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.
