Canon 600EX -RTs Firing Every Other Shot?

Hi, guys! I had a wedding Sat. during which the on camera falsh would not fire for every other shot. I know it wasn't low batteries. What would be the first thing you'd check as the culprit?

What power setting were you at? How much time between each shot? Without knowing either of these, my primary guess is the flashes hadn't recycled completely.

Michelle Brooks Photography wrote in post #18148419
Hi, guys! I had a wedding Sat. during which the on camera flash would not fire for every other shot.

To establish clearly defined starting points:

1. Was the non-fire precisely every other shot? (i.e. shots 1,3,5,7,9 flash; shots 2,4,6,8 NO flash)
   
2. Can you reproduce the behaviour now using the same settings as 'on the day'.
   
3. How frequently were you shooting? Every 5 seconds? Every 2 seconds? As fast as you could?
   
4. What ISO / aperture / subject distance were you working at?
   
5. How do you know that it wasn't low batteries? This is THE most frequent reason and the great majority always absolutely swear it's not low batteries.
   

I think I was about 1/8 power, very little time between shots, maybe 2 seconds?

I will try re-producing. Yes, it was precisely every other shot. I had charged all batteries the night before, also, after the first incidence of non-firing during the processional, I changed the batteries anyhow before the second incidence. So I truly doubt batteries was the issue. More likely me not allowing enough recycle time. I'll have to check my setting for your 4th questions but I believe for the processional it was f3.5 ISO 640 1/200. Distance to ubject vaired, of course, as the members of the wedding approached.

Michelle Brooks Photography wrote in post #18148939
I will try re-producing. Yes, it was precisely every other shot. I had charged all batteries the night before, also, after the first incidence of non-firing during the processional, I changed the batteries anyhow before the second incidence. So I truly doubt batteries was the issue. More likely me not allowing enough recycle time. I'll have to check my setting for your 4th questions but I believe for the processional it was f3.5 ISO 640 1/200. Distance to ubject vaired, of course, as the members of the wedding approached.

Do you have the Audible Beep enabled. This will beep when flashes have recycled. Like a Metronome, you can follow the tempo.

does this occur with a different flash on that same camera?? It could possibly be a loose shoe on your camera.

Your flash can be getting tired too. Canon repair would look at it and say it's fine even though it is not. I've gone through the same issues with my three 580exii's i've killed. So far my 600ex-rt's have been surviving with perfect performance.

Sounds like there is something going on inside the flash. Wise to have a spare if not 2 spares during a shoot.

No, I don't, I don't want anything to call attention to me during weddings but wish I could!

At 1/8 it should recycle quickly.

I was having the same problems on Saturday but mine were shooting at or close to Full power.
Should have brought my damned battery packs.