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Thread: ...Flash Gun - FYI.....

  1. #1
    Join Date
    May 2002
    Melbourne, Australia

    Default ...Flash Gun - FYI.....


    Just imparting knowledge....

    The flash light tube is NOT any the same as those
    light bulb that you have in your torchlight.

    Its a gas in alittle teeny weeny tube. Well
    in must cases these tube will have no Gas leak
    issues thus not the cause of the flash failing.

    The flash circuitry is not that complex after all.
    It has the basic 4 blocks.

    1- The charging circuit (with a transformer which
    less often will fail in any chance- Beware HIGH voltage)

    2- The Storage Circuit( Just a large capacitor-Norm rated @320V or more)
    Less likey to fail too.

    3- The triggering circuit (Just a tweeny weeny capacitor
    and the switch that you press or sync cord activated or
    light activated when in slave). This circuit trigger the
    ionisation of gas in the flash tube making it form a
    close circuit and thus discharge the Large Capacitor which
    gives you the BRILLIANT FLASH Pooff!!!!

    4- The Flash gas tube.

    From my previous experiences, most cases, the failure is due to part 3.
    For simple flash, its the Capacitor. A 20 cents capacitor. For slave
    units this will be parallel switch to the "Test button" and this capacitor
    Thus here is the symptoms when failure of PART 3 occurs.......

    This is how you see:
    - ON the flash
    - If no signs of charging, change battery......CORNY!!!
    - Listen to the Charging "whining sound" (for older circuit)
    - Check if the light (charged light) is ON.
    - If ON, it denotes that charging is okay. Part 1 works fine.
    - If did not turn ON, then either the charge sense light blow
    or charging circuit fail (PART2).- Verify by TEST flash if flash
    can FIRE, then the charing lamp need to be replaced.
    - Now , If charging is ON, then pressing the TEST BUTTON.
    - If Flash cannot fire(The charge LAMP remains ON),
    then the PART 3 circuit has problem.
    - IF Flsh Cannot fire BUT Lamp GOes OFF, thn the Flash tube (Part 4)
    needs to be replaced....

    SO as a rule of thumb....follow the above steps to verify
    before sending for repair. Else the shop guy will start to
    blame the Flash Tube....and start charging high price.....

    Know what you send in for.........


  2. #2
    Senior Member
    Join Date
    Jan 2002


    On Auto and TTL flash there is also a squelch circuit, the main purpose is to cut off the flash when the correct exposure is achieved.

    In auto mode there is a sensor built into the flash that measures the reflected light from the scene and cuts off the flash when it has determined that the correct exposure has been reached.

    In TTL mode, the sensor is built into the camera (mostly SLR, my guess). Film based TTL has a sensor measuring the light striking the film surface. When the correct exposure has been reached, the camera sends a signal through the hotshoe to cut of the flash. Thus the name Through-the-lens (TTL) flash metering.
    As complexity rises, precise statements lose meaning and meaningful statements lose precision.

  3. #3
    Senior Member
    Join Date
    Jan 2002
    Singapore, Singapore, Singapor


    How the electronic flash works

    an extract of a typical flash circuit from



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