanks for the reply steve.. I'll take a shot of the bottom :)
     
  4. daveylc

    daveylc

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    Sep 11, 2012
    Here is the bottom of the board :)
     

    Attached Files:

  5. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    And the top of the board. Try to get it as focussed as possible.

    The good news is that it's not that complex :)
     
  6. daveylc

    daveylc

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    Sep 11, 2012
    Sorry it took me so long :)
     

    Attached Files:

  7. davenn

    davenn Moderator

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    Sep 5, 2009
    looks like I can see a diode symbol under it
    can you confirm ? :)

    Dave
     
  8. daveylc

    daveylc

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    Sep 11, 2012
    Yep, it definitely looks like a diode symbol, albeit they are all missing the line at the top of the triangle :)
     
  9. CocaCola

    CocaCola

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    Apr 7, 2012
  10. daveylc

    daveylc

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    Sep 11, 2012
    Thanks for that :) I'll order some from china land and hopefully it will be the fault :D
     
  11. CocaCola

    CocaCola

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    Apr 7, 2012
    Well my fingers are crossed, it's just a guess at this point... Although I would likely take the risk and test one out just for the heck of it as well...

    One thing to note is the huge forward voltage drop of those high voltage diodes, I'm guessing a lot of multimeters even on the diode setting push that level of voltage so they will always fail a test... Might be fun to take 4 or 5 9V batteries in series and test the diode that way...
     
    Last edited: Sep 14, 2012
  12. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    Well, there is one thing which indicates they're high voltage diodes, and that is the fact that the board has room for two diodes in series and this board has a single diode placed there (although it is not the one in question)

    However, I've been inside a few flash units before, and one thing they typically *don't* have are "special diodes".

    In addition, unless there is physical damage, I'd expect them to fail short circuit.

    In (yet more) addition, I'm not seeing all of the components I would expect to on a controller for a (very simple) flash, so this is only a part of the electronics I expect.

    So this is just the inverter, taking the low battery voltage and creating a high voltage to charge the main capacitor (which I assume the thicker leads connect to?).

    Perhaps the diodes (at least one of them) are to protect the circuit from spikes generated when the flash is triggered. If so, that doesn't explain all of them.

    Perhaps this is a very old flash, made when diodes were not easily available in high voltage ratings?

    The part number of the device in the plastic TO220 package would be good to know. (As would confirmation that the thin leads connect to the battery and the thick ones to the main capacitor. Oh, and the markings on the main cap -- Voltage especially.
     
  13. daveylc

    daveylc

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    Sep 11, 2012
    Camera flash was the easiest way of explaining its purpose, its a bit more complicated than that but thats roughly what the circuit is :D
     
  14. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    Perhaps you can do us the courtesy of telling us what it is then.

    As you can see, I made assumptions based on what you told me.
     
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