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New Contributor
Posts: 3
Registered: ‎02-10-2021

Canon 600EX II-RT drops link- HELP!

[ Edited ]

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!




Reputable Contributor
Posts: 751
Registered: ‎02-23-2020

Re: Canon 600EX II-RT drops link- HELP!

Sounds like you've already done quite a bit of troubleshooting.   I've never experienced this myself with the ST-E3-RT or any of the 600s (I have the original version 1 units).


Have you tried resetting the 600's to their default settings?


What mode are you using?


EOS 5D IV, EF 50mm f/1.2L, EF 135mm f/2L, 600EX-RT (x6), ST-E3-RT
EOS C70, RF 24-70 f/2.8L IS
Posts: 11,987
Registered: ‎08-13-2015

Re: Canon 600EX II-RT drops link- HELP!

What came4a body are you using?  Are you saying that you can maintain communication with a master, which I assume is mounted on your flash shoe.....but the communication to the slaves keeps dropping?


It sounds like you are in a very busy area, with lots of RFI.  If you move to a less densely populated location, does it still drop?


"Doctor told me to get out and walk, so I bought a Canon."
New Contributor
Posts: 3
Registered: ‎02-10-2021

Re: Canon 600EX II-RT drops link- HELP!

I have a Canon Mark III but this happens on or off the camera. The master always works but whichever is set to slave it drops link. I’m not in a densely populated area and this happens any where I go.
New Contributor
Posts: 3
Registered: ‎02-10-2021

Re: Canon 600EX II-RT drops link- HELP!

I have reset them all multiple times, same issue.
Frequent Contributor
Posts: 67
Registered: ‎11-24-2012

Re: Canon 600EX II-RT drops link- HELP!

In general I've found the radio really reliable. The link does go down when the transmitter goes to sleep but for me always comes back on when the camera wakes and wakes the transmitter. 


There was a factory / service centre installed firmware update forthe Mk1 600EX-RT and also the ST-E3-RT that was mostly to do with stability of the radio link. They said it was more beneficial when using multiple lights, often more than 5. You can tell if your transmitter was updated by opening the battery door. Next to the hinge and above the right hand AA battery there should be a white paint dot on updated transmitters. There's also a serial number range to check.


I wrote this post on my website in the past, and had all my 600EX-RT and the ST-E3-RT updated at Canon UK's service centre for no cost. 


Canon specialist trainer, author and photographer -
New Contributor
Posts: 1
Registered: ‎08-09-2021

Re: Canon 600EX II-RT drops link- HELP!

Did you find a solution to this? I have tried different cameras, channels, and four flash combinations. 


I haven't pulled them out in a few years, and am using the same settings I so reliably used before, based on saved memory configurations.

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