Testing Flashtube?

Discussion in 'General Electronics Chat' started by hazim, Nov 25, 2010.

  1. hazim

    Thread Starter Active Member

    Jan 3, 2008
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    Hi all

    I'm repairing a "prolinca 250", it's a lighting device with flash used in photography. There was some problems that I've fixed, but still the flash /flashtube doesn't work. I don't know if these flashtubes have a fillamint inside them or there is a certain gas or what, looking to it I can't find a filament, maybe it's burned out completely... If it uses gas then how it burns?
    The tube has two terminals, i.e. it doesn't have filaments at each terminal like CFLs.
    Testing the tube for continuity gives open (infinity resistance). This maybe because the filament )between the two terminals is burned out or the flashtube uses gas.

    Here is a link about this same flashtube with it's picture:
    http://www.buy.com/prod/flashtube-5...ts/q/sellerid/10001650/loc/111/203462596.html

    So anybody knows how it works and how to test it?

    Regards,
    Hazim
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
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    At a guess, the flashtube is one that uses xenon gas inside for a bright white flash. The tube needs a voltage source on the terminals to supply power for the flash, and an additional high voltage discharge to ionize the gas into conductivity. There is useful information at the link - http://members.misty.com/don/donflash.html
     
    hazim likes this.
  3. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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  4. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    Also have great care.
    On the site Kermit2 showed is this published (partly shown):

    WARNING: This circuit is contains voltages and currents which can KILL if you are not careful. Charged capacitors will SURPRISE YOU! They can hold a lethal charge for hours! If you don't know much about working with high voltages or if you aren't crazy (like me) then DO NOT attempt to construct this circuit.

    So if you do not have the experience, do not even try it.

    Bertus
     
  5. hazim

    Thread Starter Active Member

    Jan 3, 2008
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    I don't want to build it. Circuits with flashtubes are of course dangerous since they use and store high voltage (sometimes may exceed 400VDC), also many of them stores the high voltage in large/high capacity capacitors which make them very dangerous.
    I work with electronics and repair TVs, cameras, microwave ovens... these also stores high voltage.

    I'm still trying to repair the"prolinca 250", but I didn't get it to work. To try it, there is an incandescent lamp that is burned out, it can be changed later, but trying the flash, the flashtube, is the problem as I said in the first post. How could I test or know if the "xenon" flashtube is all right or bad?

    Regards,
    Hazim
     
  6. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    About the only way to test a Xenon flash tube is in a working circuit. That's why others were suggesting circuits that you might build to test the tube. Then, it could be the high voltage circuit or the trigger circuit at fault. Do you have ~400VDC between the terminals on the ends of the tube when it is supposedly ready to flash?

    Ken
     
  7. hazim

    Thread Starter Active Member

    Jan 3, 2008
    419
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    I should have done that before.. I tested the voltage on the flash tube now, the voltage is about 540VDC!
    There are two huge capacitors each is charged to about 270VDC (in series they give the 540V)

    This voltage doesn't go or decrease since the load (flash tube) is not lighting to consume the stored power and discharge the capacitors.

    Regards,
    Hazim

    Edit: The voltage across the tube reached 580VDC now.
     
  8. hazim

    Thread Starter Active Member

    Jan 3, 2008
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    It seems you escaped when you read about 580VDC? :D
     
  9. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    The next step would be to check for the 4KV+ high voltage trigger output. But, without a high-voltage probe and an oscilloscope, I'm not sure how you could do it. There may be some suggestions buried here: http://www.repairfaq.org/sam/strbfaq.htm

    Ken
     
  10. hazim

    Thread Starter Active Member

    Jan 3, 2008
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    Is it like CRT flyback transformer testing? I've read that it can be tested using a test screwdriver placed about 1cm far from the HV line terminal or so...?
     
  11. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    I don't think so. It's just a single, high voltage, almost-no-current pulse.

    Makes me wonder ...If you shuffled across a synthetic carpet, building up several KV of static electricity, then touched the trigger wire (fine wire wrapped around the tube), would a good tube flash? Or, would the HV winding of the trigger transformer just bleed it off?

    Ken
     
    hazim likes this.
  12. hazim

    Thread Starter Active Member

    Jan 3, 2008
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    Actually I've tested all of the circuit board components except the triggering transformer. This still maybe the left problem, but I'm not sure if it's easy to test it (ohms testing) especially the two windings are not obvious since the transformer is made (or covered..) with epoxy material.. Tomorrow I'll right down here what happens with me and post some pictures.

    Regards,
    Hazim
     
  13. hazim

    Thread Starter Active Member

    Jan 3, 2008
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    [​IMG]

    This is not the circuit of the device I'm trying to repair, but it shows some similarity to it.

    The trigger transformer in my case is not connected as in the circuit exactly, specifically the connection between one primary winding terminal and one secondary terminal doesn't exist, but the connections with the thyristor for example are the same.
    The transformer has a very low primary winding resistance, near zero. The secondary winding resistance is about 140Ω.
    Assuming the voltage pulse is 10,000V then the primary winding voltage would be around 70V. This calculation is not 100% right, but it gives me idea about the primary winding voltage just to know if it's safe to test with my multimeter.

    Testing the voltage at the primary gave me about 100V (AC) which decreases few volts when I press the triggering switch. But when I placed and soldered the transformer in its place, there was no voltage again...

    The circled thing is the trigger transformer

    [​IMG]

    [​IMG]

    More pictures are attached...

    Regards,
    Hazim
     
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  14. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    100Vac across the primary doesn't sound right. I think there should be no voltage across the primary. What do you read, Vac and Vdc, across the SCR's anode and cathode? The capacitor between the SCR's anode and the primary should block any DC and the big flash capacitors should filter out any AC when charged.

    Ken
     
  15. hazim

    Thread Starter Active Member

    Jan 3, 2008
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    I was wrong... I tested the voltage on the primary today, there is no DC voltage, I didn't tried anything else, this device really tired me. But I'm 99% sure that there is no problem with the board and I misdoubt about the flashtube. Would the piezoelectric igniter of a lighter help in triggering and thus testing the flashtube?

    [​IMG]

    Regards,
    Hazim
     
  16. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    Now there's an idea. I think I would disconnect the trigger wire on the tube from the trigger transformer. You would need the connect one electrode on the igniter to the trigger wire on the tube. Connect the other electrode on the igniter to the ground end of the secondary of the trigger transformer. Separate the wires enough so you dont get an arc between them.

    Ken
     
  17. hazim

    Thread Starter Active Member

    Jan 3, 2008
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    I thought about trying that idea, I'll try it and write here what happens. If it the tube didn't flash then....??? it may be bad and it may be OK.... we can't be sure except if it flashes when trying this idea... But I'll try and see.

    Regards,
    Hazim
     
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