Yongnuo YN 560 III optical slave not working?

My apologies if this has been answered elsewhere before, but searching the site has not given me an answer to my problem.

I'm a Canon 7D user, and I have the 600 EX RT flash as my main flash on location. I've gone ahead and purchased 2 Yongnuo YN 560 III flash units for additional lighting. I knew going in that the wireless functions wouldnt work between my Canon flash and the Yongnuos, but all I wanted was to use the 560's for as optical slaves to go off when I fire off my Canon.

I tried all morning trying to get it to work in both s1 and s2 modes with no success, and the manual isnt really helpful at all. What am I doing wrong here? As an optical slave, it really shouldnt matter what flash is setting it off, a flash is a flash. How can I get these Yonguos to play nice?

They do not fire at all, they just emit a high pitched whine when I take a shot. Oddly enough the Yomnguo flash isnt even working if I hit the test button.

Any help would be appreciated.

Tim The Photo Guy wrote in post #17722455
... As an optical slave, it really shouldnt matter what flash is setting it off, a flash is a flash.

Well, assuming there are no pre-flashes. If your 600EX-RT has wireless communication functions set, it's setting off multiple preflashes, which can screw up the timing. Make sure it's out of wireless master/slave (optical) modes, and that it's in M if you want to use S1 or eTTL if you want to use S2.

However...

This would indicate that there's something wrong with the flash, not the slave. The first thing to check is that all four of the batteries are fully charged and in good health, and inserted the right way. The whining sound you mention is typically when the flash is charging (i.e., drawing enough charge from the batteries to fill the capacitor). On my YN-560, when the PILOT button/light is green, it's recharging, and I can't fire the flash until the button/light is red.

It's also not beyond the realms of possibility that you got a bad unit.

Is it one or both 560 III that are not working? I take it that neither is working, when you place them as required for S1/S2 to work.

If you hear the whine when you take a shot, that suggests that they are in fact being triggered, the capacitor is depleted, and the recharge circuit recharges. If no light is emitted, it seems unlikely but possible that both xenon tubes have failed. And that is a common problem with these flashes.

If the Test button does not provide a flash on release of the button, then the 560 III needs servicing.

How does each flash behave when mounted directly on the camera?

Thank you Inkista & Cliveyboy for the help!

What I learned: the one Yongnuo definitely doesn't work and is being returned. The other *does* work, but not with my Canon 600-RT, not even if I set the flash to manual. This is a bit frustrating as I had intended to do some portrait work outdoors with my 600 being the main flash, and the Yongnuos being accent lights but indoors it works fine with my Photogenic lights as an optical slave. So there's that.
I'll just have to figure out a plan B for outside work.

Thanks again!

Tim The Photo Guy wrote in post #17724841
The other *does* work, but not with my Canon 600-RT, not even if I set the flash to manual. This is a bit frustrating as I had intended to do some portrait work outdoors with my 600 being the main flash, and the Yongnuos being accent lights but indoors it works fine with my Photogenic lights as an optical slave..

I presume you have:
7D + 600EX-RT on top (with the 600 in Radio Transmission mode, NOT optical transmission mode and Slave, not Master)
and a remote YN560III up to 12ft/4m away with its receptor window rotated to the camera and in S1 mode and sleep mode effectively off.
That should work. Could ambient (sun) be swamping the detecting sensor? The difference between excessively bright and ever-so-slightly more-excessively bright may not meet the change criterion.