Well, well, well... It took the demons five months to catch up with me, but find me they did. I was up at the Beargrease Dogsled Marathon two weeks ago with 4 RF-602 receivers and 2 RF-602 transmitters. The lights came on for all devices, but they simply wouldn't talk to each other. At the time, I was at BARC Net Control (Ham Radio station coordinating communications between checkpoints and HQ), so there was plenty of 2 meter traffic, and my laptop showed several wireless access points (2.4GHz is common). And yet, I couldn't get the either transmitter to work with any of the receivers. I replaced batteries, changed batteries, switched channels, etc... nothing.
The devices remained in their catatonic state even when I returned home. Last night, after they had been sitting on a shelf for almost two weeks, I got them out again. Still no love. Finally, I took the battery out of one of the transmitters, flipped the channel switches again to see if something was just off, checked the battery compartment for any obvious breaks in wiring or corrosion. Finding nothing, I popped the battery back in and gave the test button a half press and all four receivers' LEDs turned green! WTF? Sure enough, they were all talking again like one big happy family.
So, I turned my attention to TX #2. Half press of the test button and still the receivers ignored it. I took the battery out for a good thirty seconds or longer, popped it back in and Shazaam! Everyone is talking again. I still had the older batteries from Beargrease. So I popped them into the transmitters and things still worked.
Moral of the story... If things stop talking to each other, take the batteries out of the transmitters for 30 seconds or longer. I'm going to store mine without the betteries in the from now on. Yongnuo needs to add a dedicated off switch to the transmitters like they have on the receivers.
I'll give them another test this weekend to see if I can still hit over 400 feet like I did back in September.
P.S. Beargrease was a virtual Nikonfest. All the DSLRs I saw (except one) and most of the P&S were Nikon. The one DSLR exception? The Canon used by the guy from the Associated Press.