Odd flash problem.

I have 2 flashes, 420EX and 220EX. Noticed the other day with the 420 the flash is not showing up in my pics - I see the flash burst in the view finder but my target is not "flashed". Take off the 420 and put on the 220, presto. Changed the batteries (thinking maybe it was having an effect but no difference.) Any thoughts? Same results on 3 bodies, 5D MKI and II and 60D. Its as if the 420 is firing too soon. Seemingly an issue with the flash?

Ed

It seems the 420EX is processing the 'preflash' command, but the main firing trigger is not working.

Try to

1. use the Test fire button to fire the flash manually, then also try to...
2. use a short thin wire to bridge between the contact on the edge of the hot foot, and the center (Trigger) contact on the bottom. to fire it

Ability to fire with one but not both methods gives a strong clue about what broke.

Wilt wrote in post #18372611
It seems the 420EX is processing the 'preflash' command, but the main firing trigger is not working.

Try to

1. use the Test fire button to fire the flash manually, then also try to...
2. use a short thin wire to bridge between the contact on the edge of the hot foot, and the center (Trigger) contact on the bottom. to fire it

Ability to fire with one but not both methods gives a strong clue about what broke.

Tried both methods, flash fired with both. Also called Canon tech support, he suggested doing a "reset" of the flash - turn unit on, remove batteries, push and hold pilot button for 30 seconds (discharge capacitor). End result the flash still does the same thing.

Thank you Wilt for the response!

Suspicion that any pre-flash drains the flash unit so much that it has nothing left for the main flash!

You can manually fire with Test button or shorting the contact pins, and in that situation there is no preflash occurring.