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Canon 600EX II-RT drops link- HELP!


Scenarios I have tried: 


Using Canon Transmitter ST-E3-RT as the master and (2) 600 EX II-RTs as slaves.

Using A 600EX as master and B 600EX as slave.

Using B 600EX as master and A 600EX as slave. 


I get the same result of the slave dropping link. The time varies. Sometimes it drops link in 4 mins, sometimes 10mins, sometimes 20 or more minutes. The only way to relink them is by turning everything off and back on.


All channels are the same. Yes, I have scanned for the best connection as well as every other channel and AUTO.

All IDs are the same. 


Not near a wifi-router or airport, I'm in a row home in Philadelphia. 


Using NiMh rechargeables and using freshly charged batteries for every test. Batteries are about 2 years old. 

I have spoken to 2 Canon service reps and neither of them has any idea what the problem is. I really don't have the money to spend on sending everything in for "repair". 


Any help is greatly appreciated, thanks!





Sadly I couldn't resolve the issue and Canon insisted they couldn't find a problem. I ended up buying new flashes - not an ideal outcome! 

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139 REPLIES 139

I tried channel 15 with no difference


Shame on you Canon for not addressing this. I have called into CPS on the issue and it’s treated like “wow we’ve never heard of this issue before”. Really disappointing for someone who just invested in 3 new EL1’s for 2022. Now I’m STUCK. 

I don't know if you ever watch Bob Davis -- who is a Canon Explorer of Light -- YT videos.  He rave(ed/s) about Canon's RT system (which is a big reason I gave up on 3rd party solutions and went pure Canon) but then readily admits to using RadioPoppers (which operate at ~902-928 Mhz) as a backup for when the RT system, "...isn't quite adequate."

When I first saw this -- searching around for a fix after experiencing drops -- it kinda pissed me off.


P.S. Canon -- whatever that means -- knows about it.


Canon needs to do two things:

1) redesign the transmitter/flash so if link is lost, the user from the transmitter can reset them remotely… or have a setting in the flash that re-seeks connection every minute, 5 minutes, 10 mi utes, etc based on user input. This way, as wifi standards update, it will extend this feature tpinntge flash.

2) offer past canon flash users either an upgrade price or a priority on new refurb models.  This will at least allow users some reason for brand loyaty. These flashes are 5x the Price of the knockoffs… don’t make me think going knockoff was the smarter way. 

#1 isn't possible.  If they could do that, then merely changing the channel or ID yourself would fix the issue.  But you can't.  I can purposely change the channel/ID on a slave, lose link, then change it to the correct setting(s) and it re-links.  I can walk too far away or introduce too many obstacles, lose link, and when I correct for that, it re-links.  But once the link DROPS, there's nothing I can do to get them to re-link -- no amount of channel/ID tinkering works.  I must turn radio off (on the slave) then back on.  It's as if a drop mini-bricks the flash.

I'd love to know the mechanism that's causing the drops.  Is it a frequency shift?  Like a machine designed to play only the black keys of a piano in a pitch black room, if it gets dumped...oops.  And neither the machine, nor the piano, "know" anything's wrong.

I believe Canon has too many IDs -- 10,000!  Other systems, which have IDs, have, at most, 100.  I doubt they're going to do anything firmware wise to fix this as the EX series must be sent to Canon for updates.  The EL series can be updated via the camera.  Maybe when the EL-5 comes out they will offer an update (ID reduction/greater freq spacing) just for the EL series.

I've been having great success with channel 15 and book ending my ID to 9999 or 0000.  This (guessing) limits frequency shift to just one direction.

And lastly, every trigger system in the 2.4 GHz band has issues.  Just spend a little time on a Godox forum!

I too found the most success with Ch 15 0000. 

Has anyone tried the RT noise flash sleeves they sell on B&H? People used to need them for the Pocket Wizard/580ex issue. Noticed someone suggested this on You Tube comments. Experimenting this week. I figured $12 was worth a shot for the time I’m wasting resetting these flashes WAY HIGH UP on light stands during an EVERY MOMENT COUNTS wedding. Before I lose even more money switching my whole lighting setup to Profoto. I am dumbfounded I have to say these things to Canon. 

I can find nothing about noise flash sleeve anywhere. Can you provide a link?


[Commercial link removed per forum guidelines and replaced with screenshot to facilitate discussion.]

Pocket Wizard make (or made) 2 versions. The AC5 is effectively a sock which covers the entire flash, including controls.
The AC7 is a hard shell that I haven't seen until today. It would appear to be open at the back but would appear to only allow the flash to be used in the "straight up position". This would probably ok for most purposes if using stands. However, the rigid shell of the AC7 might not be compatible with the form factor of the 600RT series flashes - this would need to be verified.

Bear in mind that they were intended to reduce interference from the flash unit. They are RF shields. Blocking RF leaving or entering the flash is likely to reduce the range or may even completely prevent the communication. If you want to try this idea I'd just start by trying it on just one flash first, before investing on a complete set.

Got my AC5 sock in today. Testing tomorrow!