Page 2 of 3 FirstFirst 123 LastLast
Results 11 to 20 of 29

Thread: Fixing a Novatron

  1. #11
    8x10, 5x7, 4x5, et al Leigh's Avatar
    Join Date
    Dec 2010
    Location
    Maryland, USA
    Posts
    5,454

    Re: Fixing a Novatron

    Quote Originally Posted by E. von Hoegh View Post
    One way to be certain would be to solder a jumper across the capacitor while you are working on the unit.
    E.,

    That's the stupidest idea I've ever heard.

    Shut up before you kill somebody.

    You have no clue what you're talking about!

    - Leigh
    If you believe you can, or you believe you can't... you're right.

  2. #12

    Join Date
    Feb 2006
    Posts
    3,142

    Re: Fixing a Novatron

    Quote Originally Posted by Leigh View Post
    E.,

    I suggest you shut up before you kill somebody. You have no clue what you're talking about!

    - Leigh
    Did you read the rest of my post? Where I said to discharge the thing first? At least this would allow the OP to replace other parts without danger.

    And kindly tell me why this is a stupid idea.
    One man's Mede is another man's Persian.

  3. #13

    Join Date
    Sep 1998
    Location
    Loganville , GA
    Posts
    14,409

    Re: Fixing a Novatron

    Add my two cents. A friend was the factory service technician at Norman many years ago and he had a bad scar on a finger where he accidently discharged a cap in a head while servicing it. The damage went in one side of his finger and came out the opposite side. Scars on both sides. Not pretty and it was his job to repair them.

    When I sold Rollei Studio Flash Systems; 250ws, 1250ws and 5000ws units I was demoing a Rollei E5000 unit (5000ws, required 220V 3 phase AC) at Armstrong Industries in Lancaster, PA. On the third shot the unit blew up because what they thought was a 220V line was actually 440V. Unit flew across the studio and crushed itself against the far wall. There is tremendous power stored in fully charged caps. Not a DIY project. Even if you think you are trained.

  4. #14

    Join Date
    Aug 2010
    Location
    New Orleans, LA
    Posts
    585

    Re: Fixing a Novatron

    Exactly! There are very specific procedures for discharging high energy caps and "sticking a wire across the terminals" is likely to result in an explosion in your face. At the very least, a resistor (or some unknown value) needs to be included in the discharge circuit and there's most definitely the potential for a hysteresis charge building back up in the cap after it's been discharged if this isn't done correctly, or the wrong value resistor is used in the discharge circuit.

    Add that to the fact there are probably many caps in a Novatron pack arranged in an array, so it's more than just a simple matter of "jumping out a cap" to make it safe. And most dangerous of all, at some point, the repairer will need to power everything up again, which presents yet another risk of deadly electric shock or explosion if something hasn't been done correctly, or some value has been changed - say, installing an unknown inductor in a head, or something like that.

    Bottom line - too risky to fool with and for the $60 a good used head is likely to cost, it's not worth it!

  5. #15
    8x10, 5x7, 4x5, et al Leigh's Avatar
    Join Date
    Dec 2010
    Location
    Maryland, USA
    Posts
    5,454

    Re: Fixing a Novatron

    Quote Originally Posted by E. von Hoegh View Post
    Did you read the rest of my post? Where I said to discharge the thing first? At least this would allow the OP to replace other parts without danger. And kindly tell me why this is a stupid idea.
    I'll repeat my previous post.

    YOU DON'T KNOW WHAT YOU'RE TALKING ABOUT.

    - Leigh
    If you believe you can, or you believe you can't... you're right.

  6. #16

    Join Date
    Feb 2006
    Posts
    3,142

    Re: Fixing a Novatron

    Quote Originally Posted by E. von Hoegh View Post
    Fools rush in, where wise men fear to tread....

    One way to be certain would be to solder a jumper across the capacitor while you are working on the unit. Be sure to discharge the cap. first. The jumper is important because hysteresis of the electrolyte can allow the cap. the build up a charge all by itself, after you've discharged it.
    That said, listen to everyone else and don't mess with it unless you know exactly what you are doing.
    There, for those who cannot be bothered to read.
    One man's Mede is another man's Persian.

  7. #17

    Join Date
    Aug 2010
    Location
    New Orleans, LA
    Posts
    585

    Re: Fixing a Novatron

    My last point - which everyone knows already anyway - these studio strobe packs are designed to release VERY large amounts of energy in MICROSECONDS! Think about that!

  8. #18
    Moderator
    Join Date
    Apr 2009
    Location
    Northern Virginia
    Posts
    5,614

    Re: Fixing a Novatron

    Quote Originally Posted by Leigh View Post
    E.,

    That's the stupidest idea I've ever heard.

    Shut up before you kill somebody.

    You have no clue what you're talking about!

    - Leigh
    It's not that dumb, but I agree it is potentially dangerous advice, because the precondition to installing that jumper (full discharge) is not at all trivial, no matter how much E.v.H. boldfaces it.

    Large amateur radio amplifiers that use vacuum tubes that are biased by high-voltage power supplies that have huge filter capacitors use two strategies to discharge and then ensure that the caps and tubes stay discharged: They use a large ballast resistor, of sufficiently high resistance not to undermine the voltage being supplied during use, to bleed off residual charge. And then they have a mechanical shorting bar that collapses onto the high-voltage bus when the case is opened. The voltage in question for those amplifiers is usually in the 2000-3000V range for equipment radio amateurs use.

    Not all of them have the shorting bars, but they all have the bleeder resistors.

    Sometimes those resistors are opened, and sometimes the diode strings used to rectify the power supply output are opened. In those cases, the charge may not be bled off. The shorting bars are deep inside the case and short long before one's hands can get near it, but a significant discharge using the shorting bar is still a memorable event that can cause further ruination. The power head for a studio flash system is just not much different at all from the power supply used for a radio amplifier. My Speedotron power head has bleeder resistors, and after a minute or two the capacitors require a complete recharge when the head is next turned on. But portable flashes usually hold the charge to minimize battery consumption and don't have bleeder resistors.

    The standard tool for ensuring that the charge is bled off is to use a "chicken-stick", which is a probe with a high-dielectric insulator about a foot long as a handle. It has a metal tip that is grounded by means of a jumper wire. It's a safety device intended to be used only after an orderly discharge of the capacitor, however, like the shorting bar. I measure the voltage at the danger points using a 6000-volt probe (which cost more that the Fluke meter it connects to), but if there is high voltage present, there's a real question about how to get rid of it.

    And therein lies the danger. Discharging a capacitor suddenly might have really spectacular results, including spraying bits of it all over the room. And the tool used to discharge it works because it provides a path to ground for those hundreds or thousands of volts, with the attendant risk that the person holding that device is in that path.

    The injury severity issue is related to how much of a person is in that path, and that's what will determine the damage it does. Bob's technician acquaintance demonstrates what one finger in the path means. Most apply the "one-hand" safety technique, to minimize the probability that the really important bits (heart, etc.) are in the path, but it's not easy to predict what that path will be or what part of the body found itself unintentionally attaching to the ground path. I was fiddling with a Rollei potato-masher flash some many decades ago, and got just a part of the jolt from the flash capacity as I was attempting to discharge it using a probe. I was heavier than the flash so it was the flash unit that took the horizontal trajectory to the far wall. But the muscles in that arm were sore for several days.

    The danger, then, is that 1.) it isn't easy or obvious to discharge a capacitor of that size, and 2.) if one does not know or have a way of measuring the charge state, there is considerable risk resulting from placing that shorting jumper across the capacitor leads before soldering it. And the consequences of a mistake are potentially severe.

    The correct way is using a hi-pot probe with a discharging bleeder resistor to measure the drop in voltage until it reaches something safe to handle (under 40-50 volts with dry fingers).

    Rick "properly afraid of high-voltage work" Denney

  9. #19
    8x10, 5x7, 4x5, et al Leigh's Avatar
    Join Date
    Dec 2010
    Location
    Maryland, USA
    Posts
    5,454

    Re: Fixing a Novatron

    Discharging a capacitor improperly can KILL you.

    IT WILL EXPLODE.

    E. It's obvious you're more concerned with your own ego than with the safety of other members.
    You should be ashamed of yourself.

    - Leigh
    If you believe you can, or you believe you can't... you're right.

  10. #20

    Join Date
    Feb 2006
    Posts
    3,142

    Re: Fixing a Novatron

    Quote Originally Posted by Leigh View Post
    Discharging a capacitor improperly can KILL you.

    IT WILL EXPLODE.

    E. It's obvious you're more concerned with your own ego than with the safety of other members.
    You should be ashamed of yourself.

    - Leigh
    Fine. I'll never comment on anything potentially dangerous again, since too many are willing to read parts of a post and ignore other parts.
    I hadn't noticed anyone mention the fact that hysteresis in the dielectric/electrolyte can cause the capacitor to "recharge" itself and deliver a nasty shock - or much worse in the case of a studio flash. Temporarily shorting a high voltage/high capacity capacitor is the only way I feel safe around one, it's not unheard of for them to build a charge from static electricity while on the shelf.
    I had assumed that my final sentence was warning enough to anyone with the ability to read.

    Rick, thanks for pointing out the use of bleeders and chicken sticks.

    Once again, as I wrote in my first post: "That said, listen to everyone else and don't mess with it unless you know exactly what you are doing".
    One man's Mede is another man's Persian.

Similar Threads

  1. Jobo, LPL, Omega, Novatron, Technical support.
    By Greg Blank in forum Darkroom: Equipment
    Replies: 4
    Last Post: 5-Apr-2011, 04:42
  2. Fixing and toning
    By Fred Braakman in forum Darkroom: Film, Processing & Printing
    Replies: 9
    Last Post: 5-Jan-2007, 16:48
  3. fixing thermometer
    By poco in forum Darkroom: Equipment
    Replies: 11
    Last Post: 30-Aug-2006, 19:57

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •