My second time fixing a problematic EOS mirror (the first time was on the Rebel/300D replacing a broken pin).
Problem descriptionEverything works fine, apart from pressing the shutter the whole way. Then nothing is heard at all, the camera just goes into BC-flashing mode. This is true even without a lens and with a good battery (use the battery check function). Pressing the shutter again just "rattles" the shutter curtain but the mirror does not move. Also, there might be a curtain rattle when starting the camera.
For other problems, see this page.
Probable causeThe electro magnet moving the mirror assembly has jammed. This seems to happen quite easily, especially if the body is not used for a longer period of time. Other EOS models are also prone to this, including the EOS-1 and EOS-1N.
Warning: I do not take responsibilty if you mess up and destroys anything, proceed at own risk.
1) Remove the film roll. Leave the camera on and remove battery container or grip from the body.
2) With a Phillips #0 screwdriver, remove the long screw from the film roll compartment.
3) Remove the lids for remote trigger and flash. Red arrows below.
4) One at the time, remove and then screw back one full turn (!) the screws indicated with green arrows.
You do not want to remove the whole panel, just make it as loose as possible. If you do remove the panel, the latch mechanism with two buttons, two springs and two metal pieces might go flying. If you manage to do this anyway, see bottom of page.
5) Now remove the three identical screws indicated by red arrows. Also remove the bottom screw between the lens mount and tripod attachment indicated by yellow arrow. Note that this "yellow" screw is ever so slightly longer then the other three. Don't mix them up!
Also remove the cap over the lens mount if it's still on.
6) Now carefully hinge open the front panel. Start by the battery/grip end and move up and hinge away. Take care not to destroy the plastic that goes under the panel by the door mechanism that we loosened earlier. Also, make sure the aperture check button and rubber does not go missing, they're loose!
7) Now the culprit is located, it's the white little square plastic box. Tap it firmly with something hard a few times, but don't over do it. :) Tap it straight on as the arrow indicates.
8) Slide the battery/grip back in and hold it in place, the camera should start like normal since we left it on. Try the shutter, the mirror should fold away and everything work just fine. If not, try some more tapping. It it still won't work you might get lucky cutting the white box open and put some electronics cleaner in there. Cut VERY carefully, you do not want to hurt the coils. See if you can get the magnet in the coil moving.
9) Did you succeed? Great! Let's fire the shutter a few more times so the magnet gets some exercise and then let's put the camera back together!
If not, bummer! Guess you're out of luck. :(
10) Take a look at the aperture check button. The red arrow rubber thingie must clear the green arrow circuit-board. This is quite fiddly and the rubber and button easily falls out of the front panel.
11) Start by hinging the front panel into the latch panel, then let it fold down partly over the lens mount. No force should be necessary here.
12) With some tool press the rubber away from the circuit-board while hinging the front panel the rest of the way. I used a small flat screw driver but some piece of plastic with soft edges is probably preferred, don't scratch or bend that circuit-board!
13) Now put the screws back in but don't tighten them until all screws are put in so everything align correctly. Remember that the bottom screw is slightly longer than the other three front screws! The really long one goes in from the back. Check that the lens release button works. It should lower the little metal pin next to it.
14) Go out and shoot some film!
If you happen to remove the latch panel, this is how it should go back together. Note that the front panel can't be attached. The little silver metal part hinges on a very short pin close to the camera top. The long spring should rest close to the flash connector. Keeping the door closed and latched keeps the parts in, until you accidentally squeezes on the door that is...
On top of the metal parts goes the little spring on the pin, the slider and finally the slider button. Then the panel.
Some links that might be helpfull:
Part listing for the EOS-3 with exploded views (however the long screw from the film compartment did not show itself very well here, took me quite some time to figure that one out):
Link 1. Link 2.
(parts lists for other models might be found here)
English PDF-manual for the EOS-3.
Other solutions for the BC-error.