Learning to repair flash equipment.

Discussion in 'Lighting' started by waynecrider, Jun 2, 2005.

  1. waynecrider

    waynecrider Member

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    Although I don't have a background in electronics, I would like to learn to repair my broken flash equipment. What are my choices for schools and online opportunities that I might be able to make a 2nd career out of this?
     
  2. Donald Miller

    Donald Miller Member

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    I would assume that a course in electronics would enable you to diagnose and repair this equipment. I am guessing that you are speaking of studio strobes.

    The basics are that you will have a rectifier circuit to convert AC to DC current. Additionally you will have a bank of capacitors wired for proportional discharge based on the switching circuit. (The capacitors are present to store the DC) Additionally a trigger circuit to discharge the capacitors into the flash tubes.
     
  3. jim appleyard

    jim appleyard Member

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    Just a word of caution: I'm told that the capacitors in a flash unit have enough electricity stored in them to bounce you across the room. Please know what you're doing before you attempt to fix one.
     
  4. Ole

    Ole Moderator Staff Member Moderator

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    It's true - they do. All big high-voltage capacitors do, and the flash ones are among the worst. They can be very, very painful - if you're lucky.
     
  5. waynecrider

    waynecrider Member

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    I don't know what their discharge voltage is, but I have been unlucky enough to be shocked by a 50 mfd 440 volt a/c capacitor. Just one of the many benefits of being an a/c mechanic for 28 years.
     
  6. Canuck

    Canuck Member

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    The flash caps usually have a little more power. Ones I have worked on were on average about 2200 uF @ 600V in banks of 4. I assumed a power pack I working on, was discharged, but decided to make sure with a screwdriver (me assuming again it was just a small charge left). Scratch one screwdriver as it was spot welded to the cap after the bang :smile: Was a bit of a surprise.
     
  7. Donald Qualls

    Donald Qualls Member

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    For whatever it's worth, the charge stored in a *single* small consumer strobe's capacitor is considered to be in the potentially lethal range. Most such will store between 350 V and 450 V when ready to flash, and will still have 200 V or higher even weeks or months after the flash was last powered; they're capable of discharging at more than 1000 amps (until something in the circuit melts or the charge is dissipated). The vibrator/inverter that charges the capacitor has a peak output voltage of around 600 V, though it doesn't source much current -- but some parts of that circuit are high frequency AC (up to a few kilohertz, as I recall), which has its own hazards (deep tissue burns are no fun).

    Even the rechargeable batteries in some units are potentially hazardous -- a 4 cell nickel-cadmium battery pack, even with one bad cell (so unable to operate the flash) can dump enough current through a wedding ring to cost you the finger.

    It's very possible to repair flashes and do it safely, but you need to know stuff about high voltage, capacitor safety, and high current batteries that even most electronic technicians don't seem aware of. Be careful!
     
  8. waynecrider

    waynecrider Member

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    I like to tinker and am more interested in repairing my small strobe stuff, not the big battery packs, although I'm sure you can get hurt on the small stuff as well. I think that mostly it's bad bulbs that need to be replaced more then anything. I'm not afraid of electricity, you just have to know the procedure. Since no one really answered the question, I suppose it will be harder to learn then i would think.

    Donald, thanks for the quick low down. I can understand the way you put it.
     
  9. gordrob

    gordrob Subscriber

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    I was thinking of repairing a flash myself at one point. After I read the information in this site I decided that I would leave it to someone with the know how. This site has a a lot of information and links on how and what to do. Take time to read the disclaimer part way down the first page.

    http://repairfaq.ece.drexel.edu/sam/strbfaq.htm#strbdis

    Gord
     
  10. 127

    127 Member

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    I had a crack at a TINY flash (guide #15, run from AAA batteries - the baby ones).

    The circuit is simple enough - they're not exactly rocket science. Trouble is even this baby was enough to cause me to exercise my anglo-saxon dialect. Seriously painfull, if not dangerous.

    After about three hits (despite discharging, and removing the batteries), I wore rubber gloves, which solved the problem.

    Do not underestimate the kick these things can give out. Anything larger than the one I was playing with would do serious damage.

    Simple removing the power, and/or discharging is NOT sufficient to make them safe.

    Ian
     
  11. bobfowler

    bobfowler Subscriber

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    If it's a common flash (such as a Vivitar 283), you might be able to get a factory repair manual with circuit diagrams, test point voltages, and other helpful info.

    The main flash cap of a rather small (50 watt second) on-camera flash can pack a hell of a whallop!
     
  12. Roger Krueger

    Roger Krueger Member

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    I have a knuckle that still can predict the weather 5 years after a 450V 1100uf zap. I got hit index finger to thumb. The cap was about 100V over design voltage due to a charging circuit problem.

    283s are pretty simple to take apart and fix. The things most likely to fail are the bulb (easy fix) and chopper transistor (not hard, but the transistor used on earlier models is no longer available anywhere. If you really need one I've got a stash that probably exceeds my lifetime requirements). Zoom head flashes are mechanically a lot more difficult a get apart and back together properly.

    Modern TTL flashes are pretty unlikely to be easily repairable.

    There's almost certainly not enough money in fixing old flashes to make a career or even paying hobby.

    The safe way to discharge a cap is with insulated clip leads and high-wattage resistors. My regime is a 5W 47K for 5 minutes, 5W 4.7K for 5 minutes, 5W 470ohm for 5 minutes, then (old) screwdriver short.

    DO NOT just short a fully-charged cap. It will take a chunk out of the screwdriver, make a noise that's a good imitation of gunfire, and likely damage the capacitor too.

    One neat thing you can do to a 283 is hook up an external battery pack, yank out the battery compartment and put in a second capacitor "donated" by another flash for an easy doubling of your power output. Hard on tubes though.
     
  13. waynecrider

    waynecrider Member

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    Geez, it takes that much to totally discharge a unit?
     
  14. bobfowler

    bobfowler Subscriber

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    Excellent advice. Better safe than zapped.

    Yeah, but it's sooooo much fun to arc weld! :smile:

    Yup, that's what they did when they made Armatar units, except they put a Lumedyne flashtube in a box on top of the head. The spec sheet says it's a 300WS unit, and judging from the pop, it's pretty damn close! I love to use mine bare-bulb at wedding receptions - EVERYBODY gets "blue dot" syndrome! :smile: