USM refurbishing

Cleaning of the optical encoder ring helps only the focus hunting cases.
When the problem is with the usm ring, I refurbish them with degreasing, polishing both rings to get back the plane, shiny surfaces, then cleaning again, after which mounting together.
When mounted, you have to try to rotate the plastic/metal ring relative to the metal one. IT MUST have a high frequency sound. Case not, just rotate them, till you get that annoying noice. This brings together the surfaces very close, so they adhere to each other – and USM starts working.
Here you see my small polishing tool, made of an old HDD disk, which is the best plane, which you can get, and a battery screwdriver. Use some alcohol for moistening! Polishing paper: 2000.

About canonrepair

Ruzsa János. Amatőr fotós, Canon DSLR váz. Amateur photographer. Canon DSLR user.
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28 Responses to USM refurbishing

  1. Ted Lindström says:

    Hi, thank you for writing this blog post as there is little information out there on how to refurbish canons ultrasonic motors. I own a Canon EF 500mm f/4 IS USM and got a crack on the “optical encoder ring” that I tried to fix myself. I glued it together and polished the surface to get rid of any excess glue.. Low and behold, the polishing made the encoding disappear and here I am, asking you for some guidance.. There is no usm replacement parts available for this lens anywhere so I was thinking that perhaps I can use the encoding ring from a different lens or create one on my own somehow. What do you think? I was also wondering what the encoding ring is for and how it works? Please help me. Kind regards, Ted

  2. Tom says:

    400 USM f2.8- the old version of this lens uses focus by wire. There are only a few persons who can dismantle this usm part; it´s completely different to the newer versions with “IS”. The usm gets stuck. The stator is “grabbing” into the hard coated aluminium surface of the ring. So you have to make this surface plane/flat again. You will need a microscope, a really flat surface and a very fine polish paste for grinding. Not a paper or something like that. Remember: the hard coated surface is only in a µm area! After that you will have a normal aluminium (that will be the end…). The way to bring back life will be the same for all USM with the rotating problems. But for the IS-type you will find spares in china or the usa.

  3. Mouloud Ilbouche says:

    Hi, I have a 70-200mm F:4L is usm, that had a slipping auto focus ring, i opened it cleaned the usm ring and the aluminum ring with alcohol then tightened little bit the tension spring and assembled works for a few days then stopped working no response at all, opened again i loosened little bit the tension spring then the usm worked for few days then stopped working, i can not find out if the problem came from the usm motor or the main electronic board any help will be appreciated. thanks in advance

    • canonrepair says:

      At first: alcohol is a great solvent – but here is not good enough. Try to use breake-cleaner spray – you can find it anywhere.
      Secondly: the two surfaces MUST be not only clean, but even VERY plane. This is why you have to polish them, and after polishing, and after mounting to rotate one against the other, till starts to squeak. THAT is the moment, when the two surfaces adhere to each other, and the work well.

      • Mouloud says:

        Thank you very much , I’ll give it a try, but i need some clarifications, after mounting you mean assembling totally the usm motor then i have to rotate the aluminum ring against the usm ring till starts squeak, is that right? then whats about the tension of the spring should i tighten it to its max or midway is enough.

      • canonrepair says:

        I always tighten the USM ring to maximum.
        Squicking comes only after having perfect plane surfaces, and some relative movement between the rings, which you have to make with your hands, to work them together, like an artificial wear – this will make the perfect sticky contact.

  4. wjh says:

    I have a canon 400mm f2.8 is, when I press the auto focus sometimes there is a smooth squeaking sound like metal being scratched, but when I turn the manual focus by hand and press the auto focus again sometimes the squeaking sound disappears and one day it will reappear. The question is, do you know what the problem is? Thank You

    • canonrepair says:

      could be the USM, but in fact I should here it, see it.

      • wjh says:

        If the problem is usm, what do you think is usually the cause? Incidentally, this lens has never been dropped or bumped and the focus speed and accuracy are still good

    • Tom says:

      The 400/2.8 USM IS uses the big USM. There are no spares longer available. This sound comes before it stops working. To solve the problem you have to rework the Alu-actor ring. The surface to the Stator is hard coated with less µmm. It is necessary to make this surface plane again and to be carefully with grinding. A glass plane with a special fluid… Only to strengthen the tension will have only a short success. The spare package from Vs. II will not fit for Vs. I (changed frequency).

      • wjh says:

        what is the next effect if left? in terms of speed and accuracy of autofocus this lens is still good

      • canonrepair says:

        After some time will slip too much, be slower, and at the end will not find focus (as will run out of the given time-window)

      • wjh says:

        I have another question, I use a canon 7d body and the lens is 400mm f2.8, sometimes when the camera is turned on and immediately presses the shutter button or the camera’s AF button to respond to the lens autofocus rotation, I have to press it 2x. …. is this a problem? If so, where is the problem? Thank You

  5. Matthew Svoboda says:

    Hello. I have a USM with a broken flex cable. Is there a way to remove the old cable, and replace it with a new one?

    • canonrepair says:

      You can not REPLACE it. Just cut at approx the half length (2 mm longer then the half), the donor cable too (2 mm longer then the half), after which you have to clean the cutted ends to eliberate approx 3-4 mm of copper, that you can put them one end on the other, overlapped, solder them toghether, and isolate with some tape. As the donor cable will lay reversed on the original, even the end will be reversed – but don’t worry, the USM socket makes contact on both sides.

      • Matt s says:

        Unfortunately the damage is to the the contacts on the ring. So I was thinking of having a new flex pcb made, and attempting to solder it to the ring. If this is not possible, then I can try to find another ring that is the same size. Do you know what other Canon lenses use the 77mm diameter USM

      • canonrepair says:

        No ideea. In such cases I go to my own scrapheap, and I try to find something similar 🙂
        This is of course no scientific method – can work or not.

      • Matthew Svoboda says:

        Have a 77mm usm you’d be willing to sell? Or a complete focus assembly for a 600mm f4 usm (non is)

      • canonrepair says:

        I have to check, if I have something right now. Do you live in the EU?

      • Matthew Svoboda says:

        No, but if you had the parts, I’d be happy to pay shipping.

  6. Mark says:

    Made the same experience as Toni Hallikas. If the USM “dies” its almost always either loss of spring pressure between rotor and stator or one of the conductive silver paint dips went bad.

    • canonrepair says:

      “…If the USM “dies” its almost always either loss of spring pressure between rotor and stator or one of the conductive silver paint dips went bad….”
      No, definitely NOT. MOST of them are only worn/contaminated with grease, and so repairable.

  7. Tom says:

    Ok, a way which is new… I´m always cleaning the strator only with alcohol. This part is only “dead” if the glued flex has lost its contact. The main reason for a stop is always the aluminium ring. Have you had a close look to the surface through a microscope? The surfarce is hard coated. This goes not through; it´s only less than half a mm. And there are some “springs” – one is the rubber between the plastic/metal and the aluminium, the second the shape of the ring itself. So if you want to get it back to life, you should only cut 0.1mm or less from that surface. A glass plate and a fine grinding fluid is a good solution, cause you have to cut that from the complete surface. For retention i connect the usm to an old usm lens. This helps to set the correct tension without a repeated teardown…

    • canonrepair says:

      I´m always cleaning the strator only with alcohol. – unfortunatelly alcohol is not a too good degreese.
      Use brake-cleaner. It is a strong degreaser, and is always clean, as it is under pressure. And cheap too.
      With the checking after refurbishing is an important ideea, i also do it sometimes, has sense to make a small test-wiring, not to damage the cables during the test.

      • Tom says:

        You can use an old 35-105 USM which is on ebay for 30€. To make it simple: i have soldered longer cables outside the optics and use an old plug from a died board. Now, i can take a canon cam with this optic and connect it with an USM outside. Cause having not all signals you have to turn the MF ring of the optic to get a movement. This should only help to determine if the usm will generally work or not. With the real signals an the force from turning the glass it´s completely different.

    • Toni Hallikas says:

      I have had some stators which has lost contact. It is typically those small conductive paint dips which are cracking open or high resistance. Just scrap the old fragile paint off, clean it and repaint with high conductivity pure silver paint.

    • Peter says:

      What tension would you consider correct? From my experience you can sometimes turn the retention ring above the spring of the USM all the way in to apply maximum pressure and the motor still works fine. I’m never really sure when the tension is right or maybe too strong or even if the pressure can be too strong at all (apart from a state where the stator can no longer move the rotor of course).

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