Canon 99 error or how to disassemble Canon 17-85 IS USM and replace diaphragm unit

Few month ago my Canon 17-85 lens started giving «Error 99» with my Canon 400D DSLR camera. Little googling, and I found the cause of this. Problem was in the diaphragm unit in the lens. Diaphragm unit connected to the lens motherboard with flatcable, which is damaged with time, when you use zoom ring. The only way out is to replace flatcable or diaphragm unit with flatcable assembly. Because now I live in Thailand, and I don’t have a copper, I ordered diaphragm unit assembly on EBay.

This is my lens. Beauty :)

Canon 99 error, disassembly canon 17-85 IS USM, change diaphragm unit

We need some tools to disassembly the lens:

  • Good Phillips screwdrivers PH.0 and PH.00 sizes.
  • Tool to disassembly plastic housings.
  • Latex gloves.
  • Small boxes for screws. There are a lot of screws of different sizes in the lens. Very convenient to place screws of different types in different boxes.
  • Plastic film or something like this to cover inner lenses, when you get it out.

This is not a official Canon guide. All responsibility is on you. Remember: after disassembling the device, you lose your warranty!

Let’s repairing begin.

Take the lens.

Canon 99 error, disassembly canon 17-85 IS USM, change diaphragm unit

Turn it to see lens mount and unscrew 4 screws, marked red.

Canon 99 error, disassembly canon 17-85 IS USM, change diaphragm unit

Turn lens again and unscrew 2 screws from side.

Canon 99 error, disassembly canon 17-85 IS USM, change diaphragm unit

Lift lens mount a little bit. Attention! Lens mount is connected to the motherboard with flatcable. If you will lift lens mount too much, you can damage flatcable. On this step you need to remove plastic  ring in lens mount. Plastic ring attached to aluminium lens mount with 4 latches.

Canon 99 error, disassembly canon 17-85 IS USM, change diaphragm unit

Carefully use something thin and long, like screwdriver to press to each latch. You need to press on the latch towards the central and up at the same time.

Canon 99 error, disassembly canon 17-85 IS USM, change diaphragm unit

When you open all 4 latches, plastic ring can be removed.

Canon 99 error, disassembly canon 17-85 IS USM, change diaphragm unit

Remove plastic ring.

Canon 99 error, disassembly canon 17-85 IS USM, change diaphragm unit

Remove aluminium lens mount.

Canon 99 error, disassembly canon 17-85 IS USM, change diaphragm unit

Now we can see lens motherboard.

Canon 99 error, disassembly canon 17-85 IS USM, change diaphragm unit

Turn lens and remove rubber zoom-ring.

Canon 99 error, disassembly canon 17-85 IS USM, change diaphragm unit

Rubber zoom-ring is removed.

Canon 99 error, disassembly canon 17-85 IS USM, change diaphragm unit

Unscrew 3 screws under zoom-ring.

Canon 99 error, disassembly canon 17-85 IS USM, change diaphragm unit

Remove plastic protector.

Canon 99 error, disassembly canon 17-85 IS USM, change diaphragm unit

Unscrew the screw that holds the metal brush. Be very careful with brush contacts, it’s easy to damage it.

Canon 99 error, disassembly canon 17-85 IS USM, change diaphragm unit

Turn lens and remove plastic ring with text using small screwdriver. There is a special hole in the plastic ring for this operation.

Canon 99 error, disassembly canon 17-85 IS USM, change diaphragm unit

Unscrew 3 screws under plastic ring. Attention! There are only this 3 screws are adjustment screws. Before unscrew it, you need to mark it positions on the front lens.

Canon 99 error, disassembly canon 17-85 IS USM, change diaphragm unit

Remove front lens.

Canon 99 error, disassembly canon 17-85 IS USM, change diaphragm unit

Unscrew another 3 screws under front lens.

Canon 99 error, disassembly canon 17-85 IS USM, change diaphragm unit

Done.

Canon 99 error, disassembly canon 17-85 IS USM, change diaphragm unit

Remove plastic ring.

Canon 99 error, disassembly canon 17-85 IS USM, change diaphragm unit

Plastic ring is removed.

Canon 99 error, disassembly canon 17-85 IS USM, change diaphragm unit

Now you can remove telescopic zoom-tube.

Canon 99 error, disassembly canon 17-85 IS USM, change diaphragm unit

OK. Now turn lens and remove lens housing. There is a flatcable connects housing with motherboard.

Canon 99 error, disassembly canon 17-85 IS USM, change diaphragm unit

You need to disconnect this connector to release housing.

Canon 99 error, disassembly canon 17-85 IS USM, change diaphragm unit

Housing is removed.

Canon 99 error, disassembly canon 17-85 IS USM, change diaphragm unit

Remove focus ring by pulling it away.

Canon 99 error, disassembly canon 17-85 IS USM, change diaphragm unit

Focus ring is removed.

Canon 99 error, disassembly canon 17-85 IS USM, change diaphragm unit

Now we need to remove motherboard. First of all unscrew 1 screw. After that take out all flatcables from connectors. Upper flatcables is removed by pulling it away from connector. In big connector, from the bottom, you need pull black part of connector, under the cable, and than take out flatcable. In other connectors you need to remove dark gray plastic clips, by sliding it away, and after that take out flatcable.

Canon 99 error, disassembly canon 17-85 IS USM, change diaphragm unit

We have removed the motherboard.

Canon 99 error, disassembly canon 17-85 IS USM, change diaphragm unit

And backside of the motherboard.

Canon 99 error, disassembly canon 17-85 IS USM, change diaphragm unit

Continue. Unscrew 3 screws, and remove the lens.

Canon 99 error, disassembly canon 17-85 IS USM, change diaphragm unit

Lens is removed.

Canon 99 error, disassembly canon 17-85 IS USM, change diaphragm unit

Unscrew 5 screws. Actually, 6 screws must be here. But my lens has only 5.

Canon 99 error, disassembly canon 17-85 IS USM, change diaphragm unit

Remove plastic ring.

Canon 99 error, disassembly canon 17-85 IS USM, change diaphragm unit

Unscrew 3 screws. Actually, 6 screws must be here.  :)

Canon 99 error, disassembly canon 17-85 IS USM, change diaphragm unit

Remove zoom tube from focusing motor.

Canon 99 error, disassembly canon 17-85 IS USM, change diaphragm unit

Two big parts :)

Canon 99 error, disassembly canon 17-85 IS USM, change diaphragm unit

Get the zoom tube.

Canon 99 error, disassembly canon 17-85 IS USM, change diaphragm unit

Unscrew 3 screws and remove front focusing element.

Canon 99 error, disassembly canon 17-85 IS USM, change diaphragm unit

Front focusing element.

Canon 99 error, disassembly canon 17-85 IS USM, change diaphragm unit

Unscrew 9 screws.

Canon 99 error, disassembly canon 17-85 IS USM, change diaphragm unit

Remove plastic sliders. I used larger size screw for this :)

Canon 99 error, disassembly canon 17-85 IS USM, change diaphragm unit

Screw larger size screw in the slider and then pull it out.

Canon 99 error, disassembly canon 17-85 IS USM, change diaphragm unit

When all 9 sliders removed, you can release image stabilizer module and lens.

Canon 99 error, disassembly canon 17-85 IS USM, change diaphragm unit

Diaphragm unit is still in the tube. Unscrew 1 screw and release flatcable to remove diaphragm unit.

Canon 99 error, disassembly canon 17-85 IS USM, change diaphragm unit

The diaphragm unit.

Canon 99 error, disassembly canon 17-85 IS USM, change diaphragm unit

New diaphragm unit on left side, and old one on right.

Canon 99 error, disassembly canon 17-85 IS USM, change diaphragm unit

Get old one and unscrew 1 screw, after that remove metal guide.

Canon 99 error, disassembly canon 17-85 IS USM, change diaphragm unit

Done.

Canon 99 error, disassembly canon 17-85 IS USM, change diaphragm unit

Get new diaphragm unit, metal guide and 1 screw and assembly module. Flatcable under guide.

Canon 99 error, disassembly canon 17-85 IS USM, change diaphragm unit

All parts on the table.

Canon 99 error, disassembly canon 17-85 IS USM, change diaphragm unit

Assembly in reverse order. First off all place diaphragm unit into the zoom-tube, and fix it with sliders. After that place lens into the tube and fix it with sliders. Image stabilizer is last one. Parts orientation you can see on disassembly photos.

Canon 99 error, disassembly canon 17-85 IS USM, change diaphragm unit

Thank you :)

This post also available in Russian.

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