Canon EOS 450D / Rebel XSi: How to repair the defective autofocus

A DSLR camera is a fine thing. My Canon EOS 450D (also labeled as Canon EOS Rebel XSi) gives me a lot of pleasure even with its standard kit lens Canon EF-S 18-55mm 3.5-5.6 IS.

After three years there has been the first defect now. During a mountain hike the autofocus stopped working.

This article outlines how I solved the problem for about $10. And even if your AF is currently still working, it may be interesting to you how to disassemble a Canon EF-S lens.

» Um die deutsche Version dieses Artikels zu lesen, bitte hier klicken.


Autofocus is dead. What to do?

At first I thought that my camera got too much splash water, but even some days later the autofocus remained dead.

Well, not all dead. If the focus was completely retracted, it was possible to focus exactly one time and then the AF was dead again. This meant that at least the focus motor should still be intact. I suspected the lens to be faulty, because everything was working perfectly when it was switched to manual focus mode.

So I tried a friend’s lens on my cam and behold: the AF was working! Now it was clear that my EF-S 18-55mm lens had to be defect.

I was already out of warranty for 1 year, so I had three options:

  1. Giving the lens to a repair center. Too cost-intensive.
  2. Buying the successor (IS II). Matter of expense: about $200.
  3. Disassemble the defective lens and have a look inside.

Since I had nothing to lose I decided to have a try with option 3. Fortunately, because today I hold the EOS in my hands and it’s working perfectly again with the old lens.

If you have a similar issue, the following may be helpful to you. Everyone with some manual skills should be able to reproduce it since no soldering rework is necessary.


Step 1: Disassembling the lens

It’s surprisingly uncomplicated to unscrew the lens if you are using a fitting miniature crosstip screwdriver (screws are tightened quite strongly).

It’s important to use a screwdriver with the right tip which is size PH00 in this case. Don’t work with the wrong tool, you won’t be happy.

At first you have to loosen the four screws on the backside and swing open the top cover. Carefully detach the flex cables (FPCs) from the white connectors. After that you can take off the controller board together with the top cover.

On the picture on the left the cover of the focus gearbox was also removed. This is not necessary and is not recommended! The whole gearbox unit is taken off as a single piece by removing the two silver screws.


Step 2: Replacing the defective FPC

As I had the lens disassembled so far, I immediately spot the broken flex cable which connects the focus position slider with the controller board. Bingo!

Apparently this is a fatigue failure as the FPC is bent and relaxed with every in- and out-move of the lens (during zooming, not when focusing!). Quite a questionable construction from Canon (keyword “planned obsolescence”).

If it is looking similar in your case, you can proceed as described below.

1a) Removing the broken FPC
On the picture in the middle, you can see the defective flex cable on the left-hand side (it only seems to be flexed sharply, but it is really broken straight through). In the background there is the silver slider which has to be removed now (in the picture on the left, the slider is top right). It is maybe a bit hard to unbolt the two screws of the slider. Afterwards the glued FPC can be removed with help of needle-nose pliers when the lens is fully moved out (i.e. maximum zoom).

1b) Ordering the spare part
Now it’s time to obtain the spare part. I got hold of a Canon spare parts list. Every single part of the lens is descripted there in an exploded view.

Fortunately, the broken FPC for the autofocus can be ordered as a single spare part. The part number is:

FPC Focus

You can obtain the spare part directly from an authorized Canon service partner. You find one through your local Canon website. Navigate to Consumer > Support > Product Repair and choose Digital SLR for the product type.

When you do not essentially want an original Canon spare part, you can get the flex cable quite cheap e.g. from eBay. Especially when ordering in China you may have to consider quite long shipping times.

1c) Mounting the new flex cable
The spare part comes with an adhesive film on its backside and can easily be attached to the right place, which is defined precisely by a rectangular deepening. Just remove the protective foil and patiently place the FPC with tweezers. The lug of the slim part leading upwards is also glued on. Be careful for the tappets of the lens body to lock into the holes of the FPC (possibly it’s necessary to bend the FPC a bit).

Finally the FPC should firmly be pressed down with help of cotton swaps or similar.


Step 3: Reassembling the lens

Now it’s nearly done. The reassembly is naturally done in reversed order:

  1. Screw the slider in place.
  2. Mount the focus gearbox with the two silver screws. Mind the long plastic axis to be locked into the short gear collet because otherwise the focus won’t work at all.
  3. Reattach all FPCs to the controller board. A toothpick maybe helpful doing this. The FPCs may be quite rough-running, they have to be inserted carefully and as far as possible. Insert the board into the lens body. Pay attention to the pictures and be careful not to break anything.
  4. Put the grey plastic ring on top (fits only in one single position) and screw the top cover in place with 4 screws.

Now it’s time for a first operational test. In my case the autofocus worked again straightaway (don’t forget to set the slide switch back to AF if necessary).



For me it was worth the effort. I’ve saved 90€ and my old lens is as good as new again.

I hope this documentation is also useful for some of you out there and I am looking forward to your comments. And please feel free to complain about translation mistakes. This would be a help for me, too.


Further reading

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