Canon 70-200 F4 is Repair En

Canon 70-200 F4 IS disassembling, repair

Canon 70-200 F4 IS disassembling

The lens (probably) has been dropped down fr om a chair. Symptom: The stabilizer can be switched on, but switches off in a few seconds. The camera gives back no error code. After a deeper examination: If the camera is on a solid surface, so it is no need of sta bilizing, the IS works normally (but without sense, s ense, of course). For smaller moving seems to work, but after moving with a bigger amplitude, stops working (you can hear this through the typical IS-noise). A good IS lens after a fter depressing slightly the shutter button makes a fine high frequency noise. The defective one has a longer and louder sound. By a disconnected IS lens you can always here a fine clucking noise. In this one this sound was louder.

Copyright: Ruzsa János, [email protected]

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I was very interested to know, what happened to my lens, so I dismantled it. Anyway, I wanted even to save that ca 250-350 USD, which the official IS repair costs.

With the dismantled socket. The lens housing is made of plastic.

The upper black part is the IS unit with electronics, fix and moving lens.


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This is a position sensor for the zoom ring - practically gives a 5 bits digital information - non-linear.

The IS unit, with the disassembled gyro-sensors. I suppose that they are micromechanical chips, without any rotating parts.

The 2 sensors are mounted at a 90 degrees angle on the body


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This is the IS printed circuit board (PCB), connected with a cable to the main board.

After taking apart the PCB you can see the "engine" two plain solenoids, which are fixed on the moving lens, positioned at 90 degrees. They are connected to the PCB with two ribbon-cables, which permit the moving.

The moving lens is can be moved very easily in it's plane, +/- 3 mm (!) in each direction - but cannot rotate. So it has only 2 degrees of freedom.


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In this unit is a small motor too (at the left side of the picture). His function is to open and close the brake of IS unit, as I've found out later. The stabilizing effect is probably made by giving an opposite movement to the lens reported to the movement of the camera body. But how?

I suppose, that for this the solenoids should be supplied with a symmetrical signal, with a 50 % PWM, and relative high frequency, which pulls the lens in the middle of the magnetical field, and changing the PWM ratio the lens will travel to the right /left or up/down. The sound of this could you here when activating the IS (by half depressing the shutter button). Upper view


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On the backside of the PCB you could observe two IC-s, and exactly below them two small solenoids, on the body. I suppose this sensors can register the real position of the stabilizing lens group.. Magneto-resistive sensors, e.g..

The inner black ring is the mount or frame for the moving lens. It has 4 "teethes". When IS is switched on, they permit the moving (or sliding) of the lens group, because in the body there are it's bigger negative pairs, so the lens group will move +/- 3 mm, as the solenoid is driven by the IS control circuit. As I mentioned, the lens group is not able to turn around it's axis, this is prohibited by the special guide system.


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On the body, exactly around the moving part is this black blocking-ring, which is guided by 6 small pins to can rotate around it's own axis. 3 of them are even keeping it in the plane. Normally this ring can rotate very fine ca. 15 degrees, driven by a small step-bystep motor. After switching on the IS module, at first the solenoids are getting the control current, so they are kept in the middle by the magnetic force, after then the ring is rotated, deliberating the lens - after this the lens group will be hold only by the solenoids. The small white pinion on the axis of the step-motor rotates the ring through a tiny toothed sector on the ring. The rings end position is sensed by an optocoupler.


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After many disassemblingassembling I was not able to find the cause of the fault when I realized, that the longer noise by switching on comes from the small pinions motor, which is not able to rotate the blocking-ring. Fortunately, a stepper will not burn out in this case.

I found out, that the ring is too tight between the 6 pins strange, because the body and the pins are not adjustable. But on the ring I've found two small marks.

The source of this two marks was, that when the lens was dropped down, the stabilizing lens group forced the 1,5 mm thick blocking ring, which was cracked only partially.


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This was enough that the ring has been expanded a very little. With a small external force I've broken the ring - but this was intentional, as I wanted to take out some material, and then to bind it again with a very strong two-component adhesive. I roughened even the upper surface of the ring with some abrasive-paper (800) - putting the adhesive only on the broken surface could not held. My favorite is the Hungarian adhesive Uverapid A+B, which adheres practically to any material (metal, polyamide, glass etc), and in ready to use form is like the honey, so it will cover the small parts. The slip-gauge was necessary to set the right diameter in any direction, because the ring is easy deformable. There is no second try… But the adhesive needs an hour to be hard, for this period the parts must be hold precisely in the right position. I put some double sided adhesive tape on an original CD (they are of a very strong material, and normally perfectly plane). The adhesive tape should be not to strong, otherwise I will not be able to get down the ring.


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I put some copper wire on the upper surface - "metal reinforced-adhesive". For the maximum safety I made the same "reinforcing" on each thin section. The next day I mounted the ring in it's place - the lens worked fine on the camera..

Moral of the story: The Canon L lens has a … plastic housing. This was probably not so bad, because the plastic was damping the shock, better than a metal. If you get some dust in the lens, is absolutely not so complicate to disassemble the lens. The gyro sensor is NOT a mechanical rotating unit, but a microchip, so what we can here during the functioning, is the noice made by the working solenoids. If you don't need it, shut off the IS , because otherwise on each half pressing the shutter button it will de-blocking the ring, and after a few seconds blocking it again - and this is absolutely meaningless. You must determine, how long you can held the camera in your hands without blurring the image. For me on the Canon 30D (1,6 x crop) I can use the reciprocal rule: 200 mm zoom position is working well with 1/200 seconds. And at last: don't drop down your lens.

Ruzsa János (Budapest, 08.10.2009)

Case You have found this material useful, please send me an e-mail.


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Canon 70-200 F4 is Repair En

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