How long would your HSM motor last?

Started Jan 23, 2013 | Discussions
BozillaNZ Regular Member • Posts: 346
How long would your HSM motor last?
12

How long would your HSM motor last?

edstudios@hotmail.com

January 23, 2013

My 2 years old Sigma 50mm 1:1.4 EX DG HSM has recently gave up the ghost by no apparent reason. AF turned from good to sluggish and finally stopped moving at all. When I half press the shutter button I could hear slight ticking sound coming from the lens but it would not move. As I like to take stuff apart and try to fix them, or at least learn what's wrong with it, I couldn't help but to take it apart.

First impression: the materials used are very good, all internal tubes are made from metal, unlike the Canon one which is mainly made from plastic. The focusing cams are very percisely machined, with very tight tolerances and smooth movement, which is very good sign.

However, each time after I took apart and re-assemble the lens, the AF would start working for a short period, say a week at the beginning, then it got worse. Re-assembling the HSM motor would only make the lens AF working for a day. It would stop working in the next morning when I pick up the camera again, very frustrating.

I had to dig deeper to see what really went wrong with the lens. The glass unit moves smoothly with hand, so there is obviously no problem on that part. The HSM motor is actually very simple in construction, two pieces of metal rings pressed against each other, one with teeth and pizoelectric material to generate vibration. What can go wrong with this?

I have to mention that I have disassembled dozens of Canon's lens, fixed broken flex cables and added lubrication to the sliding parts. But not a single one had a USM failure. The Canon USM's construction is very similar, but both the rotor and the stator are made from aluminum, as far as I can tell.

This Sigma HSM looked weird to me. The stator is made from golden colored material, seems like brass or some alloy with copper. The rotor is aluminum but the surface is coated with a lousy paint job, like a thick layer of black paint being sprayed on the surface.

Since the AF is broken, there could be three items that can potentially be faulty: 1. the driving circuit on the PCB. 2. The stator, 3. The rotor.

I had to narrow down where the problem really lies. I put the stator on a hard table surface, teeth side down, connected it to the PCB and hold the PCB connector to my Canon camera with the PCB dangling between the camera and the HSM stator (dangerious move, do not try it at home). Turned it on and half pressed the shutter button. To my surprise the stator vibrates on the table and tried to rotate. Because the contact force is too low, it only moved very faintly. I tried to press it against the table using my hand and I got an electric shock (!) to my fingers. Apparently the alternating current passes easily through my body and shocked me! I then put a lens cap on the stator, acting as an insulator and tried to AF again. Now with good force applied on the rotor, the movement is very strong. Conclusion? The PCB and stator are both good!

The problem must lie on the rotor. How could a piece of metal ring having any problem? After careful inspection it comes as a shocker: The rotor uses black paint to act as the contact wear material! After using it for a while the paint will inevitably get wear out, them HSM will then stop working. Why do they need a layer of paint? Canon's USM doesn't need paint, Nikon's SWM doesn't need paint, why does HSM need it?



I went ahead and sanded off the paint layer, exposing the bare aluminum on the ring. After some careful polishing with wet P1200 sand paper and 3M P2000 rubbing compound, I though I did a good job reconditioning the rotor surface. After reassembled the lens back together, it started AF just fine! I was over joyed with my achievement, thinking that I fixed my lens for good. However, things didn't last long. After only 2 days of sparse use, the AF stopped again. Same sympton: ticking sound when lens was trying to AF. I had to strip the lens down the the HSM part again. Apparently the rotor and stator has jammed up. Previously I was able to manually rotate the rotor when it is mounted on the lens, but now it is firmly fused with the stator! Until I took the pressure spring off and separate the stator and rotor again.



After careful inspection, it seems that the stator (golden teethy part) is made from a harder metal than the aluminum rotor, and when running in bare metal, it will scortch the rotor and create metal shavings. Those shavings accumulate and made bigger scortch in both the stator and the rotor, finally caused them to seize.

Now the result is clear: The HSM needed this layer of spray paint to work properly. The paint provided scortch free friction interface. I now have to order new HSM parts to get my lens fixed. But how long can a new layer of paint last? Do a search on the internet and you will see a lot of similar symptoms of HSM suddenly stop working and giving faint ticking sound. I love the Sigma 50mm lens in terms of optical performance. My copy's AF accuracy is also good after body AFMA. But knowing that the entire HSM mechanism rides on a thin layer of paint, I'm not sure I am confident enough to invest on another Sigma lens.



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photonius Veteran Member • Posts: 6,850
Re: How long would your HSM motor last?

nice analysis!

BozillaNZ wrote:

How long would your HSM motor last?

edstudios@hotmail.com

January 23, 2013

My 2 years old Sigma 50mm 1:1.4 EX DG HSM has recently gave up the ghost by no apparent reason. AF turned from good to sluggish and finally stopped moving at all. When I half press the shutter button I could hear slight ticking sound coming from the lens but it would not move. As I like to take stuff apart and try to fix them, or at least learn what's wrong with it, I couldn't help but to take it apart.

First impression: the materials used are very good, all internal tubes are made from metal, unlike the Canon one which is mainly made from plastic. The focusing cams are very percisely machined, with very tight tolerances and smooth movement, which is very good sign.

However, each time after I took apart and re-assemble the lens, the AF would start working for a short period, say a week at the beginning, then it got worse. Re-assembling the HSM motor would only make the lens AF working for a day. It would stop working in the next morning when I pick up the camera again, very frustrating.

I had to dig deeper to see what really went wrong with the lens. The glass unit moves smoothly with hand, so there is obviously no problem on that part. The HSM motor is actually very simple in construction, two pieces of metal rings pressed against each other, one with teeth and pizoelectric material to generate vibration. What can go wrong with this?

I have to mention that I have disassembled dozens of Canon's lens, fixed broken flex cables and added lubrication to the sliding parts. But not a single one had a USM failure. The Canon USM's construction is very similar, but both the rotor and the stator are made from aluminum, as far as I can tell.

This Sigma HSM looked weird to me. The stator is made from golden colored material, seems like brass or some alloy with copper. The rotor is aluminum but the surface is coated with a lousy paint job, like a thick layer of black paint being sprayed on the surface.

Since the AF is broken, there could be three items that can potentially be faulty: 1. the driving circuit on the PCB. 2. The stator, 3. The rotor.

I had to narrow down where the problem really lies. I put the stator on a hard table surface, teeth side down, connected it to the PCB and hold the PCB connector to my Canon camera with the PCB dangling between the camera and the HSM stator (dangerious move, do not try it at home). Turned it on and half pressed the shutter button. To my surprise the stator vibrates on the table and tried to rotate. Because the contact force is too low, it only moved very faintly. I tried to press it against the table using my hand and I got an electric shock (!) to my fingers. Apparently the alternating current passes easily through my body and shocked me! I then put a lens cap on the stator, acting as an insulator and tried to AF again. Now with good force applied on the rotor, the movement is very strong. Conclusion? The PCB and stator are both good!

The problem must lie on the rotor. How could a piece of metal ring having any problem? After careful inspection it comes as a shocker: The rotor uses black paint to act as the contact wear material! After using it for a while the paint will inevitably get wear out, them HSM will then stop working. Why do they need a layer of paint? Canon's USM doesn't need paint, Nikon's SWM doesn't need paint, why does HSM need it?



I went ahead and sanded off the paint layer, exposing the bare aluminum on the ring. After some careful polishing with wet P1200 sand paper and 3M P2000 rubbing compound, I though I did a good job reconditioning the rotor surface. After reassembled the lens back together, it started AF just fine! I was over joyed with my achievement, thinking that I fixed my lens for good. However, things didn't last long. After only 2 days of sparse use, the AF stopped again. Same sympton: ticking sound when lens was trying to AF. I had to strip the lens down the the HSM part again. Apparently the rotor and stator has jammed up. Previously I was able to manually rotate the rotor when it is mounted on the lens, but now it is firmly fused with the stator! Until I took the pressure spring off and separate the stator and rotor again.



After careful inspection, it seems that the stator (golden teethy part) is made from a harder metal than the aluminum rotor, and when running in bare metal, it will scortch the rotor and create metal shavings. Those shavings accumulate and made bigger scortch in both the stator and the rotor, finally caused them to seize.

Now the result is clear: The HSM needed this layer of spray paint to work properly. The paint provided scortch free friction interface. I now have to order new HSM parts to get my lens fixed. But how long can a new layer of paint last? Do a search on the internet and you will see a lot of similar symptoms of HSM suddenly stop working and giving faint ticking sound. I love the Sigma 50mm lens in terms of optical performance. My copy's AF accuracy is also good after body AFMA. But knowing that the entire HSM mechanism rides on a thin layer of paint, I'm not sure I am confident enough to invest on another Sigma lens.



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VREN Regular Member • Posts: 111
Re: How long would your HSM motor last?

Thank you so much for taking the time to share your experiences. Great post.

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photonius Veteran Member • Posts: 6,850
Re: How long would your HSM motor last?

VREN wrote:

Thank you so much for taking the time to share your experiences. Great post.

This could brew into a big headache for Sigma, if more and more HSMs fail. Probably they have to improve their HSM design.

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WhoAmI5423 Forum Member • Posts: 93
Re: How long would your HSM motor last?

Now I'm getting worried about my Sigma 85 :-/

Great job with the write-up though!  Made for a very good read!

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victorian squid
victorian squid Veteran Member • Posts: 3,391
Re: How long would your HSM motor last?

Thanks for the post!

And, Yikes!

As much as I love Sigmas, this certainly gives me pause. Sure, it's entirely possible other models aren't constructed the same way, but it's just as likely they are.

Although the next lens I have my sites on isn't necessarily a Sigma - I'd sure like to hear a bit more about this. Especially in light of that new 35 f1.4! Then again, I've got a 4 Sigma's, 2 are getting pretty old, my 10-20 has tens of thousands of clicks on it and no problems.

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photonius Veteran Member • Posts: 6,850
Re: How long would your HSM motor last?

victorian squid wrote:

Thanks for the post!

And, Yikes!

As much as I love Sigmas, this certainly gives me pause. Sure, it's entirely possible other models aren't constructed the same way, but it's just as likely they are.

Although the next lens I have my sites on isn't necessarily a Sigma - I'd sure like to hear a bit more about this. Especially in light of that new 35 f1.4! Then again, I've got a 4 Sigma's, 2 are getting pretty old, my 10-20 has tens of thousands of clicks on it and no problems.

but those probably don't have an HSM motor?

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victorian squid
victorian squid Veteran Member • Posts: 3,391
Re: How long would your HSM motor last?

photonius wrote:

victorian squid wrote:

Thanks for the post!

And, Yikes!

As much as I love Sigmas, this certainly gives me pause. Sure, it's entirely possible other models aren't constructed the same way, but it's just as likely they are.

Although the next lens I have my sites on isn't necessarily a Sigma - I'd sure like to hear a bit more about this. Especially in light of that new 35 f1.4! Then again, I've got a 4 Sigma's, 2 are getting pretty old, my 10-20 has tens of thousands of clicks on it and no problems.

but those probably don't have an HSM motor?

Yes, 3 do have HSM motors - especially the 10-20!

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BTW, I see that this article has been posted on The Digital Picture.

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Manny E Forum Member • Posts: 82
Re: How long would your HSM motor last?

Nice post BozillaNZ. I have a 70-200 HSM II which I loved, the AF stopped working after around 30k shutter actuations. I really would have wanted to try Sigma again because their optics supposed to have improved even more recently but my experience with the AF motor failure will always give me pause.

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Daniel Lauring
Daniel Lauring Veteran Member • Posts: 9,342
Re: How long would your HSM motor last?

Great info.  I wonder if a di-electric grease would be a solution...something thick enough to stay in place.

Roger Krueger Senior Member • Posts: 2,785
Re: How long would your HSM motor last?

For those of us slightly less brave—how much does Sigma service charge for this? Where are they? I'm spoiled being in Orange county all the time and thus able to drop off my broken Canon bits in Irvine.
My Canon 50/1.4 is certainly a fragile P.O.S., but it's cheap and convenient to fix. Still, 6 AF kills in 8 years was enough, just got the Sigma a couple of weeks ago, hoping for less drama.

Brev00
Brev00 Veteran Member • Posts: 9,305
Re: How long would your HSM motor last?

Sigma is in New York.  They recently repaired the os unit on my !7-70 and returned it in less than two weeks under warranty (2 years old).  I have no idea how much they might charge for the issue discussed here, but I resist worrying about such things. I was enjoying my 17-70 while in Hawaii when the os unit failed.  I had another lens with me and I still got my share of shots.

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ScottD1964 Senior Member • Posts: 1,914
Re: How long would your HSM motor last?

Why did you attempt the repair yourself?  Don't most Sigma lenses (including the 50 f1.4) have a 4 year US Warranty?

I 've purchased 4 Sigma lenses over the last two years and all had 4 year warranties, 1+ 3 yr extended US.

Scott

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yray
yray Senior Member • Posts: 1,726
Re: How long would your HSM motor last?
1

I have several Sigmas, five of them HSM, none has failed so far. If/when it fails they'll fix it, -- with Sigma it is not a big deal, they have a good service department. I'm more worried about my Nikons.

Antony John Senior Member • Posts: 1,252
Re: How long would your HSM motor last?

Interesting and informative article. Thanks

Always wondered how these motors worked, now I have some insight.

Aluminium is difficult to coat and requires specialised paints.

If you have a company near you that makes non-stick kitchen products maybe they could coat it for you? They'll use teflon coatings and these have a low coefficient of friction which would be ideal.

Alternatively try 2 pack epoxy glue (low viscosity variety). Doesn't matter what the colour is and clear would be OK as well (though difficult to see if you've coated everything or not). Mix small portions, coat ring with a nail varnish brush (no, nail varnish itself won't work - well not for long anyway). Allow to cure 24 hrs in a warm place (or put in an oven at say 60°C for about 2 to 4 hours - higher temperatures might distort the Al), sand with 1200 water paper. Repeat if necessary.

In the later case if your Al ring is damaged you might have to build up a few layers of epoxy glue to get the surface flush again (obiosuly use a flat surface - like glass - for the sanding surface - with which you can also use the polishing paste for finishing too).

Epoxy paint (2 pack) would be better because the viscosity will be lower but depends if you can get small quantities. The film build will be lower than with glue which is a problem if you have surface damage to 'fill-in'.

Don't mix more epoxy than you need per step - it'll go hard and be unusable.

No, haven't tried this myself but should work if properly done. Longevity would need to be experienced I guess.

HTH and good luck!

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OP BozillaNZ Regular Member • Posts: 346
Re: How long would your HSM motor last?

Some update: I've got the new HSM rings and put them on by Feb 2013, now I only use this lens occasionally. So far so good. However this has put me off from buying any new lenses from them, until I can get some disassembled pictures to see if they have even tried to update the construction of their HSM motors. The Canon's Ring USM on the other hand is very well made. Simpler and more robust. I just wish the HSM could be as fine as Canon's.

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