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I bought my Canon 600EX speedlight 3 months ago, I’ve been using it with my Canon EOS mark iv and the Canon speedlight transmitter ST-E3-RT, until now everything went well, suddenly it just dropped link; I thought it was the batteries so I changed them, worked for 3 shots and again dropped; it’s turned on, and everything seems to be working, suddenly it unlinks and the flash won’t go off; I reseted all the settings, twice! it works once or twice and again nothing, changed the Chanel, just in case, same thing happens, works 3 shots and I have to turn it off and on again for it to link again and for the next 3 shots, then again it unlinks.


Product Expert
Product Expert

Hi mariacorcuera,

Thanks for checking in with us.

It might help to try doing tests at different locations, just to confirm that the issue is location specific. It might also help to power everything down, clean the hot shoe area on camera and ST-E3-RT, and then try again.

If problems persist, try using one of your flashes on camera as the transmitter. Then try that with another flash. That will help us determine if the issue is specific to the transmitter or to select flashes.

Different locations were exactly the same, the link dropped suddenly... I also cleaned them both and the same.

As for the flash, I don't have another flash to try it with

Cleaning the hot shoe is a ridiculous suggestion, the hardware I have (two EL-1 flashes and the new St-E3-RT ver. 2) are brand new out of the box, and the link is dropping regardless of the hot shoe as the flashes are on the supplied stands. So the contacts from the flash are on plastic, not even connected to the Camera.

Clean the hot shoe! WHAT? That's like the doctor saying take two aspirin and call me in the morning. I have TWO brand new Canon El-1 flashes, a brand new ST-E3-RT Version 2 trigger, and the flashes will drop the link. Nothing is even connected to the hot shoe, except a plastic stand for testing this issue. 

Please start a new topic.  The thread you replied to is for the 600-series speedlites and original ST-E3-RT version.


Camera: EOS 5D IV, EF 50mm f/1.2L, EF 135mm f/2L
Lighting: Profoto Lights & Modifiers

It's not the ST-E3-RT (version 1 or 2) transmitter, as I have both of these and when you turn off the transmitter, the LED lights will turn off, then turning on the transmitter again, the LEDs on the two EL-1 flashes will turn green. Turning off the transmitter for about 10 minutes, then back on, I found one of my EL-1 flashes lost the connection, so in my opinion, it's not the transmitter, how could it be when it was off?


Ooops, sorry, I also meant to say that using two each Canon EL-1 flashes along with my older 600EX-RT flash, all threse have the same issues. 


It's quite the problem for Canon at this point. I have two of the brand new EL-1 flashes, and one of the older 600EX-RT flashes, and they all have a problem staying connected. Upon further investigation, it's not the ST-E3-RT with the problem because I turned off this transmitter, and turned it back on several times to see if the LEDs were still green, and within about 10 minutes, one of the EL-1s dropped the connection, so how can this be the transmitter problem? Based on my tests, it's the flashes that are dropping the connection, and we all know it's RF interference, could it be the new WiFi-6 wireless access points around the house and commercial venues? There are other posts that suggest Apple HomePods are the issue, but these items are not in my house, so I cannot confirm or deny these are the conflicting hardware. I do have the new WiFi-6 access points from UniFi as my "MESH" Wi-Fi system in the house.

I made some other tests by purchasing the "sock" that covers the flash and sort of shields it from the RF interference, but this causes more grief because you are essentially now limiting the ability for the transmitters to communicate to the flashes. These are not the solution either, as the link was still dropping. Ugg...
So I did some other tests, and I bought the ($80 USD) Godox transmitter X-Pro II C, and purchased two of the ($40 USD) Godox X1RC receivers for mounting to the Canon EL-1 flashes. Using this configuration, I NEVER lost the link from the Godox transmitter to the Godox receivers, EVER. I let this run for hours, made several tests, used my Canon R5 in different configurations, manual mode, ETTL, and the connection stayed solid, I never lost the link to the flashes.
That being said, there are plenty of posts throughout the Canon forums where this is a huge problem for Canon, and you hear suggestions from Canon support: "Try changing the batteries". Are you kidding me, that is ridiculous, they have nothing else to suggest because deep down they know that interference with all of the "Internet of Things" on WiFi-6, and the 2.4 GHZ band is full of traffic. So why does the Godox (Chinese made) hardware stay connected?
Unfortunately, this means a few more dollars for additional hardware, more AA batteries, but at least the connection is NEVER dropped, and I do not have to power cycle the Canon flash and Canon transmitter. The other downside to Godox transmitters & receivers, you don't get all of the features that Canon has to offer, but in reality, do you really need to have the flash at less than 1/128 power? I say this because the Canon transmitter and EL-1 flash can be set to 1/8192 power, and the Godox can only be set to as low as 1/128 power, which is not a big deal in my opinion. You do however get some pretty cool features in the Godox transmitter, you can turn off any single flash by double tapping one of the 5 group buttons, a useful feature that is super fast.
Deep down, I really think Canon has a problem that may not even be fixable though firmware, it's most likely the frequency that Canon uses that is conflicting with nearby RF devices. In my opinion, why Canon does not reconnect automatically instead of power cycling the hardware is beyond me.

You are a living angel! Thank you so much I have spent so much time fighting with 3 600EXII-RTs and my st-e3-rt too trying to solve this before wedding season picks up.

I keep everything Canon but after doing every troubleshoot possible went back to check the forums one more time and saw your post. You made my month!