Points in Focus Photography

Control TL PocketWizards and Canon 580EX II Flashes

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I’ve received at least one email, and now a comment about sudden flash death induced by or related to LPA design’s Control TL PocketWizards. Moreover, a recent post on Canon rumors has a link to a paper, purportedly produced by LPA Design employees summarizing their investigation into flashes failing.

LPA design claims to have received reports from 120-140 customers that their 580EX II flashes, has been damaged within the past 18 months with similar symptoms. The symptom specifically is the inability for the damaged flash to produce controlled bursts. Lacking the ability to control the output, the flash will make a full power discharge all the time, even for TTL pre-flashes.

TLDR, The Brass Tacks

  • The potential exists with at least Canon’s 580Ex II and possibly Nissin’s Di866 (I’ve received a report of a Nissin Di866 being fried in a similar manner) flashes that a failure can occur.
  • The failure doesn’t appear to be related to heat buildup, so AC-5 soft shields aren’t a problem.
  • The failure appears to be strongly related to an electrical arc formed between the flash tube and the flash’s reflector, eventually frying the controller.
  • Replacing the fired controller, doesn’t fix the problem, and the flash will die again, even if it’s never used with a PocketWizard.
  • LPA Design claims that failures have happened to less than 0.5% of the MiniTT1/FlexTT5 units, and less than 1% of 580EXII flashes connected.

From my interpretation of the LPA design report, the problem lies in the flash and not the PocketWizards.

Moreover, it seems that if your flash exhibits defects that lead to the failure use becomes a consideration. In LPA Design’s tests, the arcing occurred randomly, even in HSS discharges where you would expect to see it in every “pop”.

Finally, it’s entirely likely that as many 580EX II flashes are failing on users who aren’t using PocketWizards at all, but we’re not hearing about it since they either aren’t being used as much or simply are being considered a case of random broken equipment by the users.

A Deeper Analysis

The LPA investigation tracked down the problem to 2 main areas. First, the failure is ultimately noticed when the insulated-gate bipolar transistor (IGBT) that controls the actual flow of current to the flash tube dies. Secondly, it appears that the IGBT dies due to repeated arcing between the flash tube and the reflector behind it.

Before I go any further, I want to take a moment to talk about how this stuff all works. The IGBT is used like a switch. It allows the flash’s onboard microprocessor, which run at considerably lower voltages, to accurately and quickly start and stop the flash’s discharge as needed without being fried. The IGBT is designed for this kind of work.

The big picture view is something like this. The camera or Control TL PocketWizard, talks to the flash using a defined set of signals, this is the ETTL protocol. These signals could say things like “set power to 1/2” or “Fire.” The exact meaning of these signals is defined by the protocol, and this is what everyone has to reverse engineer to produce Canon or Nikon compatible flashes.

The diagram below shows a simple example of how this plays out in a flash during a full TTL pre-flash and exposure cycle. The diagram shows time progressing from top to bottom. The first set of arrows (from left to right) represent the TTL commands sent to the flash by the camera. The step wave form under IGBT drive voltage, shows the control voltage applied to the IGBT by the microprocessor (this maxes out usually between 2.5 and 4 volts, and switching several 100 volts). Finally, the curvy lines on the far right, show the flash light output intensity (towards the right) and time (top to bottom).

The camera sends a series of commands to the flash’s microprocessor, as a digital (1s and 0s) signal. These settings tell the flash’s microprocessor what the desired power is and when appropriate instructing the flash to fire. The flash’s microprocessor converts these commands from power levels into how long it should leave let the flash fire.

When instructed to fire, the microprocessor’s changes the voltage on one of its low voltage signal lines, which in turn causes the IGBT to allow current to pass to the flash tube. When the desired amount of flash power has been emitted the microprocessor stops providing a signal to the IGBT which in turn stops allowing current to flow though the flash tube.

It is important to understand that in the scheme of things, neither the camera nor the PocketWizard has any direct control over the IGBT. The camera or PocketWizard can only tell the flash’s microprocessor what settings it needs, and when to trigger the flash.

In short, this means that it’s possible that these failures would have occurred even if PocketWizard’s never entered the equation.

Further, from my reading of the report, it appears to me that the problem with the failed/fired IGBTs is at least partially directly related to the flash tubes arcing to the reflector, which they shouldn’t be doing. This uncontrolled electrical arc can seriously alter the current levels the IGBT has to deal with or even propagate directly to the IGBT in a way it isn’t designed to deal with.

An electrical arc is like a miniature lightning bolt. Further, its ability to form is directly related to potential (voltage) between the surfaces that is forms between and how well that gap resists the formation (distance and conductivity). For example, an arc may from between two bare wires separated by air (as in a Jacob’s ladder) but insulate the wires and the arc will no longer form.

This brings me back to how a flash works, specifically that the voltage though the flash tube remains fixed and the timing is adjusted. In short, the PocketWizards can’t influence the voltage between the flash tube and the reflector, only the timing between when it turns on and off.

Moreover, it appears the gap between the flash tube and reflector is only at the threshold of spark formation, as, according to the report, it wasn’t seen in every test pulse, even if the power and discharge profile was kept the same. However, variations in alignment between the flash tube and reflector will change these characteristics and are specific to each flash made. Moreover, some flash designs, like the 430Ex II, have a much larger gap between the tube and reflector which makes it very difficult for the spark to form. This last part explains why some models of flashes are less susceptible to this failure than others.

The randomness of the spark means, the more the flash is fired the more likely it is for one that’s one that’s primed for failure to fail. This means, that using high-speed sync—one of the best reasons I’ve found for using the Control TL PocketWizard—raises the chances of failure due to the repeated firing of the flash over a single exposure resulting in more chances for arcing and thus frying the IGBT.

What this means for us as PocketWizard users

The real question to me is how do we, as PocketWizard users, move forward with this information.

My answer the first question, and while I can only speak for myself, is that I’m going to continue to use my Control TL PocketWizards. The potential failure seems to be directly related to the flash head (manufacturing and design tolerances) and not the PocketWizards.

I’ve had my two 580EX IIs in moderate use on my Control TL ‘Wizard’s for more than a year, and even longer using high-speed sync on camera. My feeling is if they were going to fail, they probably already would have; not that it would stop them from failing in the future. Further, since the PocketWizard’s high-speed sync mode isn’t driving the flashes any harder than a Canon EOS 40D would, and that’s what I used for most of their life, I’m not putting any more stress on them now, than I was before the PocketWizards.

That said; let me be clear about one thing, I don’t like the prospect of killing my rather expensive flashes. I’ve read LPA Design’s report, and while they’re the manufacture of PocketWizards, if you ask me, it’s in their best interest to fix any problems that exist or risk hurting the sales of their product. Moreover, their report is incurably detailed and technical to a point where I have a hard time believing they’re just trying to cover their own rears.

One thing to consider, if you are a Canon 580EX II user, who’s had their flash fail and is sending it off for repair, make sure the flash tube and reflector are inspected for damage and replaced if that is the case.

The LPA Design report can be downloaded from here and I’ve mirrored a copy here.

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