cgardner Offline Upload & Sell: Off
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The contact related problem usually results in the 580exII thinking its been told to change to legacy film body mode (TTL) and firing at full power because it never gets a command to turn off: net result, gross overexposure. Not what seems to be happening here.
The normal sequence of events in ETTL mode is for the camera to fire several command and exposure metering pre-flashes between the time the shutter is fully pressed and the mirror and shutter open. You say increasing FEC results in the flash "blasting away" which seems to imply the main flash is firing, but If you can see the flash in the viewfinder its the pre-flash you are seeing, not the main flash.
The first step would be to carefully review all the flash menu settings (reset to defaults) and check the flash for sticking contact pins, particularly the one that is centered which is used to transmit the "fire main flash" command.
If flash menus are set to defaults and the pins retracting and extending correctly it may be a circuit board problem. That's the second most common complaint with the 580exII I've seen mentioned in the forums.
The worst case, sending the flash in for repair, isn't too painful. Canon fixes them for a flat rate of about $130, less if you are a CPS member. Since defects in the 580exII are so common if you complain a bit they might fix it for free if out of warranty.
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