Problems with the 420EX

I have a Canon 420EX Speedlight and when I take a picture it flashes at the wrong time. When I push the shutter button its either flashing too late or too early i cant tell. when i look through the viewfinder i can actuall see the flash going off. I took some shots into the mirror with the flash on at 200 shutter speed and my flash was dark. Is my flash repairable??

It's normal for you to see the flash going off through the viewfinder. What you are seeing is the ETTL preflash from the flash. Other than that, are you flash pictures coming out too dark? Also, what do you mean when you say the the "flash was dark". Do you mean that it didn't fire or do you mean that the picture is too dark? Do you have any sample pictures we can look at?

If you are shooting into a mirror, that will cause all sorts of problems for ETTL. The preflash will reflect back at the flash and cause all sorts of weird exposures.

It won't cause all sorts of weird exposures. It'll just cause the image to come out pretty dark due to the direct reflection of the flash in the mirror.

Could it be that you have your camera set to second curtain sync?

the flash is firing when the shutter is closed. the flash flashes like normal but you can not tell the difference from when it is turned on and its turned off. its like its firing at the wrong time

oh and when i took a pic in the mirror there was no evidence of light whatsover coming from the flash but the flash fires like it normaly would when it worked. its like it is off sync

Try this. Remove the flash and clean the hotshoe contacts of the flash and the camera, then mount the flash back on the camera. Set your camera to "P" mode and turn on your flash. Check to see if there is a lightning bolt in your viewfinder. If there isn't, it indicates that the flash is not communicating with the camera and a possible problem with the flash. If there is, take a picture of something very close and see if the lightning bolt blinks for a couple of seconds after the shot is taken. If it does, that could also indicate a problem with the flash.

Remove your flash and pop up the internal flash and follow the same procedure above. If there is a lightning bolt in the viewfinder but does not blink after taking a picture (in other words, the flash picture is fine with the internal flash), then your 420EX is probably malfunctioning and should be looked at. Try a different external flash and see if the problem still exists. If so, then it may be the camera instead.

If you are having the same problem with your internal flash, then it is probably your camera that's at fault.