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Omega 1342 stepper motor oscillating back and forth

  1. Scootle Nov 6, 2023

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    The stepper motor (part #9400) isn't making a full step forward and then goes back on the next beat. The symptoms look rather like you get when the battery gets low but I have this on a test rig and powered by a power supply so it's not that. I have seen other discussions on this same topic elsewhere but none come to any conclusion as to why it would start to behave this way.
    Have any of you got any ideas or even better, solved this? Secondly, has anyone tried to take one of these things apart? It doesn't look serviceable but as they are as rare as hen's teeth in the marketplace I may as well have a look.
    Thanks in anticipation.
     
  2. Canuck Nov 6, 2023

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    I don’t have the answer to your problem that you seek, but the solution is to have a watchmaker check it out for you. But arrange a second mortgage first!
     
  3. Scootle Nov 7, 2023

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    ;) thanks for the advice Canuck. I am a watchmaker - but obviously not a very good one:taunt:
     
  4. JimInOz Melbourne Australia Nov 7, 2023

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    These movements are very finicky. Try disassembling and checking for crud/dried lube etc. Then re-assemble just the circuit and train wheels and see if it will run without interference. I also read that all parts not associated with the stepper motor should be demagnetised, this makes sense to me but I've never gone that far.
     
  5. Scootle Nov 7, 2023

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    Thanks mate - you've clearly been there before :). That's exactly what I did. In fact my test rig is completely disassembled because I too was convinced that it was magnetism from screws or base block etc. And like you I won't demagnetise the stepper motor itself because, I think, it has permenant magnets on the rotor (hence my comment about taking that apart too). It's a real mystery to me what else could cause it. 20231106_100951.jpg
     
  6. lejaune Nov 7, 2023

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    What kind of signal do you apply to the input between the blue and orange wire? If I remember correctly, to advance the motor by a step, the signal must be a positive pulse closely followed by a negative pulse. I don't remember the timing of the pulses, but it is described in a technical document which I don't have access at the moment. It is linked on the bottom of this page,
    https://www.watchrepairtalk.com/topic/10865-omega-1342-servicerepair/
     
    Edited Nov 7, 2023
  7. Scootle Nov 7, 2023

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    Great question. You are right about the reversing polarity of the signal. I had originally tried to step it by hand but failed so I wired those contacts up the the electronics module directly out of the watch and powered that up (and can watch it on a 'scope and it does what you expect). I have a video of that but the media upload on this forum only uploads from a few places so I have joined a facebook group and will upload it from there. Suffice it to say it still ticks half forward and half backwards just as Len suggests in that Watchrepairtalk thread. BTW thanks for that. I had seen an earlier conversation from Len on the problem but not that one so I will be going back to that now. Great to talk to someone who knows the problem though. Thanks.
     
  8. lejaune Nov 7, 2023

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    Have you also tried to run the motor in the movement with the train wheel bridge but without the intermediate wheel (or whatever the name of the wheel)? The idea is to let the motor run by itself without driving a load but still supported by both pivots/bearings. I see in your pictured test rig that the fan-like rotor is not supported by the top bearing/pivot. I don't know if that allows the rotor to move completely freely.
     
    Edited Nov 8, 2023
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  9. Scootle Nov 8, 2023

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    Nice try - tried it - no change :(
    p.s. I think I have managed to post the video of the fault
    https://www.facebook.com/reel/6970095423054536
    I think I am getting obsessed by this now. It's got to be something to do with the residual magnetism in the teeth of that rotor.
     
  10. sheepdoll Nov 8, 2023

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    Interesting I just ordered a 1342 movement off ebay that I have been watching for some time. The seller offered 20 bucks so I decided to take a chance. I have been wanting something I can do electrical tests on. I still want to see if I can get an arduino (Avr Tiny 88) to talk to one of these.

    I notice the links to the pdfs 1342_complet_4216.pdf, 1342_complet_2302.pdf, and 1342 complet test.pdf are borken on the watcrepair forums. Does anyone have a working link?

    Getting a naked movement violates my current guideline about purchasing complete watches with cases. Sometimes impulse takes hold. And I did give it three days of thought before pulling the switch.

    I would ask respetivly that people NOT post facebook (fadbook, greedbook, Livere de narcisist etc) links. Not everyone has an account or time to waste on such things. Such links also leave nasty tracker cookies behind what record info about people who do not have facebook accounts.
     
  11. Scootle Nov 9, 2023

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    Firstly, with regard to the Facebook link, the only way to add video to this thread that I could find involved the use of Facebook, LiveLeak, Vimeo or YouTube so I didn't have any option. If you know of an alternative please let me know.
    Secondly, the links to the pdfs worked for me so if you have a prefered method for me to get them to you, again, just let me know but presumably not posting them on Facebook.
     
    sheepdoll likes this.
  12. lejaune Nov 9, 2023

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    I believe you need to register to the watch repair website to gain access to the attached files.
     
  13. sheepdoll Nov 9, 2023

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    Most users upload You tube. Might have to wait 24 hours after creating an account.
     
  14. sheepdoll Nov 9, 2023

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    The site does not ask for a login to view attacments. It just states they were removed.
     
  15. lejaune Nov 9, 2023

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    It doesn't ask explicitly, but if you don't sign in, the files will show as "unavailable".
     
  16. sheepdoll Nov 10, 2023

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    I just created an account on WRT. Probably should have done so some time back. There are a few threads I read from time to time mostly relating to a DIY timegrapher.

    The 1342 movement should be here early next week. Given the price and desirability of some of the parts I am not expecting much. I do want to see if I can duplicate some of @Scootle work in talking directly to a stepper.

    I still think some of this will be the future of watch repair.
     
  17. studeb Nov 10, 2023

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    Can you check the coils? Are they all energizing?
     
    Scootle likes this.
  18. Scootle Nov 11, 2023

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    We should keep this thread of research going. I also have a replacement part on the horizon and intend to try swapping the rotor's to see if this problem is caused by the permenant magnet or the electromagnet (possible shorted turns!) .
    so I like this question I just don't know how to answer it.
    The failure mode suggests a weak electromagnetic force but when I removed the rotor as far as I could tell it only had one coil winding. I don't understand the design of this motor.
    How can I tell if the winding is shorted
     
  19. sheepdoll Nov 11, 2023

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    One of the things I want to do is to use the PWM of the AVR to put a high frequency onto the coils. Not unlike the way one puts similar signals onto the Ethernet magnetics. Or Pipe organ relay magnets. (which are also telephone switched networks.) The idea is to look for EMF reflections. All coils will have an impedance which is measured in ohms. It is a fundamental of the length of the wire which causes a voltage drop in a straight wire. When coiled the back EMF affects this.

    I see the data sheet list the coil resistance as 2 to 3 K ohms. Cheap digital meters often have fairly high current voltage. Usually the data sheet will give the impedance of the meter. Pipe organ magnets have resistances in the 10s of ohms and use voltages in the 12 to 25 range.

    The coil can also work like an antenna. So putting a frequency into one end and looking at the EMF can also be used to detect a broken coil. (or a bad network cable)

    There are plenty of watch timer testers out there what read this. I am sort of a do it yourself sort of gal, so am looking more at the challenge, or what to do wit a tray of left over AVR processors.

    Most of the time a coil breaks is near the contact terminals. Often the first few windings can be teased out. If there is an over current the wire will act like a fuse. This will melt through the weakest part which will be closest to one of the terminal as the electrons are acting like cars on a freeway all trying to merge past the narrow point. Sand in an hour glass does the same thing.

    I only have a cursory understanding about magnetics. Magnetic fields do have to have a completion pole. Ironically I was part of some patent discussions where this was discussed in front of me. This material is often pure sintered iron or nickel. Funny things go one with magnetics. There is something called spin. A friend of mine worked for IBM ins the spintronics dept. Rule no one is there are no quantum mechanics in industrial applications. IBM wound up calling the product 'Fairy dust." The curious thing is when electron spin is converted to light, the light is polarized. Such is what makes your hard drive work.

    See the data sheet refers to parts 1, 2 , 3 and 4 as a magnetic circuit. I think this is the same as the frame of a pipe organ magnet. Some of this is shaped and sintered into permanent magnets to complete these fields. And Maxwell's equations are hard to follow. Somewhere I have some green film what shows magnetic flux lines. When I get my watch I may try it and see if there is enough magnetism to leave a shadow.

    I suspect looking over the data sheets some of this is a bit obfuscated. While at the same time clearly drawn with a CAD application.

    The short of it this is what is called a BLDC motor. (Brush Less Direct Current) Which are really AC motors. There is quite a bit of theory written on these as most computer fans are such beasts. Modern automotive also uses them.

    I also bought some swatches to break up and see how they function. I noticed that the newer movements use mechanical setting. The magnetic clutch is novel to me and I still have not set my Tissot from the recent time change.

    IMG_4243.png
     
  20. lejaune Nov 15, 2023

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    I don't think this video link works.