Thursday, 17 May 2012

Aperture flex-cable replacement

The Canon EF-S 17-85mm 1:4.0-5.6 IS USM is a great walk-around lens for the prosumer photographer. However it has problems with the flex-cable, that controls the aperture iris;
When the lens has been in use for a few years, usually after the warranty has run out, the camera will begin to display 'err 01' or 'err 99' periodically, usually when the lens is zoomed in and the aperture is at a lower value than f/4.

The Situation
I have a Canon EOS 60D and I really like the camera, with it I have a Canon EF-S 17-85mm USM, it is a great combination for most situations, it's not the best lens on the market, but you get a lot for your money.
Lately though, it has begun malfunctioning, especially when I photograph outside in good light.
If you use your camera a lot, you know how I feel about a periodic problem with the camera, if it fails to take a picture at just the wrong time, you might miss a great shot. This means that a camera that malfunctions sometimes, is as useless as one that never works.

Why fix it myself?
So I contact my local Canon-dealer and they tell me, that they can send the camera in for repairs. This will cost about 600 DKR (80€/60£) just to figure out what the problem is, then furthermore 600 DKR for every hour it takes to fix and on top of that the price of parts. I figured that this would cost a minimum of 1600 DKR (210€/160£) and started Googleing for a solution.

What's broken and why?
Small part, big problem
I Googled "Canon 17-85 err 01" and a few things came up, mostly posts about the flex-cable that controls the aperture-iris. Apparently Canon has made a bit of a mistake in their design of the lens, the cable consists of 8 tiny wires inside the flex-cable, 4 wires are thicker than the other 4 and the thin ones fail as zooming the lens bends the cable.
This flex-cable cost as little as £2 on eBay if you are not comfortable with soldering sensitive electronics, you can buy a fully assembled aperture for about £25 on eBay.

How to fix it?
After diagnosing the problem and ordering the part, I needed to find out how to take a camera lens apart, without breaking anything.
I found a video on the subject and after watching it a few times, I felt confident that I could accomplish the deconstruction and reassembly of the lens. 
When trying to repair something as complicated as a camera lens, it is very important to have the proper tools for the job, using a wrong screwdriver will ruin the screw-heads.

Tools for the job
  • Phillips Screwdriver #000
  • A pair of tweezers
  • A soldering iron 
Make sure that the tools are anti-magnetic, as the lens contains sensitive electronics, that may be damaged by magnetic tools.
I have chosen to use two different types of tweezers as the tweezers with a curved tip, is sometimes better for removing and repositioning the screws.
It is also a good idea to have a straight-edge screwdriver, as it is good for prying of connectors and plastic-rollers.

Executing the repair
Taking the lens apart, was done following the aforementioned Youtube video.
My lens had a few differences, among others one of the flex-cables were glued to a piece of plastic, but on the whole, the guide could be followed and I ended up being able to remove the aperture assembly.
Aperture assembly after resoldering
Removing the old, damaged flex-cable was rather difficult as the soldering iron will easily melt the plastic or remove the solder from the inside of the aperture motor magnet.
I actually thought that I had unsoldered the contacts in the magnet, but finished the repair just in case I hadn't broken it. Luckily the aperture worked.
But if you know how to solder, give it a try, if you break the aperture assembly, buy a new one, it is cheaper than getting the lens professionally repaired.

Reassembly was pretty much just the reverse of taking the lens apart, but take care that the lens parts are replaced as they were, some parts can easily be turned 120 or 180 degrees and still be reassembled, but the lens might not zoom or focus.

The broken flex-cable
As the malfunction was not permanent, but only occurred at certain zoom-lengths, I knew that the cable would not be completely severed, but I was surprised to find that there was nothing visible wrong with the cable whatsoever. However when I compared the replacement cable and the OEM, it was clear that the new cable was much thicker, not only in the plastic casing of the cable, but also the wires look thicker.

Testing the camera
For testing the camera, first I wanted to try out the aperture motor, as I feared having broken the motor while unsoldering the flex. I tested out the aperture motor, by putting the camera in 'Av'-mode (aperture priority) and while holding down the DOF-button, running through all possible aperture settings.
I did this at all zoom-lengths and kept an eye on the aperture iris, it moved smoothly from f/4 all the way up to f/32.
Afterwards I tested the aperture motor sensor, by taking pictures at different apertures and different zoom lengths. I didn't get any error messages and therefore I assume that the problem has been fixed.

So in conclusion, a fix that would cost at least £160 and take weeks at a Canon dealer, I spent a total of £2.31 and used 3 hours.
In my opinion, anyone who has basic skills at mechanics and soldering, should be able to accomplish this repair, considering the price of the lens, you really don't have anything to loose.
Hopefully my lens will work perfectly for years to come.