As it could be an interesting topic not only for hungarians, I will try to write it in english.
The 40d bodies, as I know, have two main problems: shutter fails (this could happen even after 5000 activations…), or the main mirrors plastic frame brakes – I know 3 cases till yet, after 105000, 86000 and 50000 activations.
The official repair procedure is the change of the complete mirror box – for approx. 350 EUR – the body at this age has a value of approx. 375 -450 EUR. Not a big deal…
Why exactly by this model?
Probably because the separate mirror motor, which opens it very quick. The frame has the same “bearing” as the predecessors, and it is too weak for that forces.
What to do, when broken?
Don’t try to make more shots, because You will need the broken part for the repair. If it falls out, it’s hard to find it on the rug. (I have a friend, who has found it in the vacuum cleaner a few days later – I’m not joking. It’s a piece of black plastic, of aprox. 2×3 mm size).
Here it is:
To repair it, You will need to disassemble completely the body, to take out even the shutter. Under the shutter is a metallic frame, which keeps in the “bearings” (two semi-holes) the two pins of the mirrors frame.
(this two pictures were taken after the repair)
As the broken surface has always (in the 3 known cases were so) a sharp form on both parts, which fit perfect together, if we glue them together, we will have possibly a not too big geometrical error.
But. To make the part stronger then it was, we will need a strong glue – I use a 2 component one, made in Hungary (Uverapid 5 A+B), which needs 12 hours to get hard. The glue has a honey-like viscosity – so it can not be used between the surfaces.
Between the surfaces I use a cyan-acrilic glue – but very important, that the liquid one (not gel). It works very quick, and it’s not strong enough, but I use it only to position the two parts in the correct way (as they were before).
At first, parts must be degreased (I use a special petrol from the pharmacy).
The submirror must be protected with some adhesive tape.
Then put a drop of glue on the surface and try to find it’s original position. You have aprox. 2 seconds. Then press them together. My fingers always are fixed to the parts…
As You see, the outher surface is not perfect. Now, You have to cut the unecessary glue, and with the knife you have to make the surface a little bit rough, for the other glue.
Then put the glue on the broken parts – be carefull, not to block the submirror.
Last time I’ve done this in two steps, so two thin layers of glue.
The most beautyful job is coming now: to put the mirror into his place.
Not enough space
Yes, there is not enough place, the box was not designed for such operations. But if You have enough patience, You can manage it. I use for this operation a small flat screwdriver between the mirror box and the mirror frame.
Don’t forget to put back the two springs on the mirrorframes moving pin – you can do it with the same flat screwdriver.
Be carefull, the mirror can be moved up and down only in certain positions of the mirror motor and the shutter mechanism – otherwise ther are some pins in the mirrorbox, which will block the mirror.
There is another problem too. The glue has a very shiny surface, which could produce unwanted reflections. I have some acrilic paint (4 EUR for a small bottle which I will use probably in the next 80 years), which is black matt, plus a small brush.
You can paint it in it’s place in the body.
(You can use the same paint even for older lenses etc.).
Now You have only to put together the body, and to check if it works.
Last problem: AF
AF (autofocus) will be probably not ok. Frontfocus or backfocus can both appear.
Of course, as we took out the mirror, and even the frame is not exactly like was before …
There are 2 ways: you bring the camera to an official Canon servicepoint, to adjust the focus electronically, through programming. In Hungary this would cost approx 50 EUR…
The other way is very barbarian, but it works: You have to modify the position of the submirror. By the good old 300d this was very easy, as it has an adjusting excenter. The 40d has fix bumper-pin.
The control of the AF accuracy is very simple. Put the camera on a good tripod, use a 50 mm F1,4 lens on F1,4 aperture, use an adecvate target (at 45 grade, from 1 meter) activate the AF, then turn to liveview-mode, magnifying of 10x and if You have to modify to get the right focus, the body is not perfect. You can also take a picture, on the picture You will see the same, as in live-view.
The following method you have to use only, when you have no other possibility, because it could happen, that you will damage the mirrors definitely.
If You have front focus
You have to take of material from the bumper (the palastic from the submirror). With a sharp knife, step by step, between the next step a short control.
At first You have to put more material on the bumper – use the 2 component glue, you will need 0,2-0,4 mm. After the glue is (semi-)hard, You can cut it at the desired size.
Remark (31.01.2015) For a few years I use the SPT software to adjust the AF system for 40d cameras, so I don’t make this “mechanical adjustment” anymore. For a quality work you have to do it with the software adjustment.