I have noticed several users with non functioning shutter buttons, so I thought I would add this for those who like tinkering.
There is another method about pouring rubbing alcohol into the battery compartment that cleans the contacts of the shutter button. I find that as just a temporary fix. If you think about it you really have nothing to lose. It doesn't work now, you can always pack it up and send it off to be fixed. Ok, so here goes nothing.
First off, I used this set of three videos for the basic disassembly.
All 3 videos can be viewed under this subscribers video page.
I thought I would add a few notes on the differences from the 30d to the 40d(may be same on the 50d). I didn't have a camera to take photos of the individual steps. In total it will take about 1-1.5 hrs. for to disassemble, repair and reassemble. If you take your time, lay out your screws in order of removal, in groups of removal and watch the videos first. These instructions will make more sense and make the job easier.
Tools needed: Small precision Phillips screwdriver(magnetic preferable), really small precision flat head screwdriver, toothpicks(will under stand why later), super glue(don't laugh just yet), Q-tips and rubbing alcohol.
And now comes the FUN part(proceed with caution)
**Safety first - REMOVE BOTH BATTERIES TO AVOID GETTING A SHOCK AND DESTROYING YOUR CAMERA.**
1. Carefully remove all the rubber grips, use small screwdriver to lift a corner of the grips and slowly peel them off. Being careful not to touch the double sided tape.
2. Remove the three silver screws from the side USB/VIDEO cover and gently grab the rubber covers and pull straight out to remove the cover.
3. Lay the camera on its back, starting on the right side remove the 2 silver screws, 3 black screws around the lens mount(2 above, 1 below on bottom, the bottom is shorter than the top two don't mix them up), 2 shorter black screws in between the lens mount and the grip, 1 silver screw in the grip, 2 silver screws in the side of the grip next to the CF cover. Now gently pry the front face up and off. I leave the body cap in place to keep unwanted matter out of the shutter/mirror assembly.
4. Now flip the camera on it's face, remove the eyepiece and remove the screws starting on the right. Remove the 1 silver screw,
remove the screw for the Diopter adjustment(knob is slotted so watch that it goes back in correctly upon reinstallation), remove 2 black screws around the viewfinder. and 2 black short screws on the bottom edge at the corners.
5. Carefully pull the back panel w/ lcd and scroll dial on it, be careful not to pull it out to far at first. Once loose, stand the camera upright supporting the back cover. Looking from the top there will be 2 ribbon cables that attach to the back cover. The one on the right that the attaches at the bottom and can't be removed without a lot of extra disassembly, the other cable attaches on the left side of the body behind the LCD. Carefully use the flat head screwdriver to pry the lock up(the brown part of the white socket) and observe the ribbon cable. The ribbon cable has a small hole in the middle of it, use a toothpick and insert it into this hole and carefully work the cable straight out from the socket. This will free the back cover enough to continue the disassembly.
6. With the camera still up right remove the black screw on the top next to the strap attachment. Holding and supporting the camera and back cover, flip the camera upside down and remove silver screw on the side under the strap attachment and the silver screw under the shutter button and flip the camera back over and support the back cover(I used my battery to support it).
7. On the right side right under the Exp. lock button, remove the outer most ribbon cable(pry up on the brown lock and use toothpick in the ribbon hole and work it straight out of the socket as before). Now in the middle of the circuit board, there is a white square attachment block with a black wire going into it from the top cover running next to the eyepiece, carefully wiggle and pull this out(it is held in with a small spot of adhesive). Now the top cover can be carefully pried up and off(being care not to pull out the wires on the USB/Video side) carefully un-route the wires and flip the top cover over.
8. With the top cover flipped over locate the shutter button assembly, remove the 2 silver screws on either side os the shutter assembly and remove the 1 silver behind the shutter button assembly holding the ribbon cable in place. Now gently wiggle the shutter button assembly out and remove the ribbon cable from the white socket behind it. The cable just pulls straight out(no lock on this one, it is a friction socket) using the previous ribbon cable removal process.
9. With the shutter button assembly out(don't pry the actual button/ribbon cable away from the housing like in the video) using your small flat head screw driver gently pry up the bottom clip of the shutter button cover. Once loose, be careful using the steps and techniques in the video, remove the guts of the shutter button, clean and reassemble all the parts.
10. After cleaning and reassembly of the shutter button, reinstall the shutter button assembly back in to the housing leaving the cable free for the moment. Install the 2 shorter screws that hold the shutter button into the top cover. Align the ribbon cable in the socket and use the toothpick to push the cable back into the socket until fully seated and reinstall the longer silver screw that anchors the ribbon cable.
11. Flip the top cover back over, reroute the wire back into the body and reattach the top cover and replace the 2 silver screws(1 one the usb/video side and the other under the shutter button) and the black screw on the other side. Insert the black wire back into the white block on the circuit board and use a small dab of super glue(on the end of a toothpick) to hold the wire in place. reinstall the ribbon cable removed earlier and lock the brown lock by gently pressing it down.
12. Reassemble back cover, front cover and side cover in reverse order. Reinstall the batteries and give it a test run.
**If successful, grab a beer(or preferred drink), pat yourself on the back and enjoy your newly functioning camera. **
**If not, I like to use a BF hammer and take out my frustrations on the broken equipment, then grab a beer and pat myself on the back either way for a job well done. **
The legal mumbo jumbo: Proceed at own risk, not responsible for any damage to your equipment, credit given to all original sources, etc. etc.
Have fun tinkering and enjoy your the money you saved DIY.
Maybe this isn't too confusing and maybe it will be helpful to someone, somewhere, someday!
GOOD LUCK AND GOOD DAY!!!!!