Flash Broken,..... need help!

[dcheung]

Okay, so last weekend when I pulled my 420EX out of my bag, it started to

malfunction. The body I use is a 20D. Basically what the flash is doing is

during the first flash (pre-flash) where it determines how much power to use

for the main flash, the 420EX relases all it's power. So during the actual

flash, there is no power and so the camera picture taken is dark. When I

press the exposure lock button,the flash releases all it's power. When I put

the flash to slave mode and press the depth of field preview button, the flash

releases all it's power.

 

I borrowed my friends flash to test if maybe my camera is busted but my

friend's 420EX works perfectly so the problem has to be with the flash.

[dcheung]

Does any one know the electronics or communication specifications for the 420EX? I need to find out which communication line is broken so I can open it up and fix it.

 

Is this a comon problem for 420EX? Have anyone encountered or heard of such an issue before?

[andy_van_eynde]

And how do you know the problem is in the circuit of the flash and not your 20d?

 

Did you also try another flash and/or body

[PuppyDigs]

Yes he did (read the first post).

[maxasst]

In the past when rushing to take a picture, I didn't mount the flash fully forward on the hotshoe of the camera, and the resulting pictures were all full flash. Maybe there is some mechanical problem with your flash's base not allowing it to go fully forward, so try comparing how it mounts compared to how your friend's 420ex mounts. Good Luck.

[andy_van_eynde]

Oops...did not see that last paragraph!

[pturton]

Not the circuit, but exploded views and parts list of the 420EX and other Canon products in PDF format: http://www.f20c.com/stuff/canon/partslist/

[mark u]

You will need to have a lot of electronics expertise to deduce exactly where the problem lies - it could be in the wiring from the foot to the circuit boards on in one of the circuit boards itself. If you really want to try this, rather than either paying for a Canon repair or getting a new flash, then you will find the following resources useful:

 

http://eosdoc.com/manuals/?q=EX-M-TTL

 

(shows which contacts handle E-TTL and TTL signalling)

 

http://members.misty.com/don/donflash.html

 

(a lot of information about simpler flash units than a 420EX which will help in deducing what the 420's circuits are doing)

 

Be sure to read the guidelines about dealing with the high voltages that can build up on capacitors in flashguns.

[dcheung]

Yup, I tried to see if maybe the flash wasn't sitting properly, but it was sitting all the way into the shoe. I also tried the flash on my friend's 10D and the same problem occurs.

 

Mark, thanks for those links.

 

I have considered canon repair shops, but I'm guessing it will cost more than 100 bux to fix it. What do you guys think? Also, how do I find out where the repair shops are? I'm live in Edmonton, Alberta, Canada.

[mark u]

1 800 OK CANON