Older Canon EOS cameras suffer from a problem with sticky shutters. If you examine the shutter of almost any EOS more than 10 years old or so, you will find a black sticky deposit on the shutter curtain. The image below shows a typical deposit
In this case the goo has not yet built-up to the point where it interferes with shutter operation, but it will before too long.
The deposit can be cleaned off with care, which will temporarily restore shutter function, but the problem will return shortly, and the shutter will need to be cleaned again. Obviously repeatedly cleaning a delicate component like the shutter curtains is fraught with risk, and sooner or later, this will result in permanent damage to the shutter. Replacing the shutter in any SLR is an expensive operation involving quite a bit of labour, and most cameras with damaged shutters are discarded as write-offs. Obviously this is an undesirable situation. Don’t despair however, the problem has a solution, which anyone can apply with a little patience and care. This page illustrates fixing this problem on an EOS 750 camera. If you have a different EOS, the procedure will not be too different. Check my other pages for the particular camera you have, I may have already documented your particular model. The particular specimen illustrated came to me with a stuck shutter problem, and some apparent debris in the viewfinder which reset on mode switching and power-up, and the cause of this fault is also illustrated.
- What Causes the Problem?
- Disassembling the EOS 750 to Access the Shutter
- Door Latch
- Front Cover
- Bottom Cover Removal
- Latch Components
- Camera Tour
- Flash Circuit
- Removing the Top Cover
- Preparing to Separate the Film Transport
- Rewind Gear
- Removing Cage and Shutter
- Disassemble and Clean the Shutter
- Re-assembly Notes
What Causes the Problem?
This is not a particularly difficult camera repair, but before we can fix this, it is important to understand the cause of the problem. This is a picture of a partially disassembled shutter. If you look below the deposits on the shutter blades, near the bottom edge of the shutter assembly, you should see a rectangular block, with an oval protrusion. It’s a rubber buffer, and it is the source of the problem. Basically, it has started to decay, and the black goo is pretty well all that’s left of it. To fix the problem permanently this has to be removed.
You might think that removing this buffer would have a serious adverse effect on the operation of the shutter, but in practice it makes no difference.
It’s function appears to be to reduce the stress on the shutter hinges as the blades come to a rapid stop, but the effectiveness of this is doubtful. If you are worried, you could of course glue a piece of rubber cut from an old rubber mat or something to replace it. (In fact an old inner tube would be ideal. The type of rubber used is very good at absorbing shock.) Make sure that if you do, that you don’t choose a replacement which is going to perish quickly, such as an elastic band! In fact breakdown of doubtful rubber components is a common cause of camera failure, see my other pages for examples. To get at this you have to partially disassemble the camera. I have taken care to ensure that the amount of disassembly is the least that is required. There is quite a lot of stuff inside the EOS cameras. Most other OES’s using the same shutter are less complicated, and you may be able to adapt this for other models. Disassembly of other EOS models (Including the EOS 600 / EOS 630) are illustrated elsewhere on this site, and will be added to as I obtain samples requiring maintenance.
Disassembling the EOS 750 to Access the Shutter
Before you start, you will need some tools. Thankfully Canon have elected to build these cameras using fairly standard fasteners, and all the tools should be easy to find. You will need some jeweller’s cross-headed screwdrivers. These should include sizes ‘0’ and ’00’. A fine tipped soldering iron is also required, of 15 to 25 watts rating should be fine, a temperature regulated iron is perfect.. (Don’t use a portable gas soldering iron. The hot exhaust is very good at melting plastic.) A good pair of tweezers is also desirable. One tool which you may find usefully, is a fine spring-hook (Or preferably a set of spring-hooks.) This is simply a dental probe with the end turned over to form a hook, and is very usefully for fitting and removing springs in awkward places. Sets of dental probes can be had for very little money from most electronics tool stockist’s. IMPORTANT: Take your own notes as you disassemble the camera. Wire colours especially may differ between different cameras of the same make and model. Do not force anything that is stiff, or does not appear to be completely free. Usually this means you have missed something. Do not unscrew anything without first examining closely how the parts relate to each other. (It takes ages of trial and error to figure out how they should have been!) ESPECIALLY do not tamper with any screws that are fixed with coloured varnish, or pitch. These are almost always to do with calibrating the camera in some way. If you do not have the know-how and proper equipment it will not be possible to reset these correctly.
The disassembly begins with removing the door latch. Just two screws here. The latch cover has lugs which engage with the front, top, and bottom covers. Removing those is much easier with this removed. Here you can clearly see the lugs on the front and top covers. The parts you can see here are best removed and saved in a safe place, but accessing the spring requires removal of the front cover. At the moment the back cover is keeping the parts secure, so don’t open the back until we remove these parts.
Removing the front cover is fairy straight-forward, but don’t forget the screw lurking underneath the flash hood. Notice the small rectangular transparency with the “P” on it. This normally fits on top of the indicator lamps in the viewfinder. The fact that it is loose leads me to suspect that the camera has been dropped. (In fact it’s a bit lucky that it is still in there, the screen is interchangeable on these, and it would have been little trouble to remove the screen and drop this out. I also have to admit I’ve lost one of these before!) The front cover removed with it’s screws. Make sure that you take note of which screw goes where. They are not all the same.
Bottom Cover Removal
Ok, cover is off. The next task is removing the bottom cover. Again this is a simple matter of removing screws. Also again the screws are different. There are five screws. Once the bottom cover is off, we see further evidence that the camera has been dropped. You can see the door latch spring at the top of the picture.
Now we should remove the door latch components, this is where a spring-hook comes in handy. You can see how it makes the job of manipulating springs much easier, even on this relatively accessible spring. Once spring and latch slide are removed, this interlock arm should also be removed. Now it’s safe to have a good look around the camera.
The large metal plate on the bottom of the camera does not need to be removed. It contains the gear train driving the film advance. In other EOS cameras the film advance is driven by a separate motor built into the film take-up spool. On the left as we see it, there is some tape covering some flexi-board circuitry. This tape has to be removed, and the screws passing through the flexi-board taken out to release it. This is made more difficult by the fact that it has also been glued in place. I have no idea why this was deemed necessary, but the glue effectively clogs the screw heads. You will have to carefully dig out the glue from inside the screw heads before you will be able to remove them. Use a dental probe to do this, and get as much out as you can before attempting to remove the screws, they can be very tight. There are quite a lot of wires that need to be unsoldered before the mirror cage and shutter assembly can be removed. The following pictures record the locations of the various wires so that they can be replaced correctly. Take care that you check the colours of your own camera can be recognised from the pictures. The colours displayed often appear different from the actual wires, and may cause confusion. The preceding images show the wires on the battery side of the lens mount. All of these wires need to be disconnected.
This PCB and the wires can be left in place, it is the voltage inverter for the built in flash. BEWARE HIGH VOLTAGES ON THIS BOARD. There are components on this board which can store a high voltage charge for quite some time, even without the battery. While it is probably not enough to kill a healthy person, receiving a shock is quite an unpleasant experience.
Removing the Top Cover
Before removing the top cover, I find it convenient to remove one or two parts and do some unsoldering. There is no real physical reason for this except that I like to avoid balancing the camera on the exposed circuitry under the top cover while working on the top and sides. First locate the battery switch on the bottom. It’s right next to the flash circuit board so check the section above before proceeding. Remove the retaining screw, and save the glass-fibre insulator. Once this is done, the flexi-board on the bottom plate should be detached from the plate. (Provided of course that you have successfully removed the screws embedded in the glue!) At the other end, the two blue wires should be unsoldered, and the solder tag next to it should also be unsoldered. The six tabs here should be unsoldered too. We should now remove the top cover. To do this we must first remove the retaining screws. Two of these are behind the eyecup. Another two are partly concealed. One in the battery compartment. Another here. Before lifting the cover, set the selector dial to ‘Lock’. Lift the lid carefully, and… If this looks a bit scary, don’t worry. Just note the position of the selector. (The big round transparent thing on the right.) You will need to make sure of the position when replacing the top. The green board in the middle of the shot will need some of it’s wires unsoldering but not yet. Make sure you make a note of the wire locations on this. WARNING: THIS BOARD CONNECTS TO THE FLASH TUBE, IT MAY BITE!
Preparing to Separate the Film Transport
In order to access the shutter, we need to separate the film transport system, from the rest of the camera containing the shutter, mirror cage, prism, lens standard, and the bulk of the electronic. First we need some room to work in. These tapes on the inside of the cover should be removed. This tangle of wires should not need disturbing, but in case you pull one out, I’ve included a couple of shots. The coil you can see here releases the flash head, so don’t be surprised if it pops open should you tinker with it. Now back to the little green board, you need to unsolder some wires here. You can of course unsolder the lot if you want, but you should at least unsolder upper white and blue wires,the pale blue, the brown, and the one which looks grey in this picture on the right of the board. (The sleeving is transparent.) Take care that none of the tracks short out on this board. There are quite large voltages in play here and there is the risk that should they end up in the wrong place they could cause considerable harm to any digital circuits. Now unscrew the little board. More wires need to be unsoldered before we proceed. What we are trying to achieve is to remove the bare minimum to disconnect the circuitry attached to the PCB from the film transport components. There are five wires in this group, note the black wire, and take special note of the location of the brown wire. Next remove the release button PCB. And then remove the screws holding the frame counter mechanism. There’s a small spring bearing against a nylon spigot that drives the counter under the assembly. Take note of how it is fitted. Unsolder the wires from the battery terminals, and remove the screws from the power PCB. You can then disengage the PCB from the battery terminals with the aid of a soldering iron. Lifting the PCB reveals three tags connecting to the selector which need to be unsoldered. The five next them to it connect to the shutter. There is no need to unsolder these unless the shutter needs complete removal. (In this case it transpired that it did. The impact had dislodged one of the shutter coils so that it no longer releases the curtain.) The photocell assembly should now be freed. There are another three tags needing unsoldered here, near the front of the prism. This should be all that’s required on this side. Now move to the other side, and unhook this tab from the housing. It should now be possible to unwrap the flexi-board from the top of the camera and over the prism. It’s not completely released from the camera body, but we don’t’ want to do that anyway.
Under the flexi-board, the rewind gear housing is revealed. Remove this and the gear underneath. Take not of the location of the spring. We should now be ready to remove the mirror cage and shutter assembly.
Removing Cage and Shutter
Remove the screw at the bottom. Then the two screws at the front. The two lower screws shown below should be the last. The whole mirror, prism, shutter, and a whole bunch of circuitry should now be free. To remove it all, tilt it forward in the body slightly, lift a fraction, and draw it forwards. (If I have missed something, you will spot it now!) The shutter should now be accessible.
Disassemble and Clean the Shutter
To clean the curtains the small silver screw at the bottom left should be removed, and the back plate slid to the left to release it. The offending rubber buffer is now removable. As I mentioned earlier, the shutter works OK without it, but cutting a piece of inner tube to replace it may be advisable. This spacer can be removed to allow the removal of the curtain for cleaning. The other curtain is beneath a second plate spaced by a washer on the locking screw spigot. Clean carefully by gently wiping the blades with a cotton bud dipped in isopropyl alcohol while supporting the blades on a flat surface. Don’t forget to wipe in between the blades. After cleaning, the shutter can be reassembled, and the camera should go back together in the reverse order of disassembly.
Re-assembly should be largely the reverse of disassembly, the only points to note are to check the alignment of the selector dial when replacing the top, and double check the placement of all wires when soldering them back. This should be straight forward. (Provided you have not skimped in taking your own notes.)