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600 EX-RT not firing


I bought a set of Canon 600 EX-RT flashes. I am a wedding photographer so I use both of them often on 2 cameras. Unfortunately one of the flashes only fires ever 5-6 times as the other one works just fine. Anyone has similar problems? 

Thank you for any help. 


I am a little confused by your post. First you say you use both of them and them on 2 cameras. You say one of them works just fine but the other one only fires 5 or 6 times.

You never tell us what camera model or models you are using, what camera mode you are set in, what mode each flash is set in.

Are both flashes set the same? Did you try clearing the settings on the flash that isn't working the way you want and starting fresh with it?

You really need to supply a little more information so someone can help you properly.


I use 2 cameras Mark 3 and 5DR, each has a flash for evening shooting. Both flashes are set to ETTL. 

OK that helps. Which camera is the Flash on that is not working properly? You said you have a Mark 3. Is that a 5D Mark 3?

You said the you have a flash on them for evening shooting, but are the camera's in P mode, M mode, TV mode AV mode or what? I am not trying to be difficult but you are not being clear on your settings here.

Also your 600EX flashes can be set in ETTL and be set in A mode or M mode.

Did you try clearing all the settings on the flash that was giving you the issue to see if it would function properly once you reset it?

Also since you have one flash that is functioning properly did you try moving that one that was working properly to the other camera to make sure it worked properly on that one?

If you have one flash that works properly on both cameras then you will isolate the problem to the flash itself. Then its either the flash or the settings on that flash.



I have exactly the same problem - except | dont have 2 flashes.  Did 2 weddings this weekend and my 600 EXRT only fired about every 3rd or 4th image, I would get an on exposure image - then the next one would be very underexposed - the flash had fired but like at half power I would say, the next one maybe the flash would not fire at all.  I managed to get through the weekend but it was a nightmare for me.  I have reset the flash in as much as pressing the 2 buttons together to clear everything - it was set in etttl.  I changed batteries constantly thinking that may be the problem and I also tried a battery pack to see if that made a difference and it didnt.  I was shooting in either AV or Manual - settings averaged f1.4 and f2.8 as I was in a very dark hotel yesterday - iso averaged 1650 and shutter speed of 1/80.  I have a canon 5D3 and also a 6D - I used both cameras yesterday and had the issue on both cams - so looks like the issue is with the flash unit itself.