Canon 300D sub mirror pin failure – Another Story


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??


42 thoughts on “Canon 300D sub mirror pin failure – Another Story

  1. 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?

  2. 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.

  3. 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.

  4. 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!

  5. 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 …

  6. 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.

  7. 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….

  8. 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?


  9. 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.

  10. 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.

  11. Hi!

    Glad my humble instruction could help you.

    You don’t need to worry about being electrocuted by the capacitor though, even if it’s loaded with 300 V the current is too low to be of any danger. But it might feel a bit. 🙂

    You need to be cautios about electrocuting other parts of the camera though!

    Bummer about the flat cable, never heard of anyone else managing that.

    With best regards,

  12. About 18 months ago I had the same problem. My fist attempt didn’t align the new fabricated pin properly so I had to have a 2nd go. On the 2nd go, I got it right, ripped the cable. I disassembled again to check the problem and the rip got worse. It won’t turn on now.

    A month later I replaced the dead 300D with a 40D but nostalga makes me want to get the old camera working again. RIP 300D.

  13. hi, im not sure how to explain it but do you know if it is possible to fix the lever on the right hand side of the mirror that works with the pin an spring to lift the sub mirror? the end of mine has broken off, if you have any help please email me at abrunton(at)stanjames(dot)com thanks!

  14. I’m really close to having my repaired — pin is working and full assembly shows that everything is functional except one thing — the shutter button! Does someone have a better picture of what it looks like with the lid off so I can see if a piece is missing during disassembly?

  15. I checked my picture archive but I don’t have a shot of the shutter assembly I’m afraid. It might just be the way the top section has been seated back on the main body, maybe you should try taking another look.

  16. Had the pin replacement going well this weekend…. however.
    The epoxy i used to lock the new pin in place setup nicely after being mixed and put in place, then as it began to cure and settle into place, went a little runny. It ran through the hole where teh pin was at into the shutterbox, fused the mirror pin in place and it was all over but the crying.

    Luckily I bought a new XSi about 1wk after the 300D went south a little over a year ago. The bad part is that 14yr old was looking forward to using the 300D as a first stepup from P&S.

    Oh well, no pain… no gain. And I sure would not have paid Canon Svc what they wanted to repair the pin (285 estimate).

    Mu next venture will be to replace a dead shutterbox assembly on a 10D.

  17. Thank you so much for the link to Tobbe Arnesson’s website, I followed the instructions and now have my 300D fully working again on the first attempt!
    I couldn’t workout how to leave a comment on his guestbook but if he reads this thank you very much.

    for a living I repair pc’s and laptops so to me it was too much of a hard job but see what they say about the flash board! that was very difficult indeed.

    Thanks again


  18. Hi Steve:

    Great and very helpful blog. I ran into the same problem with my 300D and I successfully repair the submirror pin thanks to your website. However I ran into another problem after the repairing. For some reason now, the LCD panel wont turn on, so I cannot see the aperture, ISO, speed…etc. When I look into the viewfinder I cannot see this information either. Any idea what could be the problem

    Thank you


  19. Not specifically, no. It could be one of the many connectors that has not been seated properly, some of them are a bit fiddly. I’m afraid you may have to open it up again and check each connector to make sure it is secure.

  20. Again, my 300D failed last week too with the spring going – can’t believe Canon construct this part so delicately (perhaps a ploy for you to stump up $$$ to get it repaired or upgrade?). But mine failed after just 5000 shots. Has anyone had repair quotes? I have read between US$250-$300. Any AUS$ estimates? Nots sure whether I have enough confidence in attempting this repair myself!

  21. Hey Readers!

    In case anyone reading this has this fault… As of January 2010 I’m looking for a cheap 300D, 350D, or 400D that if you don’t fancy trying this repair, I’ll take it off your hands!

    Leave a comment and I’ll get back to you.

    I’ll update here if I find one. Thanks

  22. I’ve got a $100 300D with this problem, so what the hell. Thanks for the warning. I plan to reinforce that weak spot on the ribbon with hot melt glue or packing tape before removing the board. Let everyone know how this works.

  23. I am also having a similar problem, but not exactly the same. When I press the shutter release button, the primary mirror on the front budges by a fraction of a centimetre and then stops. It doesn’t come up the entire way. I checked if the sub-mirror pin was broken by disassembling the 300D, but it wasn’t. So the problem isn’t with the pin. Any suggestions?

  24. Thanks for a great guide. Even with your warning I still managed to shock myself twice from the capacitor OUCH! However, it wasn’t that bad, just enough to make you jump and tingle for a few seconds (even the second time!). I fixed the mirror pin no problem, just as you described, but just like you I tore the ribbon getting the capacitor board back in. However, my metering still works, only the internal flash is disabled. As I use a speedlight anyway, that doesn’t matter at all. Thanks for taking the trouble to make this guide. Brilliant.

  25. Just a note for those of you wishing to discharge flash cap. I went to harbor freight and purchased a 3.99 analog Volt Ohm Meter. Set the VOM to DC volts range to 500 volts. Place the probes on the associated Cap contacts. The reading could be around 300 volts, but be patient here, keep the probes on, watch how the reading bleeds down. Keep adjusting the volt range setting down as the stored charge gradually dissipates. Avoid touching probe tips to your body or any chassis ground potential.

  26. One more thing, if it interests you, the sub mirror on my wife’s 300D failed at 8862 cycles, Canon – shame on you. Will definitely consider selling canon lenses and repaired 300D and possibly going back to Nikon. Sure seems like a lot of money to upgrade to “semi pro” Canon camera in order to get a low cost upgrade on mechanical assembly. Nuts, I wasn’t considering the magnesium case.

  27. Steven, Did you ever find a source for a replacement ribbon/flexible PC board? I was given a broken 300d from a friend and I completely broke the ribbon, not just ripped it, during the pin repair. I thought I could still use the camera in Creative mode but now that I have a CF card for it and I start to take pictures, I’m seeing what you mean about the metering not working. 😦 Thx. -Joe

    1. I’m afraid not Joe, it’s a custom design that wraps around the whole body going to different places. In the end, I bought a broken one of eBay and made a Frankenstein’s monster out of bit from both! Now I have one working camera (which shoots infrared!)

  28. hi there everybody, bought mine only 2-3 months ago as a used one. now have a same problem. Reading everybody’s comments, I am skeptical to performing the operation. I am thinking of having it repaired from a private camera repair shop in vancouver which i think will be cheaper than canon servicing. keeping my fingers crossed.

    1. Hi,
      I broken the flexible PCB too.

      Afterwards I thought about the problem and I think the easiest solution to avoid this is:
      Cut the pins of the big capacitor (after discharging !) and remove it.
      Now you can easily remove the PCB.
      To get more ‘space’ you should also remove the upper button from its place.
      After the repair simply solder the two contacts again.

      I hope you understand what I mean.

    1. I didn’t buy a new pin. The piece of plastic on the housing that snapped I replaced with a paper clip, that is the main reason for this post, to show how that is possible. If you have lost the spring that hooks onto the pin, then I don’t know, I have no idea if Canon still makes parts. There are plenty of this type of camera on eBay sold as ‘broken for spare parts’ though.

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