The challenge is trying to get to this single screw, which involves the separation of the lens into over 10 components, and the removal of about 20 small screws. Hopefully this guide will make the disassembly job a whole lot easier.

First, a reminder of what the lens looks like.

Turn the lens on its side with the connection contacts closest to you. There are 2 tiny Philips screws to remove.

Balance the lens on its front with the metal lens screw lock ring visible. There are 4 small Philips screws to remove.

The metal ring can now be hinged apart. This next step is the most difficult. The inner black plastic ring is connected to the metal outer ring with 4 plastic clips in the inside. By pushing the clips towards the center, the black plastic ring can be removed from the top of the metal outer ring. Much care is needed due to the ribbon cable still being attached to the connection contacts allowing for a gap of roughly no more than 1cm.

Once the inner black plastic ring is removed, the outer metal screw lock ring can be removed, exposing the PCB protected by a black plastic housing.

Disconnect a single pressure ribbon cable attached to the inside of the black plastic housing which will then allow for its removal exposing the PCB.

Disconnect the 5 ribbon cables from the PCB. 2 are pressure connected, 2 with a hinged clip and 1 with a pressure clip. Unscrew a single Philips screw allowing the removal of the PCB.

Remove the 5 screws (circled in red) holding the outer black plastic ring allowing the remove of the black plastic ring. Then remove the 3 inner screws (circled in blue).

Turn the lens over and remove the rubber zoom grip. It can be removed by inserting a very thin screw driver under the rubber and working your way around.

With the rubber zoom grip removed, rotate the lens until you find a black rectangle sticker, peal this off to expose some contactors.

With a Philip driver, unscrew the contactors. I actually performed this when reassembling the lens and slightly damaged them. It is better to remove them at the start to prevent this.

There are 3 screws sitting on small metal tubes between a groove, finally remove these.

With these removed the inner lens portion can now be removed from the outer casing.

You now have access to the problem screw(s) that need tightening. Once tightened, add some Loctite or nail-polish to stop the screws becoming loose again.

Some do’s and don’ts

• don’t remove the front lens sticker or 3 screws behind it.
• don’t remove the zoom sticker with m/ft increments.
• don’t touch or disassemble any of the focusing ring!
• do keep your UV filter on the lens, you can still remove the rubber grip with it on.
• do make sure the focusing pin between the inner and outer len is in place.

References

• FixYa post by Gert Jan [fixa.com]
• Canon EF 20-35mm f/3.5-4.5 USM Lens Repair [photo.net]