The first disassembling of an unknown lens normally takes a lot of time for me – and sometimes I make unnecessary steps.
If You want only to change the aperture module, or only the aperture flat cable, You can do it in the following way (the first steps are not on the pictures, so the USM module and the electronic board are already dismantled.)
If You want to clean the internal side of the lens, You have to disassemle the lens completely, of course.
These are the 3 guiding rollers (in fact, there are 3 x 3 rollers, positioned at 120 degrees).
No. 1. is for the last lens group,
No. 2. is for the IS module moving lens,
No. 3. is for the aperture module.
At first, You have to get out the No. 1. and 2. (3 + 3 rollers and 3 + 3 screws). At the first time is not very easy, because they sit very tight in their place.
You can help this with a small flat screwdriver, or with a big wood-screw, using it like a cork-screw. The best is, if You make a small tool for this operation, like this:
See here: https://canonrepair.wordpress.com/2013/03/16/lens-disassembling-tools-roller-extractor-clamp/
The rollers are apperently the same size, but is good to keep them separately for each group.
Now You can pull out the last lens TOGETHER with the IS module (because the IS is in the inside of the lens module).
Don’t forget , You will have to put it back in this position. It’s easy because the two flat cables give you only one possibility.
The next step: to take out the 3 rollers No. 3 (for the aperture module.)
You may take out the screw for the flat cable only now.
After that, you can pull out the aperture module, with the cable, and the long black metallic guide.
Be careful, the new aperture comes without the metallic guide, so you have to use the original!
Assembling in reversed order 🙂
For greasing the guides, rollers I used a PTFE + silicone oil based grease – (in fact a grease for Volvo cars), but be carefull, only the really needed amunt, otherwise You will have grease on the lens.
By the last lens which I’ve repaired I tried to change only the cable. The operation was successfull, soldering OK – but the lens was not working. No contact problems, and nothing wrong measurable.
After complete change of the aperture, was good.