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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! 

View solution in original post

199 REPLIES 199

#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!

The number of IDs is irrelevant. They are almost certainly just numbers transmitted as part of the message to identify which master and slaves belong together in one set. I'm working on a device to connect existing 2.4GHz system which uses a 4 byte ID in the same way. The value 9999 would probably be transmitted as 270F hex and reducing the number of IDs would simply reduce the size of the message by 1 or 2 bytes. This would have no effect on performance or the reliability of the connection.

As you mentioned in a previous post Canon provides 15 channels whereas the 2.4GHz WiFi band doesn't allow this number of frequencies anywhere in the world. The system I mentioned above also provides 15 channels but these are closer together than the WiFi channels. This is not actually very relevant because the bandwidth of the channels is actually wider than their separation so they overlap anyway. Incidentally, the IDs of the system I'm working on are not number in order of their frequency but appear to be completely random - or at least I can't identify any logic to their order. I think we can assume that Canon has not used the same channel separations as for WiFi and the channel numbers are probably not comparable, if not even completely different.

I don't believe the number of IDs is, "irrelevant."  Strong RF interference can corrupt these values and large ranges have less tolerance.

This is why you must toggle radio to fix the issue.  Otherwise, I could just change the ID by one then back again and it'd re-link (or the channel).  It doesn't -- a drop is FUBAR.  And using ID 9999 -- the top of the range -- (and channel 15) has fixed my drops entirely (fingers crossed).

All of this is rather moot, as I provided before (emphasis is mine):

Part 15 of the FCC Rules...(2) this device must accept any interference received, including interference that may cause undesired operation.

You are of course free to believe what you wish 😉
The FCC rule you quoted simply describes good design practice for any interface. This is almost certainly what Canon fully intended, but it would appear that they have simply failed in some way. Yongnuo and Phoenix have managed to do a better job. It's very similar to a camera firmware issue except we cannot simply download and install a new firmware version (in contrast to the Yongnuo flashes!).

I hadn't planned on ego wrestling today...

Having completed yet another two hour test with my four 430EX III-RTs & ST-E3-RT (v1) -- all on channel 15 and ID 9999 -- without a SINGLE drop, I KNOW the following:

1) Canon RT IDs are HIGHLY relevant, 2) FCC rules are not "practices" but rules, and 3) Yongnuo (i.e. Canon RT) -- having owned them -- is garbage!

If anyone wants to bail on Canon, go Adorama/Flashpoint (aka Godox) and enjoy their customer service (I've read that Godox CS isn't so great).  Again, there is no Panacea.

P.S. Good luck on your device!