Whelen xenon strobe inop

Discussion in 'General Electronics Chat' started by wrenchbender, Jan 23, 2010.

  1. wrenchbender

    Thread Starter New Member

    Jan 8, 2010
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    This is an older 12 volt strobe and power pack that I'd like to fix. When connected to a 12 volt pwr source, I can hear the electrolytics winding up.
    For some reason, the pwr isn't being discharged into the xenon. I'm not totally sure how it works, but maybe you have some suggestions, things I could check out on it. the electrolytics are 300 volt and both do fully charge. A strange small bulb inside seems to slowly iluminate, die, then repeat funtion.
    Which part of the circuit releases the charge into the xenon? is it worth messing with?
    thanks.
     
    Last edited: Jan 23, 2010
  2. hgmjr

    Moderator

    Jan 28, 2005
    9,030
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    Can you post a photo of the device so that we can get a look at it?

    hgmjr
     
  3. VoodooMojo

    Active Member

    Nov 28, 2009
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  4. VoodooMojo

    Active Member

    Nov 28, 2009
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    a little oscillator circuit pulses through a step-up transformer, stores charge in the capacitor, then releases charge through xenon strobe (quick explanation)
    the little bulb indicates the charge is complete and the circuit should be outputting to the xenon but it obviously isnt

    here is all the info you will ever need on the subject:
    http://repairfaq.cis.upenn.edu/sam/strbfil.htm

    be EXTREMELY careful with this stuff!

    attached is a TYPICAL circuit

    looking at this, we can see the SCR, the output coil, or the xenon can be defective.
    maybe not the SCR as the neon is indicating that the cap is charging and something is discharging the cap so....

    we will need a schematic of your unit and some voltage readings
    what is the Whelen model #

    be CAREFUL!
     
    Last edited: Jan 23, 2010
  5. wrenchbender

    Thread Starter New Member

    Jan 8, 2010
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    I've added a couple of photos of the device for your viewing pleasure. Just below the larger tranformer is a much smaller one about 1/2 inch wide. Its covered up by the aluminum base. thanks again for the info.
     
  6. VoodooMojo

    Active Member

    Nov 28, 2009
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  7. wrenchbender

    Thread Starter New Member

    Jan 8, 2010
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    Unfortunately no, Its an old aircraft strobe. I tried googling the model number but didn't find any schematics. Here is the model: HR, DF-14
     
  8. BMorse

    Senior Member

    Sep 26, 2009
    2,675
    234

    The HR/DF/14 is a Self contained Double Flash Strobe that runs on 14 volts...

    the new Whelen replacement is >> Model HRCFA P/N 01-0770029 just in case you need to purchase a new one....
     
  9. VoodooMojo

    Active Member

    Nov 28, 2009
    503
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    you probably won't find a schematic. it's an aviation thing and field repairs of electronics is typically a no-no. Assistance is non-existent if you are not FAA certified.

    we need to isolate which components are good or bad.

    the neon is lighting so we are assuming the caps are working.

    we will need to check the SCR gate to see if it is getting triggered.
    we might assume that it is because the neon is pulsing. but verify.

    if the gate is being triggered we need to verify voltage at the anode and ground at the cathode of the SCR.

    Check the input and output of the fire transformer. Follow leads back from Xenon for this.

    Check the output to the Xenon.

    Be VERY VERY careful!!
    we love you and don't want to see you get hurt!


    there will be 400 volts all over this thing and as much as 4KV at the output end.
     
  10. bertus

    Administrator

    Apr 5, 2008
    15,638
    2,343
    Hello,

    The high voltage present can be lethal:

    Xenon Strobe Safety

    There are two potential hazards in dealing with the innards of electronic flash and other xenon strobe equipment:

    1. The energy storage capacitor. Even on small pocket camera electronic flash units, these are rated at 100 to 400 uF at 330 VDC. This is 5 to 20 W-s which is enough to kill you under the right (wrong?) conditions. Hot shoe or side mounted electronic flash units have energy storage capacitors which are usually larger - typically 300-1000 uF or more. High performance studio speed lights may have 10 times this capacity and at much higher voltages resulting in even greater energy storage. Xenon strobes for pumping of solid state laser rods and other industrial and scientific applications may use many kV power supplies with 1000s of W-s energy storage capacitors - touch one of these and you will be but a puff of vapor in the wind... High voltage with high energy storage is an instantly deadly combination. Treat all of these capacitors - even those in tiny pocket cameras with respect. Always confirm that they are discharged before even thinking about touching anything. On larger systems especially, install a shorting jumper after discharging just to be sure - capacitors have been known to recover a portion of their original charge without additional power input. Better to kill the power supply than yourself if you forget to remove it when powering up.
    2. Line connected (no power transformer) have all the dangers associated with AC line power in addition to the large power supply and energy storage capacitors. Always use an isolation transformer when probing line connected systems. However, keep in mind that the power supply filter capacitors and energy storage capacitors remain just as deadly.
    This is a part from this page:
    http://repairfaq.cis.upenn.edu/sam/strbfaq.htm

    Greetings,
    Bertus
     
  11. Wendy

    Moderator

    Mar 24, 2008
    20,764
    2,534
    The little wire wrapped around the tube is a 4KV injection point. It ionizes the gas in the tube so the main charge, 130-350VDC, stored in one of the large capacitors dumps it's charge all at once. Once the charge is gone the gas become inert and nonconducting again.

    You should see see the main charge (the 130-350VDC I mentioned) on the input pins of the tube. If it is there its the 4KV pulse circuit that is malfunctioning.
     
  12. wrenchbender

    Thread Starter New Member

    Jan 8, 2010
    8
    0
    Thanks for all the warnings. I'll be very careful with the unit. I don't plan to reinstall it on an aircraft after its repaired. Its just a well built unit that I'd rather repair than throw away and learn something in the process. Once again, I appreciate all the info.
    What a wealth of knowledge there is here.
    Thanks.
     
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