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 from 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 stabilizing, the
IS works normally (but without sense, 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 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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Canon 70-200 F4 IS
disassembling, repair
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.
Copyright: Ruzsa János, [email protected]
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Canon 70-200 F4 IS
disassembling, repair
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
Copyright: Ruzsa János, [email protected]
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Canon 70-200 F4 IS
disassembling, repair
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.
Copyright: Ruzsa János, [email protected]
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Canon 70-200 F4 IS
disassembling, repair
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
Copyright: Ruzsa János, [email protected]
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Canon 70-200 F4 IS
disassembling, repair
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.
Copyright: Ruzsa János, [email protected]
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Canon 70-200 F4 IS
disassembling, repair
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.
Copyright: Ruzsa János, [email protected]
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Canon 70-200 F4 IS
disassembling, repair
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.
Copyright: Ruzsa János, [email protected]
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Canon 70-200 F4 IS
disassembling, repair
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.
Copyright: Ruzsa János, [email protected]
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Canon 70-200 F4 IS
disassembling, repair
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.
Copyright: Ruzsa János, [email protected]
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