550 EX defaults to TTL on 20D

After many months of working normally, my 550 EX won't go into E-TTL

mode on my 20D--not matter what I do. I put the flash on my Elan 7

and it goes back to E-TTL. Take it off, put it on the 20D, and it

goes back to TTL, and switching modes on the flash unit does not bring

up E-TTL. All I get now are blasted frames. I've cleaned the

contacts, fiddled with switches, etc. No E-TTL. Thoughts?

Well, seems to have been a *really* dirty contact--required scraping, not just solvent. Works now. Thanks anyway.

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Check the shoe is not loose - it took me many months to work out what was wrong on a 1D - kept thinking a clean had cured it when all I'd done was strike lucky/shake it about a bit. On the 1D one can tighten the shoe by removing a very thin spring cover under which are four cross head screws - don't know about the 20D