Xenon Strobe repair

Discussion in 'General Electronics Chat' started by animateme, Jan 24, 2013.

  1. animateme

    Thread Starter New Member

    May 27, 2011
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    0
    Hello,
    I have an old xenon strobe (disco light) that had been stored for a very long time and when I tried to turn it on recently, it no longer worked. I first assumed it was the xenon tube bulb so I replaced it but it still does not work.

    I opened it up (circuit was inside wood box) to try and measure voltage at different points to see if I could determine any current interruptions but as soon as I plugged it in, there was a point on the back of the circuit that lighted up (burning) and even some smoke came out. I immediately unplugged it.

    Searching information on this I found this topic: http://www.aaroncake.net/Circuits/strobe2.asp , and it seems like my circuit is very similar. The burning came from one of the terminals on what seems to be the 4KV Trigger Transformer (see red arrow on attached photos).

    I am no electronics expert (I do own and can operate a multimeter), and that is where I would greatly appreciate any support on this forum, is there a way that I can troubleshoot this circuit to get it working again? Any suggestions or ideas?

    Thanks on advance for any comments.

    [​IMG]
    http://www.freeimagehosting.net/3t4m3

    [​IMG]
    http://www.freeimagehosting.net/krfks
     
  2. BillB3857

    Senior Member

    Feb 28, 2009
    2,400
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    It looks like the circuit board had some surface contamination that permitted arc over between the two conductors. Scrape out all of the black, coat with clear finger nail polish. Check for continuity on the trigger transformer since it looks as though the positive output of the voltage doubler arced to the secondary of the transformer. At one time, Radio Shack had the transformers.
     
  3. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    718
    You may want to check/replace the electrolytic capacitors, they are old enough that they may have dried out.

    When is the last time the strobe functioned? It looks like it was built in late 70s/early 80s.
     
  4. animateme

    Thread Starter New Member

    May 27, 2011
    10
    0
    --- Thank you for the response. It does seem like there was arcing as the burn is right between the 2 points. However, the strange thing is that this circuit had been working before without any problems so why would it suddenly burn like this at this point? ...would the fact that I plugged it in without the Xenon Tube Bulb in place have anything to do? That's the only difference in circumstances that I can think of that was present when this occurred. I had never tried plugging the circuit in without the Bulb. ---???
     
  5. animateme

    Thread Starter New Member

    May 27, 2011
    10
    0
    --- Thank you for the response. Is there a way that I can check the electrolytic capacitors? This circuit is actually from the 80s and the last time I used it must have been about 15 years ago. It worked fine the last time I used it until now that I took it out from storage. Thanks.
     
  6. BillB3857

    Senior Member

    Feb 28, 2009
    2,400
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    Running without the flash tube in place may have contributed to the flash over. With the tube in place, the flashing of the tube will tend to discharge the caps keeping the voltage lower than you would see without the tube. The suggestion to replace the caps is a good one based upon age but in order for the voltage to go high enough for flash over, they must be doing something in the doubler circuit.

    Was there any particular reason for testing without the flash tube?
     
  7. animateme

    Thread Starter New Member

    May 27, 2011
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    0
    --- There was no particular reason for testing without the flash tube. My intention was to test for continuity at each component and since the tube was not flashing I considered that there was no need to have it in place.

    How can I test the caps and if they are doing something in the doubler circuit to make the voltage go high enough?

    Thanks,
     
  8. #12

    Expert

    Nov 30, 2010
    16,298
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    Testing the capacitors would require applying the rated voltage to them and see if they leak current to ground. Fortunately, you have a voltage generator on hand...the flash controller board. Put it all back together and see if it ever develops enough voltage to fire the tube. Meanwhile, you can put a DC current meter in series with the capacitor and measuere the leakage current, preferrably you disconnect the capacitor from ground and measure at that end.

    I would also like to argue your statement that nothing changed in 15 years. Several things changed. The chemistry of the electrolytic capacitors has been eating the insides of the caps for 15 years, dust and humidity have been soaking into the circuit board for 15 years, etc. Leaving an electrolytic capacitor unused is about the second or third worse thing you can do to them. I recommend you wash the circuit board with detergent and water, then use a hair dryer to dehumidify the board. Then wait an hour and dry it some more. Cleanliness is very important in high voltage circuits.
     
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  9. sheldons

    Active Member

    Oct 26, 2011
    616
    101
    you can cut into the board and scrape away the conductive part of the pcb,desolder and resolder that pin on the tigger tx and as long as nothing else is at fault you should be up and running
     
  10. takao21203

    Distinguished Member

    Apr 28, 2012
    3,577
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    I have a Siemens 1000uF capacitor here from 1980. Still works.
     
  11. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    Many will still function. If you put them on an LCRZ meter or in a bridge, you'll see they no longer perform within the limits of the datasheet if the equipment has sat without power for a few years. If they are continually powered, that changes things, as the capacitors stay "formed'.

    At any rate, the essential characteristics of good capacitors made today far surpass a capacitor manufactured 30 years ago, ignoring the fact that that cap has sat idle an additional 15 years.
     
  12. animateme

    Thread Starter New Member

    May 27, 2011
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    Ok, thank you again for the advice. I will give it a try and report back.
    Thanks.
     
  13. #12

    Expert

    Nov 30, 2010
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    and I have (2) Sprague 14,000 uf @ 100V from 1975. I'll run them up to 100 volts right after I put on my bulletproof vest and full face plate motorcycle helmet.

    (Never mind below that, the work bench covers that part.)
     
  14. animateme

    Thread Starter New Member

    May 27, 2011
    10
    0
    Thanks for the advice but this is just a bit above my knowledge. I do have a multimeter but I am not sure if I want to mess trying to measure the powered circuit without being sure about what I am doing.
     
  15. animateme

    Thread Starter New Member

    May 27, 2011
    10
    0
    Ok, I scraped away the carbon area between the lines and put some nail polish on it as suggested. I placed the xenon tube back in and powered up. The arcing burn is no longer there! ...however, no strobe flash.

    So, I got rid of that issue (thanks again for the advice!), now I just need to get the circuit to flash that tube again.

    Assuming that the capacitors are dead from being stored and unused for such a long time:
    The current electrolytic caps on the circuit read: 22 uF, 250 WVDC

    As replacement for the electrolytic capacitors, I found these online from a local store:
    [​IMG]
    Electrolytic Capacitors
    The specs are:
    - Radial
    - Aluminum
    - 22 uF, 250 Volts
    - 13 x 29 mm.

    I assume that these will do the job, right? Or, is there anything else that I should consider when looking for the replacement?

    Would you suggest that I go ahead and replace this or is there anything that I could test before replacing parts?

    Thanks!
     
  16. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    The only problem I see is that your new caps are radial lead (both leads come out of the radius of one side), while what is currently installed are Axial lead (lead comes out on each end on the axis).

    If you can get them wired in without shorting, maybe use small diameter heat shrink, they could work, but it's better to replace with the same form factor component. Be sure to pay attention to polarity, Electrolytic caps have a tendency to explode if polarity is reversed.
     
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  17. animateme

    Thread Starter New Member

    May 27, 2011
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    Thanks thatoneguy. I did notice the difference between the axial and radial configurations. I did figure that I could get around this using a wire. I will be sure to pay attention to polarity. Thanks for the warning.
     
  18. #12

    Expert

    Nov 30, 2010
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    Sorry. I try to taylor my advice to fit the person asking, but sometimes I fail.

    Meanwhile, You are replacing the most likely suspects. If that doesn't work, I'm afraid you're going to have to learn about measuring live circuits.

    Let us know how it turns out.
     
  19. tubeguy

    Well-Known Member

    Nov 3, 2012
    1,157
    197
    Because of the flash-over its possible the trigger transfiormer or the SCR may be damaged also.
     
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