posted Sunday, 07 November 2010, 19:50 (+0800), by Martin
I spent several hours on Saturday afternoon, replacing the ribbon cable
to the aperture diaphragm assembly in my Canon 17-85mm IS lens.
As mentioned in an earlier post, my Canon EF-S 17-85mm f4-5.6 IS USM lens has been failing with "Err 99", and some testing indicated the aperture diaphragm assembly in the lens was failing under the following conditions:
I bought a replacement cable on eBay from these guys for approx AUD$12, with free shipping from Hong Kong, as I had decided to try repairing the lens myself.
I'm not going to provide a step-by-step guide to disassembling the 17-85mm lens, as there are already a few such guides that I found useful: There are also some more photos from someone who completely disassembled their 17-85mm lens available here.
By following the above-mentioned guides, I was able to disassemble the lens, and replace the aperture cable. Here's a few photos showing various stages of disassembly.
Once the aperture diaphragm assembly had been removed, close examination of the ribbon cable confirmed that there was a crack in the cable, causing an open circuit. This part of the ribbon cable has a relatively tight fold in it, and the cable rolls up and down near this fold each time the lens is zoomed, thus eventually causing a breakage in the cable.
The broken ribbon cable was carefully de-soldered, and the replacement cable installed.
Re-assembly is the reverse of the disassembly, making sure that the various components are put together in the correct order, without having any leftover parts.
After re-assembling the lens, the zoom and focus rings seemed to operate normally, so the best way to test the lens was to mount it on a camera body and take some shots!
Some further testing indicated the image stability mechanism wasn't working properly, but was jerking abruptly. However, with the IS turned off, the lens functioned as normal.
I suspect the IS isn't working due to another ribbon cable I inadvertently damaged during re-assembly of the lens, as shown below.
Providing the IS is turned off, the lens is now working, so I probably won't bother attempting to replace the damaged ribbon cable to the IS mechanism (and I haven't managed to find a replacement cable online yet).
The lens had been completely unusable, but with a new aperture ribbon cable, it is now useable - albeit without IS. A small piece of black gaffer tape over the IS switch ensures the IS cannot be turned on.
Broken Lens
As mentioned in an earlier post, my Canon EF-S 17-85mm f4-5.6 IS USM lens has been failing with "Err 99", and some testing indicated the aperture diaphragm assembly in the lens was failing under the following conditions:
- zoom was between 17mm and 24mm
- aperture was smaller than f/4
I bought a replacement cable on eBay from these guys for approx AUD$12, with free shipping from Hong Kong, as I had decided to try repairing the lens myself.
new aperture ribbon cable
Disassembly and Cable Replacement
I'm not going to provide a step-by-step guide to disassembling the 17-85mm lens, as there are already a few such guides that I found useful: There are also some more photos from someone who completely disassembled their 17-85mm lens available here.
By following the above-mentioned guides, I was able to disassemble the lens, and replace the aperture cable. Here's a few photos showing various stages of disassembly.
wiper mechanism for the zoom contacts needs to be removed
almost there - the outer barrel contains the focus mechanism,
and the inner barrel contains the aperture diaphragm and the IS mechanism
and the inner barrel contains the aperture diaphragm and the IS mechanism
disassembled, with the aperture diaphragm assembly in the foreground
Once the aperture diaphragm assembly had been removed, close examination of the ribbon cable confirmed that there was a crack in the cable, causing an open circuit. This part of the ribbon cable has a relatively tight fold in it, and the cable rolls up and down near this fold each time the lens is zoomed, thus eventually causing a breakage in the cable.
a small crack is visible in the old ribbon cable to the aperture diaphragm mechanism
The broken ribbon cable was carefully de-soldered, and the replacement cable installed.
new ribbon cable installed on the aperture diaphragm mechanism
Re-assembly is the reverse of the disassembly, making sure that the various components are put together in the correct order, without having any leftover parts.
The Results
After re-assembling the lens, the zoom and focus rings seemed to operate normally, so the best way to test the lens was to mount it on a camera body and take some shots!
testing the focus at maximum aperture at 85mm, focussing on the "P" key
Some further testing indicated the image stability mechanism wasn't working properly, but was jerking abruptly. However, with the IS turned off, the lens functioned as normal.
I suspect the IS isn't working due to another ribbon cable I inadvertently damaged during re-assembly of the lens, as shown below.
damaged ribbon cable to the IS mechanism
Providing the IS is turned off, the lens is now working, so I probably won't bother attempting to replace the damaged ribbon cable to the IS mechanism (and I haven't managed to find a replacement cable online yet).
The lens had been completely unusable, but with a new aperture ribbon cable, it is now useable - albeit without IS. A small piece of black gaffer tape over the IS switch ensures the IS cannot be turned on.
Don't ever to attempt to solder a flex cable, it will melt before your eyes, no matter how small of an iron or how careful you are. I've found a paint, containing metalic nickle, sold by GC, if they are still around. Scrape the flex cable to expose the copper trace, both sides of the crack, paint the area with the nickle paint, worked for me. There also used to be a paint containing silver, haven't seen it in a while. It is used for doing solderless repairs of printed circuit boards. I did this on my Canon GL2 one time, where the circuit cracked.