As a Canon 300D owner I recently fell foul to the common problem of a failure of the autofocus system. The lens would rotate fully in either direction but never to a point of focus. I did some searching and discovered that it was a problem with the secondary mirror underneath the main mirror that is used in the auto focus system.
The story continued, when after a bit of examination, I discovered that the sub mirror was jammed up under the main mirror and that was the cause of the auto focus failure. The tiny spring holding the two had become dislodged and yet held the two together. When I removed the spring in order to refit it I found what is commonly known as the “half black problem”. This occurs when the sub mirror isn’t lifted fully by the main mirror when the shutter is released and obscures the sensor.
I managed to refit the spring using a technique I found on the web.
However this was only part of the story. The mirror assembly hinges on a small plastic pin and combined with the spring allows the sub mirror to rotate and move up to join the main mirror during shutter release. This pin had broken.
Whether or not Canon accept this as a problem is not my concern. After 4 years and over 10,000 shots wear and tear was bound to creep in. I suppose Canon would put it down to economic reasons. Firstly they can charge to fix your old camera, or secondly you would feel the time was right to upgrade to a new model, which after investing in lenses, wouldn’t be a Nikon…
The broken pin is fixable by someone with patience and care and the right tools. There are many blog posts and articles detailing the fix and I am not going to repeat them in full but I want to add my experience to the procedure in order to help prevent the situation I now find myself in.
The two main articles I used in my repair were by Jan-Erik Skata and Tobbe Arnesson both of which are fantastic but Tobbe Arnesson’s page shows a more step by step approach, which suited me, as I was a bit wary at first.
I also made reference to the 300D service manual which can be found here.
Using the guide I managed to insert a new ‘pin’ in the shape of a paper clip and complete the repair of the mirror assembly. Before putting the camera back together I was able to confirm that the sub mirror rotated correctly around the pin and draw up under the main mirror.
Tobbe Arnesson’s page mentions the difficulty in getting the flash assembly free of the main chassis and I can confirm that it is difficult and also that the warnings of high voltages are true!
What Michael J Dixon notes, however, is that it is possible to diffuse the current in the large capacitor, thereby making the flash board safe and easier to grip and remove without fear of shock. He suggests using a 5kOhm resistor over the discharge points to remove the charge. I only had a 2k2 Ohm resistor so used that, which also worked. I found the discharge points in the service manual detailed above.
Once the capacitor is discharged, removing the board may be easier but still care needs to be taken of the delicate orange ribbon cable that the board is attached to near the legs of the smaller capacitor.
The orange ribbon bends up and away to inside the chassis and does not tolerate a lot of movement - as I found to my cost.
The above shot shows a tiny tear in the ribbon cable that occurred either when removing or replacing the flash board. The effect of this is that neither the flash, nor the metering system will work. You can still take shots but you have to meter yourself, using a best guess approach and bracketing adjustments - not ideal!!
The tear in the ribbon is tiny, only a couple of mm across but the ribbon is double sided - there are connections running through both top and bottom of the cable, so repair is impossible. Also I doubt it would be very easy to remove the ribbon and replace with another as there are many solder points and connections further around the camera.
So all in all, I’m glad I was able to find such help around the internet community but I’m annoyed with myself that I was unable to complete the repair successfully. Hopefully these notes will aid others in their quest!
Or just hand over your precious camera to Canon service and bite the bullet.
As for me… when does the 450D / XSi hit the shops??
Stumble It!
Hi,
such pin broke in my camera just before a week and I’m going to do this operation too. However I’m full of doubts after I’ve read your blog. Are there any other dangerous points like tearing the orange ribbon cable? What would you do if you had such a problem again?
thanks
Yeah, I’d do it again definitely. I’d already decided to upgrade my camera when the 450D comes out. I probably would have kept the 300D as a spare body. Even now I intended to use it a bit, even though the meter circuit is broken.
But that’s with the hindsight of experience. I would say discharging the capacitor is essential. That’s what caused me the problem - worrying about being electrocuted (!) is what made me not concentrate on the delicate parts. Putting the flash board back into the housing is what tore mine.
If you carefully raise the top section where the flash is and pull it forward over the front of the camera you can remove the whole top section, making it a bit easier to slide the flash board back in.
Just keep an eye on the section that tore on mine…. and don’t rush.
What about fixing the broken ribbon with tape and bridging broken lines with cables? I know, that the topology of ribbon is complex, but you have to find only one contact on left part and one related contact on right part of each broken line. Contact is where the ribbon is soldered to the circuit board. Then you can connect them with a piece of thin cable. Use thin soldering iron or find somebody experienced in soldering.
I had hoped that I might be able to bypass the broken section but the ribbon has connections both sides going in different locations, to both ends of the camera chassis. Its really hard to find where the paths reach circuit boards. Its a nice idea but I think pretty impossible in such a small space inside the camera.
Thanks for checking this out and giving support!
Hi,
operation of my canon 300D was successful! oh, I’m so glad…
Cool! Glad it went well for you! Did any of this stuff help at all?
Yes, of course; we were very careful about that orange ribbon cable thanks to your blog.
i’m curious about that technique you used to refit the submirror spring, can you please contact me on kuna(at)chello(dot)sk, and provide me with the link or your notes please ?
i’m trying to fix this problem too.
thank you very much …
No problem.
The spring is straight at one end and hooked at the other, with the coil in the middle.
With the flash on top of the camera facing away from you and the bottom of the case nearest you, when you look into the body you will see where the spring goes on the right hand side.
Hook the coil of the spring over the plastic pivot on the main mirror with the straight section of the spring facing away from you, which should fit into the tiny little groove on the top of the main mirror.
Lift the mirrors carefully and the hooked section will be hanging free underneath. Use a piece of thread tied into a hoop to lasso the hooked end and gently pull it over the top and drop it into the front section of the main mirror, whilst making sure the straight section stays in the groove.
Hope this helps. This is as good a description as any others I have found. Good luck.
yeah, it works, thanks
I’m intensely angry at myself for breaking the exact same ribbon cable after taking all the precautions i could.
Luckily now that I have caused this accidental damage, my insurance will cover the repair, which it will not do for gradual/wear and tear or manufacturing defects! a blessing in disguise….
Hi,
I’ve now struck this problem too, but what makes it worse is that it wasn’t my camera!
When you refer to the pin, are you meaning the one at the very bottom that holds the main mirror to the casing (looks okay in my case), or is there meant to be another sliding one just above that that connects to the smaller secondary mirror?
Thanks.
The pin I refer to is located on the right hand side of the mirror assembly, when you have the camera facing you with the flash above. You can’t really see the pin, it doesn’t protrude into the mirror area. If you look at the third picture in the post, the one with the labels of the mirror area, the pin is located roughly where the label “Spring fits in here” is pointing. Hope this helps.
I have been useing my 300d with the sub mirror flip up so I could use it in manual focus mode. after about a month the spring came off the main mirror. I used you spring replacement technique and put the spring back on, but when ever I click the shutter the front of the spring comes off and the the coils comes off the pin. and sub mirror is in the way of the sensor. Is these something on the pin that keeps the spring form coming off when the shutter operates.
Somehow i missed the point. Probably lost in translation
Anyway … nice blog to visit.
cheers, Correspond.