600ex-rt slave flashes randomly stop firing - please help!

[PhotoMouse]

I've scoured the interent trying to find a solution for the problem I'vve been having and I can't find any posts where people are having the exact problem I am. I'm hoping maybe someone on here has had this problem and might be able to propose a solution. Thanks in advance for any help!

I have 4 Speedlite 600EX-RTs I've been using for about the last 2 years with very few issues until recently. When shooting events I typically use two on cameras (5d Mark III's) and two as slave flashes for room lights. Everything will be working fine and then at some point I look down and realize my room flashes are not firing.  The on camera flash will work and the link light will still be green but the slave flashes won't fire until I power off the master flash, then they will start working again for a while until they randomly stop firing. Usually during something important like a speech or the hora.

Just for clarifcation, the ID #'s are all set the same, I keep them all on auto channel, I'm using newish eneloop batteries and I feel like the problem starts too early in the day for it to be battery related. 99% of the time I am on manual across the board and my power on the slave flashes is never more than 1/32 or so.

Any suggestions would be greatly appreciated!

[diverhank]

I haven't encountered this problem myself.  There are a couple of things I can think of:

1. Not sure why you choose to use Auto Channel.  I'd manually set the channel for your 4 flashes.  This eliminate one potential problem with communication.  A middle channel seems to be a safe bet. You can also check for an optimum channel ahead of time.

2. Cfn 10 specifies the time the slaves would auto shut off - either 10 minutes or 60 minutes. I'd choose 60 minutes. Cfn 11 allows either 1 hour or 8 hours as the time the slave units will wake up from auto power off when you press the Test button on the Master unit.  Once a slave goes asleep, you need to wake it up by pressing the Master Test button or risk failure on the first shot.

[PhotoMouse]

Thanks for the reply! I've already got both those custom functions set and it happens in the middle of shooting so I don't think the slave flashes are going to sleep.

I've been using auto channel bc according to the manual they are supposed to automatically choose the best channel when you use auto. I've always used the flashes in this manner and have never had any problems until recently which is a why I'm at such a loss.

Any other thoughts?

[RobertTheFat]

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@PhotoMouse wrote:
Thanks for the reply! I've already got both those custom functions set and it happens in the middle of shooting so I don't think the slave flashes are going to sleep.

I've been using auto channel bc according to the manual they are supposed to automatically choose the best channel when you use auto. I've always used the flashes in this manner and have never had any problems until recently which is a why I'm at such a loss.

Any other thoughts?

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I wonder whether the fact that there are more rf devices in play than are ever simultaneously used might confuse the external flashes about which channel is in use. Why not run some tests with the channel manually set, just to rule out the possibility.

[kvbarkley]

Could it be getting confused having two masters? Does it happen if the other camera is off?

[TCampbell]

You can ask the flash to 'scan' and provide a report of what it thinks is the best channel (it generates a graph showing how much chatter is on various channels).  I usually use this to try to find a relatively clear channel and set all the devices to use those.

One other thing...

You mentioned you have two on-camera flashs and two off-camera flashses... is it always the very same on-camera flash unit that you have to reboot to clear the problem?  e.g. if you swapped on-camera flashes with the other camera, does the probelm go away?

It's entirely possible that there is something flakey about that particular flash unit.

It's easier to fix when you have something that can reproduce the problem on-demand.   When it happens randonly (nothing you can find will make the problem occur) then those are more difficult to trouble-shoot... which is why I might suggest just trading flashes with your other camera to see if the problem follows the specific flash unit.

If the problem happens regardless of which flash is the 'master' then my guess would be it's environmental (radio frequency interference, etc.)  But if the problem follows just one specific flash then of course that would point to a flakey flash that should be serviced or replaced.

[georgezinser]

dont know if you figured it out but i have the issue as i found that it was the djs wireless dmx lighing as they are 2.4GHZ on the same band as the flashes. this is the 3 time i ran into this and i had to break out my pocket wizards and everything was fine with them as thy are on the 300MHZ band

[RobertTheFat]

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@georgezinser wrote:
dont know if you figured it out but i have the issue as i found that it was the djs wireless dmx lighing as they are 2.4GHZ on the same band as the flashes. this is the 3 time i ran into this and i had to break out my pocket wizards and everything was fine with them as thy are on the 300MHZ band

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Wouldn't using a different channel in the 2.4GHz band have had the same effect?

[georgezinser]

I tried this but the output power for the dmx lighing is more powerfull and you get inerferance. i also had this happen when a powerfull acess point system was at a hotel venue as the wifi is on 2.4GHZ. 2.4GHZ is very congested frequency in the US. im starting to run into inerferance more and more. when they do work thy work great.

[RobertTheFat]

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@georgezinser wrote:

I tried this but the output power for the dmx lighing is more powerfull and you get inerferance. i also had this happen when a powerfull acess point system was at a hotel venue as the wifi is on 2.4GHZ. 2.4GHZ is very congested frequency in the US. im starting to run into inerferance more and more. when they do work thy work great.

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My WiFi expertise is a bit dated. but it used to be the case that most consumer devices were set to default to one of two or three channels (I believe 6, 11, and possibly one other). Since most users wouldn't bother to change from the default, those channels would be very congested. So the trick was to choose a channel in the trough between two of the defaults, thereby minimizing interference. You might try that if you haven't already.