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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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122 REPLIES 122



I have seven Canon 600EX-RT flashes. The options and radio control over the flash units is incredible. The capability and usability was second do none. I have only been able to use them in less than three minute sessions for three years. Imagine rotating around the room, reaching into soft boxes, turning the units on and off to resync.


I suspected WiFi interference. Yet, having turned my system off, I knew I could not manage my neighbor’s dozen visible hotspots. Time to find another solution…



Making a move from hot shoe based modifiers would also be expensive, and took months of research. I selected Westcott strobes, which are mid weight and semi portable, but most of my artificial lighting shots are done in the studio. Knowing this, I had yet to test the Canon flashes outside. 


I took the Canon flashes for a 2.5 hour ride to purchase the Wescott strobes. One disconnect occurred at hour 2. Could have been a low battery, but the entire array did not disconnect, as continually experienced in the studio. For my units, the issue was not batteries, but interference, which was unresolvable by performing any and all of the setting gymnastics and superstitious workarounds. Could channel settings work for you? Perhaps. Good luck.



Armed with an FJ-X3, two FJ400s strobes and two FJ200 strobes, I began testing options. Using the FJ-X3, I set it to “Canon” mode, and configured as per Wescott suggestions. This is a must. Although marked Canon, the devices communicate over a Wescott proprietary protocol. The initial test flash or camera flash is not always reliable (Wescott confirmed). Subsequent shooting was 95% reliable, and stayed connected for hours. The FJ-X3 takes care in connecting to the camera body. Given it’s compatible with multiple brands, the pins must line up correctly. Best to fully unscrew the lock ring, move the unit as far forward on the hotshoe, check again, hold in place, then tighten the lock ring.



To use Canon flash units in conjunction with Westcott, you set the FJ-X3 mode to “Canon RT”, which uses the Canon protocol. Any current generation Canon camera can use either. 1) FJ-X3 to Canon flashes worked, but was less reliable than the ST-E3 to Canon flashes. 2) FJ-X3 to Wescott strobes over Canon RT was MORE reliable than what I had experienced before with the ST-E3 to Canon strobes, but eventually broke down 3) ST-E3 to Westcott Strobes over Canon RT was MORE reliable than the FJ-X3 to Canon flashes. Interesting! 4) When using Canon RT mode, Wescott strobes were finicky, but became less reliable when adding a 600EX-RT.  Lesson learned: The Canon protocol is not reliable with interference. Unfortunately, the Westcott gear in “Canon” mode is not compatible with Canon flashes in any way, unless you enable the Canon flashes with third party triggers. You must use Canon RT to do this.


The XJ-X3 and strobe menus are fairly easy to use, but are not as well laid out as Canon, and can be finicky. For example, the menu allows you to set settings outside the range of capability for a camera/flash system, in particular, with Canon RT. You must also set an RT ID for the Wescott strobes to trigger. The strobe modeling light and settings will change over the Wescott protocol, giving you a sense it’s connected. Occasionally you need to “prime” the unit by changing settings, test firing, or turning the modeling lamp off and on twice.



Having worked in and around technical support for decades, I will say Wescott support is stellar. They made no excuse for their own failings, worked to resolve, and didn’t lay blame on Canon. They genuinely wanted to get it all working for me. When asked directly, they did concede the Canon RT mode doesn’t work for everyone. Again, my R6 still works under “Canon”,  just not “Canon RT”.




I will use Wescott gear in the studio. It works, is relatively inexpensive, and compatible. Although I’ll hang onto a 600EX-RT or two and the ST-E3 for field work, Wescott has an FJ80 flash that works with their system. Many FJ200 and FJ80 modifiers are interchangeable.

Thank you for your detailed response and analysis of your recent experience with an intermixed Westcott & Canon system!!!!!!!

Earlier this week I spent some time talking with B&H lighting specialists about the Canon interference issue. They recommended trying either Westcott or Godox. 
Because I'm a huge fan of controlling my 600EX-RTs via Canon's in-camera menu system (and not knowing if the issue lies in the Canon transmitter or in its flashes (or both)), I decided to first try using Westcott's FJ-X3M transmitter ($99).   Just came in the mail today. 

But now, in reading your post - it looks like your experience was that the (FJ-X3 to 600EX-RT) was LESS reliable than (ST-E3-RT to 600EX-RT). Ugh!   
(Sidenote: The other thing I was on the fence about the FJ-X3 is that it has a built-in rechargeable battery. Thus, you need a backup since you can't just plop fresh batteries in it; however, maybe the charge lasts tons longer than the typical AA batteries...)

I have several 600EX-RTs in my system.  Not sure I want to shell out lots of money to totally replace them to evolve to a Westcott system...
So now, I'm rethinking my strategy and will try the Godox route -- going with the XProC transmitter ($69) and then a receiver (X1R-C) for each of my Canon flashes ($40 ea). Each has a micro-USB ports for firmware updates.  

If anyone has worked with that combo, feel free to post with your experiences!


Update:  Since I posted the above, I decided to go ahead and purchase the Godox XProC (transmitter that uses the camera hot-shoe)  and X1R-Cs (attaches to each canon flash).    In my at-home experiments, I didn't lose the link to my flashes.  The longest "sleep" test I tried was 20 min - again,no loss.

I had my first shoot using them this past weekend.  In a funny/not-funny way, I found a continued use for my Canon transmitter - as a channel scanner.  I used it at the beginning of my session so I could choose a good one accordingly on the Godox. 

Overall, it was a good shoot.  There were times I was regularly active with the camera/shooting, and there were times we were setting up for the next shot and the equipment would sit idle for several minutes.  Not once did I encounter a non-recoverable link.    There were a few pics in which the flashes did not fire; however, in reviewing afterwards, most of the non-fires were when there was a delay from the previous shot and I was waking it up from stand-by mode (which can also be turned off).

Cons:  There's just more parts to keep track of and more things that can go dead over time.  Previously, I had always used rechargeable Ni-MH AA batteries and would always start off with freshly charged batteries for each client session.   Godox specifically states you should use (one-time use) alkaline batteries (or lithium) so the unit gets the full needed voltage (rechargeables have slightly less voltage).   These last a lot longer than the rechargeables.  So now, at the start of a new client session, there's the extra decision that needs to be made - keep working with the current set of (one-time use) AA batteries? Put them to the side (or toss) and start fresh? (Side note: there are rechargeable Li-ion AA batteries - something to consider moving to in the future...)

Pros:  I felt like I could once again rely on my equipment to do its job (yay!)  I always work in manual mode with my flashes.  It was super-easy to change the power on the fly to each group on the transmitter (quicker than working with Canon menu system).   I use HSS all the time - it worked great.  Setting the channel on the transmitter/receivers at the beginning of the session was very easy as well.  There's also a clear future strategy:  When it's time to buy more flashes, I will go with Godox (their flashes already have the "receiver" built in and thus over time, I'll be able to reduce the # of separate receivers I'll need.)

Other tidbits: 

  • I've turned the equipment on/off in all sorts of orders (camera, transmitter, receivers, flashes) and haven't encountered any issues of "has to be turned on in a certain order to work".
  • Some forums have indicated concern that Godox manuals are not helpful. I found them decent enough to address the vast majority of my questions (a lot of the set-up you can figure out if you've previously worked with ocf). Googling answered the rest of my questions.
  • Some forums have indicated that the transmitter gets easily scratched to the point it gets unreadable. I can see the possibility of that so I searched for a cheap trimmable screen protector. Amazon ones had bad reviews.  I ended up going to JoAnn Fabrics and (in the interfacing section) buying just a foot of 100 Vinyl Fuse - Gloss Finish ($8.49/yd).  It is very thin (~ 4gauge), easily cut with regular scissors, and has just a tad bit of stickiness on the one side (that, and static keeps it on the screen. No tape needed!). Unnoticeable when the transmitter is on.  No worries about "bubbles", etc like with regular screen protectors.  If it starts curling up over time, I'll just cut out another square from my stash and replace it.  Doesn't seem like it will leave a residue.
  • Some forums indicate it's a pain to update the firmware on the Godox (at least it's doable without having to send the equipment in!). However, I also found out that new equipment you buy has already been updated to the latest firmware (up to that point in time).  (You can verify the current firmware version on the equipment).    If you ever do need to update, the firmware files are on Godox's website.  To use them requires downloading them, uncompressing/unzipping them,  connecting the Godox equipment to your computer, and executing the update. 

Final thoughts (for now!): 
So far, so good -
The Godox still uses the same 2.4 GHz system that the Canon does, but seems like they do a better job of maintaining the communication (at least for now - who knows if they too will have problems in the next few years as communication devices continue to evolve...)
I did have to fork out a few hundred dollars for this solution (2 transmitters, 4 receivers); however, it was still cheaper than almost any other solution I could think of.
Finally, there are indeed multiple paths forward out there to achieve a reliable flash system.  Hopefully my (singular) experience can serve as a useful data point on the journey   🙂

Godox has a good flash system, just be aware that they do not provide support. Adorama does under the name Flashpoint. Having called Westcott, their first, second, and third line support was excellent.

although my personal experience with the FJ-X3 was not quite as reliable in areas with heavy Wi-Fi interference as the ST-E3, the Canon system is so unreliable that the ST-E3 is unusable at the studio. For me, the main issue is the Canon frequency and protools, in combination with new Wi-Fi hotspots. A third party use of the same protocols does not, unsurprisingly, work any better.

the fact that Wescott works wirelessly for 95% of shots, and does not disconnect means I now again have a workable solution, and have more power. Just disappointing as the Canon system is a good one.


This thread as well as one I started on PPA's "The Loop" confirm that this is a problem shared by many without an identified solution.

My own testing eliminated all of the suggested cures including batteries, channel switching, code changing, turning off my home wifi, and more.  In my home, and at some customer sites the problem is 100% repeatable rendering the radio features useless in those environments.

I took the Speedlights to the park and they worked perfectly for more than an hour without dropping the link. 

I used my iPhone to check for possible wifi competition by going to "Settings>Wifi" which shows all available wifi signals.  At home I get 5 or more plus my own 3 wifi access points.  In the Park I had only one.  After I left the park I kept my speedlights on and linked and also kept my iPhone on and displaying the available wifi signals.  As long as the iPhone showed no other wifi sites the speedlights maintained their link.  But when I got back to the city and the number of signals increased, the speedlights lost their link in a matter of minutes.

San Francisco is probably a challenging environment.  It is something like the second most dense city in the US and there are a LOT of people who have wifi in their homes with an increasing number of appliances having wifi as well.  So San Francisco is probably more signal dense than most places, too.  But my guess is that the problem is going to spread to other cities as wifi becomes more common.

I spoke at length with CPP support and while they tried mightily they had nothing to offer and nothing in their database that confirmed the problem.  The rep said that they get very few speedlight complaints and nothing like this on record.  We agreed that sending the speedlights in for "repair" would probably be both expensive and fruitless.

Fortunately, for most of what I do the IR triggering works so I'm not out of business.  But that isn't why I spent the extra money to go "top of the line" with Canon RT.

I would love it if Canon came up with a fix.  Short of that it would be MUCH better if you could reset everything from the master unit whether Speedlight or ST E3 RT.  Having to run around to reset the slave units isn't reasonable.

I will continue to pursue this with Canon if I can figure out how, and will update this thread if I learn anything new.

Thanks to everyone who posted!

Bob Davis, who is a "Canon Explorer of Light," uses RadioPopper when the RT system fails: "...when the radio system built into the Speedlite 600EX-RT isn't quite adequate."  So if CPP doesn't know about the issue, their head is in the other words, their head is in the sand.  The YT video below is from 2013.


fyi:  I talked with the RadioPopper folks to cover that base as well, and their system is NOT compatible with ST-E3-RT ... (only up to ST-E2)...

That cannot be right. So many complaints and those saying they have called support, and even sent in their flashes. Either a coverup, or serious incompetence. I tend to go with the former, as my other interactions with Canon support have been very positive,

good example of testing. For me, I tried all channels and several ID combinations.

Westcott had some insight. They said some WiFi systems will occupy the entire spectrum, or the remaining spectrum, particularly if there are competing systems. In some cases, their customers said no channel works in the RT protocol, Canon or Westcott. They told me they have few, if any problems on their own protocol.

as mentioned before, interference is a difficult problem to solve,  however, the Canon protocol seems unable to recover without a complete reset of all devices. Speculation: When a factory firmware update is required, and may disable compatibility with other units without firmware updates, Canon may have elected to ignore the issue.

Canon should make the radio antennae removable on their systems so that when wifi standards expand to new channels, perfectly good flashes don’t get bricked wifi-wise.

i used my system at the same location for years, and they were flawless until last year. I noticed, too, when I changed my home wifi.

meanwhile, two years ago, canon quietly releases a new st-e3-RT…with no real explanation to the difference…



The new version of the ST-E3-RT is cheaper, enables a few new features like wireless second-curtain sync, new FE memory mode, and support for low-power “micro flash.”

Only the newer EL flashes can update firmware via EOS series models released in 2014 or later so unless Canon wants to do a recall, like with the 600EX-RT, then it's going to be awhile.

Canon offer an upgrade from the original ST-E3-RT to a version II, but over in Europe they charge around $100 for the mod. I'm quite sure this will NOT solve our issues but this price would seem to imply that a simple firmware upgrade is not possible with these units, even on an opened unit by Canon. As the 600EX-RTs behave in the same manner as the ST-E3-RTs I'm also assuming (due to the lack of other reliable information) that they incorporate the same RF related circuitry and firmware. If this is correct, a simple firmware update is probably also not possible.
If the above is correct, to resolve these connection issues we'd most likely be talking about the replacement of circuit boards. Canon wouldn't want such a problem to get too public because this might turn into a rather expensive recall. I'm not holding my breath...

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