I have a 600EXii-RT problem that I can't figure out. I changed the batteries and now the unit powers on normally, but won't flash, even with the test button. I had been using it for a few hours prior to the battery change and it worked perfectly. No settings on the unit or my camera (5DM4) were changed during the battery swap. I did try replacing the batteries again (they are new and fresh) but to no avail. There are no error messages active on the flash or camera, and the ready light stays red. The flash unit is a few years old, but has less that 500 flashes on it, very seldom used. Any ideas would be greatly appreciated.
Hi Dakota59 does the pilot light turn on when the speedlite is turned on. What kind of batteries are you using rechargeable or Alkaline batteries. I also own the 600EX II-RT and found the flash doesn't like rechargeable batteries due to the lower voltage. Rechargeable AA batteries only put out 1.1 or 1.2 volts while Alkaline batteries put out 1.6 volts.
40D, 5D IV, EF 16-35mm F/2.8L III, EF 24-70mm F/2.8L II, EF 28-135mm F/3.5-5.6 IS USM, EF 50 F/1.8 STM
430EX III-RT & 600EX II-RT
Thanks for responding deebatman316. I am using alkaline batteries, all new and fresh. And if by pilot light you mean the flash ready light, yes, it is on. It doesn't go green at start up though like it used to, just stays solid red. All other functions work and the display looks like it should be flashing. I am very confused.