Problems with 550EX speedlite

[VizualCreep]

I've got a 550EX speedlite that's very suddenly not working properly.
It only fires on half the shots I take and half of those shots it fires either too early or too late (unsure which but images are dark).

Another oddity is the flash used to read what focal length my lens was at, display that focal length on the LCD and then zoom accordingly. Now the LCD simply shows " - -mm" and does nothing!

I've got a wedding to shoot THIS EVENING! Has anyone had a similar problem that can shed some light?? I'm in panic mode. I think I'll be using my fully manual backup flashes tonight.

Thanks very much all!!

Aaron

[tim]

Welcome to POTN :)

Make sure the flash head is pointing directly forwards, not down a little, that can cause the blinking. As for being out of sync make sure it's *properly* on the hot shoe, and give the contacts a wipe with a dry cloth or a pencil eraser. Other than that you'll have to switch to your backup.

[Tragerman]

I've seen the same trubs with my Sigma 500 DG Super. A simple wipe of the contacts on the flash foot and the hot shoe was all it took. Frightening in the middle of an event, though. Having the flash securely mounted with all contacts clean is critical to the computer communications between the flash and the body. Distance, focal length, fire, quench and other data and commands happen in very short order. Even a little static electricity can interfere. If after you've cleaned the contacts you still experience a problem, make sure both devices are turned off. Remove the flash. Gently wipe the contacts again and replace the flash. Turn on the camera. When it's up, turn on the flash. Hopefully all will be well.
Good Luck,
Mickey

[etaf]

do you use with a off camera sync cord - i had to disassemble my sync cord and tighten some little screws which fixed the plate and plastic together - thi shad a simular problem