fredag 5 juni 2009

How to repair broken sub-mirror on Canon EOS 300D / Rebel

I wrote this back in 2006-07-15 and the guide is also available here, but a lot of people still contact me with miscellaneous tips and tricks. Since I don't have the time to update the original post with these it's better if they can comment directly on the post - hence the blog post. BTW, my camera is still running strong three years later!

I don't know anything about other camera models and to be frank, all I know about this one is written below. If you have a different camera or a different problem, try asking at some forum. This one is pretty good:

Disclaimer: I take no responsibility for what might happen if you follow these steps. Your warranty will be shoot and if you screw up, you're to blame. This is just a documentation of what worked for me.

Inspirational sites: 300D repair adventure and Canon Digital Rebel (300D) Modification. None of these are complete and left much to be solved during the operation.


It's not uncommon that the sub-mirror assembly on Canon EOS 300D / Rebel brakes after everything from 10.000 to 50.000 shots (I got 23.000 out of mine). This is due to a plastic pin snapping (not visible from the outside, even with the lens off the camera). It is possible to send the camera to Canon for repair. The cost is usually something like US $200. Considering what a new camera body costs this is not a cheap option for an old camera. If you're camera is still under warranty Canon should repair it for free since it's a design fault on their part.

How to diagnose the problem

All of your shots look like this (note: in some flash/sync combinations a similar phenomena can occur):

This is due to the sub-mirror blocking the CCD, causing a dark area on the photos. Removing the lens and lifting the mirror carefully by hand, one can note that the sub-mirror wont close into the main mirror. The sub-mirror is used by the auto focus and should fold into the main mirror when it lifts out of the way.

The sub-mirror can be flipped into the main mirror by hand

After doing that you can use the camera but the auto focus wont work (setting the focus manually works fine and the camera works just like normal in manual mode).

Fixing the problem

The camera can by fixed. It's not an easy operation and requires some skills with small screws, patience, even more patience and some good luck. But what do you have to loose, the cameras busted anyway (unless you feel you can live without auto focus, in that case, just glue the mirrors together and live with it).

Here are the tools needed for the job:

Needle, glue, small flat screwdriver, long thin small Phillips screwdriver (not like the one pictured), paper clip, magnet, tweezers (for aligning screws), wire cutter and needle nose pliers (last two items not pictured)

You also need good discipline when it comes to taking the camera apart, placing the screws in an order you can later reverse. Don't forget witch screw goes where, they are of different length and threading. There are close to 30 screws in total.

Let's begin with the disassembly

Note: All left/right-directions are made on the assumption that you hold the camera just like during normal operation, facing away from you. That is, looking at the back of the camera.

1) Start the camera and make the flash unit pop-up. Do not close it again during the disassembly, if you do you wont be able to remove the front cover of the camera (trust me, I found out the hard way).

2) Remove the lens, the viewfinder piece, CF-card, main battery and back-up battery. If you have the shoulder strap mounted remove that too.

3) Turning to the left side of the camera, remove the screws pictured. Note that the top screw is longer than the bottom one.

4) On the back of the camera, carefully pry the screw cover loose with the needle. Then unscrew the screw behind it.

5) Turning to the bottom of the camera, unscrew the three identical screws marked with arrows.

6) Under the lid for the CF-card, locate and unscrew the two identical screws. These are slightly longer.

7) Now, carefully remove the back cover from the rest of the camera. There is a flat cable going from the black and gray information LCD-panel, lift the lock on the connector and take this cable out from the circuit board. The picture shows the connector unlocked. Just lift the black/brown part with a small screwdriver and then pull the cable straight out.

8) On my camera, the silver rim with the "Sony"-marking around the large color LCD came loose and stuck with the back cover of the camera. If this happens for you too, repair that part assembly before you continue. From bottom up it should be the white backlight, a black plastic rim, the LCD itself and lastly the silver rim.

9) Now it's time to remove the front cover. Turn to the right side of the camera and remove the three screws. They're all the same size.

10) Turning to the bottom, remove the four screws. The single one on the front is longer then the three others, who are identical.

11) Now unscrew the two screws on the front right under the flash. These two are slightly longer and identical.

12) Now look inside the battery compartment. Towards the front there are two screws (identical). These little buggers took me some time to locate. With a long thin phillips screwdriver inserted from the back you can unscrew these. My screwdriver was a little to thick but some mild bending got it where it needed to be.

13) Now slide the hinge on the battery hatch away and lift the hatch off. Cool feature! :)

14) Unscrew the hinge base. Note that there is a difference between the left and right side (different spacing between the holes and edges) so pay attention when reassembling this one (you can't go wrong). The screws are identical.

15) Now all screws holding the front cover are removed. With gentle force, lift the bottom away from the tripod mounting hole and lift the front cover off the camera. No cables are attached between the cover and the rest of the camera. Thankfully!

16) Okay, that was the easy part. Now let's move the top cover a bit from the camera. This ones attached with quite a few wires and flat cables but no soldering required! Start with removing the two flat cables from the top left corner, looking at the back of the camera. Just lift the brown hinges and pull the cables out. Make sure both of these come back to the outside when putting the camera back together. One of them escaped inside the top cover for me costing me some additional fiddling.

17) Remove the long screw on the top right.

18) Remove the two (identical) screws next to the view finder and the dioptri screw too (unscrews just like a normal screw).

19) Locate the black tape on the right front side of the camera and pull it loose at the top. You can leave it stuck on the bottom if you want. This is just to give the wires more room to move around as we lift the top cover off the camera.

20) Carefully dislodge the top cover straight up. You cant remove it fully but you can move it a few mm upwards. Then unscrew the two identical mini-screws holding the shoulder strap mount on the left side and then remove the shoulder strap mount.

21) Find the two identical screws that hold the circuit board on the front of the left side of the camera. One is quite obvious (not pictured) and the other is hiding a bit. Also note that there are two pins, one next to each screw. These help holding the circuit board in place but when moving the circuit board you need to work with them.

22) Now you need to move the circuit board away from the camera. Moving it towards the top and at the same time moving the top cover away is the way to go. Be really careful here, the big capacitor holds something like 220 volts (measured) even though the batteries have been away from the camera for quite some time. Try not to short-circuit anything with that voltage! You might loose a circuit board here so pay attention to what you are doing. To make matters worse it's a really hard task to move the circuit board out of the way. On the picture below I have marked the three main problem areas. Moving the circuit board into this location is the best way to move it out of the way. I almost went mad during this step.

23) Congratulations! You have now successfully located the problem zone and can actually start the repair of your camera! The culprit sits where the green arrow indicates.

24) Taking a closer look, this is what you find. This is the pin. There is no obvious way to remove the broken pin from the mirror housing.

25) With the needle, trace the ring around the pin. This loosens up the glue that attaches the pin to the mirror housing. After that, carefully pry the pin away from the mirror housing using a small flat head screwdriver. Someone actually managed to come this far only to drive the screwdriver into the mirror housing totally wrecking the camera. Learn from him/her.

26) After some careful bending, the pin gets loose from the mirror housing. Note that the glue is quite gooey and not of the hard kind.

27) Here you can see the broken "pin". The actual pin has broken away from the base and is nowhere to be found. When Canon repairs the camera they replace this part with a metal one. Let's do the same, shall we?

28) Straighten a normal metal office paper clip and insert it into the hole in the mirror housing. Let the mirror be in it's normal down position. Hold the pin and try flipping the mirror up and down with your finger. Note that the sub-mirror now moves with the main mirror. That's the ticket. When you find a optimal amount of paper clip penetration, take a marker pen and draw on the paper clip. This way you know how long the protruding pin needs to be.

29) Now start bending the clip into something with a base and a protruding pin, there is no need to worry about clearance towards the circuit board - lot's of space there. When you feel satisfied, cut the clip down and try it in the camera. The mirrors should move around freely and the sub-mirror fold into and out of the main mirror.

30) Place the new pin into the mirror housing and put a drop of some thick glue onto it (I used Epoxy resin, a glue gun might work too). Make sure the clip does not float in the glue, it should be flat to the mirror housing. Just like when you confirmed it's operation. If you use a loose/running glue it might find it's way down to the mirrors, not good.

31) Check that the mirrors are moving so that you did not make the clip to long or short and that no glue found it's way to the mirror hinges. I got lucky! :) When all seems to be working, it's time to reassemble the camera. Just start scrolling back on this page step by step. When remounting the back cover, make sure the sensor for the CF-card bay door is free to move. Not focused picture below. After the full assembly the camera should work just like normal again. It worked first try for me but you might need to go back and re-seat some of the flat cables.

49 kommentarer:

Tobbe Arnesson sa...

One reader suggested: "I would like to suggest one note for step 22 (the tricky-fiddly bit) and that is if you remove the metal lens mount ring (by the 4 identical screws on the front) you can get the little metal tab (the lens release button) out of your way, making it a hair easier to move the circuit board out. There is a little spring under the tab that I had to be a little careful with, and I also had to be careful to remember the orientation of the thin metal spring-discs under the lens mount, but it was well worth removing to help get the circuit board out."

Tobbe Arnesson sa...

Another reader has a tip for not loosing the parts: "I made a flimsy sketch of the apparatus and stuck the screws on it using double-sided tape. No screws and tiny parts lost!"

Tobbe Arnesson sa...

Yet another reader ran into this little problem: "My only issue with the repair was after I put it all back together again, the camera was acting a bit strange. The small LCD didn't work properly in a strange way: If there was no CF card in the camera, it looked almost normal, except the ISO selection wouldn't show up. If there was a card in the camera, the LCD would only show "EOS" while booting, then nothing, unless I activated the menu system, in which case the battery indicator showed up. None of the normal displays were visible.

I ultimately discovered, that the ribbon cable connecting the back of the camera has to be pushed in a bit further than I had apparently done, so
after taking it apart and putting it back together again a few times, it was finally back to normal. Phew. :)"

Tobbe Arnesson sa...

A tip for how to easier remove the flash-board if you're into soldering: "I have managed to folow the instructions until the last two screws wich hold the shoulder strap .These were impossible to unscrew , so I 've cut the legs of the big capacitor , extract easily the little board , make the hinge operation, than solder the capacitor legs back. First I have discharged the capacitor through a 500 ohm resistor which made a "plich " sound and give a little smoke . In the end AF works but I have no flash . Maybe I've killed the big capacitor , maybe my solders weren't so good (I was using a soldering iron with no temperature control...crappy tool :( ). It's ok though, I have rarely used the flash , and the possibility for mounting a external one still exists."

Two days later this came in: "It's working again , it was only a bad solder."

Tobbe Arnesson sa...

And here's a reminder to be careful around the big capacitor: "The capacitor was a story of it's own, I wanted to measure the voltage (and I know what to do, worked with 500Amp power supplies in use) and managed to short circuit it by accident, no big issue, the burned of chrome on the tip of my multimeter will always remember me of this task =)"

Tobbe Arnesson sa...

And apart from these I've got close to a hundred e-mails with success storys. :D Only one person seems to have ruined the flash circuit board but never used the internal flash in the first place.

Tobbe Arnesson sa...

Yet another mail: "Hello,

First let me thank you for your excellent “how to” for the fix of the sub mirror. Your explanation and close up shots were very helpful.

I have put the camera back together and I get an error 99 when I try to take a shot where I need the flash, it says busy then I get the error 99.

Also I can not get the flash to pop up by pressing the flash button. It does pop up no problem in automatic, but I cant shoot with it.

Any help?

I think I did everything quite well, although I may be possible the circuitry to the flash was damaged when I moved the circuit board out, although I didn’t notice anything, (I did note there was a circuit near the flash button that was getting in the way.)


I suggested go back and make sure all the flat cables were attached correctly and got this reply:

"I just took it apart and reseated the flash button cable which was tucked completely in the wrong spot."

But he lost a screw in the process and has not made sure it works, but I'd say it does. :)

Tobbe Arnesson sa...

Received another couple of e-mails with success storys. One managed to stun himself on the capacitor - beware! :D

The other noted this: "I might add a couple of things to your directions, if that's not presumptious. Something I did that really helped keep the screws and pieces in order was to take a sheet of paper, write out the step number, and have a piece of tape (rolled so it was sticky side out) next to that number. When I took out the screws, I stuck them to the tape. I could even place them in whatever order made sense to me. Having them on the tape kept them from getting bumped around (which would have happened), and when I reversed the order, there everything was.

I also noticed something in step 12 where the screws in the battery compartment were just out of a straight shot of the screwdriver (you said you had to bend things a little). There's a piece of flat plastic blocking the way, where the screwdriver would fit. This piece is easily removed with one screw and a slideout, and once removed, there are two holes right where the screwdriver can go to reach the screws. My problem was the shaft of my screwdriver was too short, and I still had a booger of a time. "

Dennis sa...

now my camera works again!jippie!
i did stun myself on the capacitator! quite unpleasant.. :)
i have a tip for you guys who havn't done it.
you don't have to bend the screwdriver on part 12, (i accidentally broke the cf hatch senor while trying this... )
all you have to do is unscrew the screw under the cf bay on picture 9 and remove the plastic there, then two holes for the screwdriver appears and it become super easy to unscrew the screws for the front cover!!!

thank you for your guide,

Kind regards,

Karel sa...

Thank you for you SUPER manual.Now 300D work fine.Im lucky :)

Rene sa...

Worked like a charm... You forgot one small step. After you remove the first couple screws you have to remove the black plastic cover on the left side. I figured it out pretty quick, but It did make me second guess myself.

Peter sa...

Thanks, Cam is back again :D.

Argh, cant comment here with IMG Tag.
I made a Blog-Entry as a comment for this acticle:

Lots of useful additional hints there:

ps: in english afer the ======== line

Tobbe Arnesson sa...

Peter, glad too hear another success story! Here's your link click-able, great additions!

Jeffer sa...

THANK YOU!!! Fixed mine yesterday. :)

Thomas Krause sa...

Hey Tobbe,

great guide - thank you very much! As mentioned before this link gives some very good additional tips:

As you wrote the biggest issue was the big capacitor (disassembly and assembly) - that was really, really tricky.
But for me the voltage was no problem, because I've disassembled the capacitor a day after the rest...

greetings from Germany

Ronald sa...

Hi everyone,

First off, a very big thanks to Tobbe and all supporters! I did it als, but sadly I have managed to break the cable of the circuit board in step 22. Now my flash doesn't work, I get error when I want to shoot in auto mode when the flash pops up but doesn't work, of course. Is there anything I can do? I am very new in this. Thanks and graatings from Holland!


Anonym sa...

Be *very* careful on step 22! I had the same problem as Ronald, and I broke the cable to the flash circuit board. Maybe those circuit cables have become brittle over the years?

Anyway, camera back together and it works fine except for when it tries to auto-flash. All the Creative modes work fine and if you attach an external flash the program modes will work fine, too.

Now to find a donor Rebel to get a replacement circuit board from...



Anonym sa...

Thanks for the great info! Success all the way around. For anyone discharging the cap, you may wish to use an analog meter placing the probes on the associated cap contacts in DC volts mode. The resistance is high to enough safely complete discharge operation.

Thanks again, The$torm

Kai sa...
Den här kommentaren har tagits bort av skribenten.
Anonym sa...

thanks for the tutorial.

It worked like a charm and only took about 5,5h.

...But the shocks I got were really intense. ;-)

Tobbe Arnesson sa...

Glad it worked!

I suspect the switch pictured in step 31 was the reason the camera would not start when you first tested it.

Anonym sa...

Greetings from London! My Canon 300D sub-mirror broke while on holiday last year - I found your site and followed the instructions and... MAGIC! It's fixed! Thank you so much for going to all the effort of posting your step-by-step guide, it was all so easy to follow! I used a paperclip for the new pin, it's as good as new!

I didn't need to remove the shoulder strap mount in Step 20.

I also got 2 electric shocks from the capacitor in Step 22!



Anonym sa...

any advice for removing a stripped screw head?

Tobbe Arnesson sa...

Ask Google that exact question and you'll get tons of advice. Best of luck!

Greg sa...


Thanks for your very thorough instructions on the repair of the EOS 300D autofocus. I just completed the repairs on mine. I used some slow setting, JB Weld epoxy, so I'm waiting until tomorrow, to test the autofocus, but the little mirror works as it should, with no hangups. I'm almost surprised that the camera powers up, though, considering how many times I shocked myself with that dumb capacitor.

orly_andico sa...

Ok I know I shouldn't be wasting my time with the 300D, but I found one really cheap with the sub-mirror problem and I've always wanted to remove the hot mirror but didn't dare do so on my more modern camera..

So the 300D had the broken spring, but was otherwise working fine. I followed the instructions here and put in the paper clip bit.

However I decided to go further and replace the hot mirror. Unfortunately I broke the piece of glass from Edmund Optics while trying to scribe/cut it (and I'd purposely broken the hot mirror because I couldn't get it out of the plastic frame).

So I decided to have "naked" camera - no hot mirror replacement. It won't focus anymore (so the whole sub-mirror repair is pointless) but I was planning to use it for astrophotography anyway (and telescopes have lots of focus travel).

Now the problem.. after putting it all together, I get Error 99 every $%#$ time I trip the shutter. When I put it in bulb mode I see that the shutter never opens. The mirror just flips up, then flips down immediately.

I'm pretty darn sure I didn't screw around with any shutter connections..

orly_andico sa...

And.. I'm pretty sure I put the ribbon cables back correctly, because metering works, AF works (!) flash works..

It's just that taking a picture doesn't work.

leduc sa...

Thank you very much for this manual, it works!!

step 22 is very difficult...i managed to disassemble the thing after a while..and only with a little electric shock. i thougt that was it...

i didnt manage to reassemble the thing in step 22 but after i cut off le small plastic pin (left one) which holds the circuit board in place, i finally got there by levering the circuit board on the forer plastic pin with a screw driver.

while reassembling, i got another electric shock, this time quite painful. and finally a third one with a flash..i was really astonished, that the camera works perfectly anyhow!

Anonym sa...

Thank you for this Perfect Tutorial. Fixed mine successfully.

Ricardo sa...

Fantastico! Ho appena finito di riparare la mia 300D! Per scaricare il condensatore (almeno parzialmente) ho scattato una foto con il flash e immediatamente ho aperto lo sportello della batteria: in questo modo anziché 300V mi sono trovato con una carica di soli 113V, molto più rapida da dissipare.
Grazie di cuore della preziosissima guida!

Danijela sa...

I just want to thank you for the brilliant set of instructions.
I got my hubby's old EOS 300D after he got himself a new 50D ... and it died on me after just 150 shots. Thanks to you I'm back in action.
Instructions were very easy to follow and for once i had all the right tools. I actually printed the instructions and than taped the tiny screws next to relevant pictures so I would have some clue as to where things go. (I am very good at dismantling things but not at putting them back together) Step 22 was quite easy as I used small pliers rather than fingers to get the circuit board out, or maybe i was just lucky. My hubby did assist a bit and gave me a lot of moral support but I basically did the job myself and I am immensely proud right now
In any case, thank you again.

Anonym sa...

thanks for instructions!

i shocked myself with the capacitor (didn't have anything handy to discharge it) now because of it (or cables?) the Flash does not work, and the 5 red focus point lights don't light up. otherwise camera works, and autofocus works (i just can't tell which point got focused on)

because it works, i don't want to chance it and take it apart again just to reseat the ribbon cables.

anyone else got the red lights not to light up?

Anonym sa...

It seems to work but alas! Some tiny spring came out somewhere around the mirror and I have no idea how to put back this very nasty piece. Can someone maybe help?

Ricardo sa...

Volevo segnalare un problema e la sua risoluzione. Attenzione al nuovo perno in metallo: essendo lucido può generare dei riflessi che sulla fotografia appaiono come puntini rossi (si vedono ingrandendo molto la foto), normalmente sono in basso a circa 1/3 della foto partendo da sx. La soluzione è semplice: basta colorare con un pennarello nero (possibilmente opaco) il perno prima di montarlo (io l'ho fatto dopo sollevando lo specchio).

Anonym sa...

Thank you so much for your tutorial. I fixed this problem easily. But I generated another problem. At step 22, I tore a little flex circuit, and now my canon doen't work. So beware of it when you fight with the board at step 22.

Gábor és Andi sa...

Thank you very much for the precise description! My camear has been repaired according to this and it was successful! :)

Anonym sa...

put camera back together and turned it on
all i get is red flashing light in the viewfinder
any suggestions?

Danza Kuduro sa...

A PERFECT Manual. Without it the (dis)assembly would have been a neverending story. Thanks very much for your efforts!!

To really really tighten the pin (which is the metal office paper clip as described in 28) I took a soldering iron and melted it into the plastic. Then I took a glue-gun to assure it's really really tight ;-)

Beware: you must work precisely as a pin fixed like that can't be moved again (eg if the pin ended up too long).

So thanks again! Camera works like a charm now :-))

Anonym sa...

Another happy customer!
My main concerns were the capacitor, ripping a ribbon cable and mashing a tight screw head :

Capacitor discharged with resistor & voltage checked with a meter.

Didn't rip a cable (phew!) but watch out for the skinny one attached to capacitor board (step 22).

Nearly mashed up the two screw heads in step 20. I was using rubbish screwdrivers that were too soft. Switched to some better drivers and all was ok.

Used the top tip of sticking all the various screws to paper and labeling them with the step number.

This step-by-step guide is the best although other websites give some useful additional info eg:

Chuck E. sa...

Thank you for taking the time to write this up. Saved me so much time. I took me about 2 hrs going slow. Found my Rebel at a thrift store "AS IS" for $20 USD. I was using it manually for a while and was so impressed with the photos I had to fix it. Works like a charm.

EGR Blogger sa...

Thank you for the excellent instructions! This saved my camera....I read a lot of the comments and followed a few suggestions that made the job less stressful:

1. Used the back side of tape to organize screws for reassembly

2. Used an analog voltmeter to discharge the flash capacitor (300D service manual shows discharge points - this can be found on the web)

3. helped avoid breaking the ribbon cable going to the flash circuit board by disconnecting the cable near the view finder (one screw holding a clamp) and lifting off the cable at the flash button (glue underneath)

4. for step 12, removed the black plastic cover (one screw that can be seen in step 9 (exposes access holes)

5. When reassembling screws where I couldn't hold them, I used glue stick on the end of the screw driver.

Once again, your instructions and photos are fantastic! Thank you!

Marcin Adamski sa...

Just wanted to say thank you. Saved my Rebel. With your instructions the whole procedure was a breeze.

Nikola sa...

Great procedure and help. Thank you.Saved my Canon 300D :-)
Best regards,

Anonym sa...

Awesome job with this tutorial! It is a few years old, but always comming back! :)
I have managed to rescue my 300d, but uppon reassembly I now have a faulty jog wheel! It wont turn left or right. I have quadrupled-checked all the ribbon cabbles, but does anyone have the ideia of witch could be broken or merely loose?

Best Regards to all

Ricardo Camarinho

Posi sa...

While probably not the most elegant solution to fix the issue, I attacked from the other end. I used the paperclip from inside the lens area to push through where the pin normally would be, then I cut a bit of paper clip off the right length and stuck it in the hole with a very tiny bit of super glue gel on the tip. It took all of 3 minutes, and my Rebel is auto focusing again like a champ. I'll have to keep an eye on the pin, to make sure it doesn't wander, but it looks good so far.

Andreas Janke sa...

Hi, thank you for your excellent work so much! I did it today, without the slightest problem! Some remarks:
- double sided adhesive is very useful. I numbered it, and wrote the numbers on your script; so identifying those screws was easy.
- Inserting the flat cables is tricky. I used the paper clip, it fits in the small holes of the cables. Then it was no problem to push gently into the plug.
- I popped up the flash a week ago and removed the batteries. Therefore, I was pretty sure NOT to get electrocuted - but was careful anyway.

My EOS 300 D will now work for, say, another 30.000 pics :-)

best greetings from Kiel, GE

Anonym sa...


in order to replace the screws removed in the right place, I usually print a picture of the device, and I scotchtape each screws on the picture.

When assembling the device, just peek the screw from the picture to the device.


Anonym sa...

Thank you so much for your "walkthrough " it was so funny to actually fix something and to bring live to the "old lady" again.


Jake sa...

I failed on removing the flash circuit board. There is a thin ribbon branching from a larger ribbon that goes to this and there's very little play in it; it began to tear off. Also, if you're not careful, the top cover will come off completely, ripping a couple of wires off the main board.

Anyway, on reassembly I now have a differently semi-working camera; it can now auto-focus, but has no flash, comes up with Err 99 after each photo and has to be switched off and back on again before taking another [and won't take 'rapid-fire' pics], and I'm not sure it can transfer them to the computer, though that was always an issue (computer says 'device driver software loading').

I since wondered if a drawing pin might work better as a replacement part than a bent paper clip, or as Posi suggested working from inside the lens area.