Rewiring damaged coil of a Dual motor

[Dan75]

Some time ago I managed to be too careless in servicing a Dual 1019 turntable motor. This motor is told to be in need of servicing as it contains disintegrating foam material,
used for dampening and seating for the motor shaft bearings.
Also many times the shaft and bearings have gotten too dry over time and need cleaning and re-lubricating.
That being said, I was attempting to pry the two motor housings apart but you could say I kinda failed there.
These halves were so tight pressed onto the coil that I had to use something to pry the halves apart step by step.
And that is where things went astray. I was not careful enough in looking where the prying tool was going when I finally reached my eureka moment after too long fiddling.

All this resulted in two damaged coils. In another topic I already discussed some of this but now I want to find out IF it can be rewired and if so, if it is economically worth it.
I don't know where to source it from in my region and what the costs will be.
Next post I will add some images.

[Dan75]

Images

[Dan75]

3rd image

[Dan75]

Top view

[Kleinstein]

There are companies that repair motors, though usually the larger (e.g. 3 phase 1 Hp und up) ones. The motor shown may be a the small end of what they can do, and the wire is also quite thin.  I have send motors for rewinding and at least for the local company the prices were reasonable, like some 30-50 EUR  (could be a special price for local neigborhood). Not really worth it for a standard motor, but a realy option for more special ones.

[andy3055]

The pictures are a bit out of focus to see the extent of the damage well. Take a shot at an angle so the light does not reflect off of the wire. Like I mentioned in the other thread, if you can make sure there are only a couple of turns broken/damaged and the rest is good and the insulation is intact, you can splice those broken turns and insulate them. Make sure to splice the corresponding left/right of the broken turn. You can use some heat shrink to insulate the joint.

Check your in box.

[Dan75]

Another motor in a Dual 1019 turntable was having difficulties in starting up recently. I noticed that after a period of say hours the motor had problems starting.
When I gave the pulley a little nudge by hand, it would spin.

Yesterday after playing for a longer period of time, I disconnected the power cable from the wall socket and when I stuck it back in, the motor was not responding at all.
I took it out, but it seems it is dead as a dodo?
Is there a way to check if it really is? is the same type as in the images. European model.
Could have been drawing to much current? It isn't protected by a fuse I believe, so if it is done for, are there any signs to look for?
Burn marks, smell, anything?
Man, I'm having no luck with these things

[TurboTom]

When looking at these small tangential sheet metal links (springs?) between the tips of the pole pieces, I'm almost certain that the pole pieces are removable. I guess the coils have been wound individually on a mandrel, insulated by wrapping tape/paper and formers around them and then inserted into the lamination. By removing the metal links (possibly after heating the stator to soften the varnish it's covered with), a disassembly should be possible and the repair wouldn't be too difficult. You've got to analyze a good coil to identify the number of turns and record the winding direction and interconnection. If it's worth the effort is something that you've got to answer to yourself  .

Good luck,
Thomas

[andy3055]

Dan,
As for the motor stalling after some time, it is a mechanical issue. If the motor was burnt, it will not spin after you give it a push and the windings will have a burnt smell. The chances are that the bearings are dry (unless there is so much dust between the stator and the rotor that is creating a mechanical obstruction). Just dismantle the thing, clean all the crud from the shat ends of the rotor and the bearings. Do not use any sand paper like stuff! These kind of motors usually have bush/sleeve type bearings and they are sometimes mounted with some sort of a felt packing and a retaining metal thingy that helps to self-center the bearing. After cleaning and re-assembling, lubricate with a light oil like sewing machine oil. Spin it and see if it will spin freely. If not, just slightly loosen the screws holding the bearing holding end "plates" and tap the shaft ends with a piece of wood or the plastic handle of a screw driver and the rotor will align itself so that it will spin freely when you try with your fingers.

[james_s]

Many motors have a built in thermal fuse, if they stall for too long and overheat this fuse will blow and the motor will be dead. Check the resistance of the windings and see if the motor is open circuit.

[Dan75]

Hi all, thanks for the input!

What I forgot to mention is that the second motor that I wrote about in my previous post, the one that does not want to spin anymore, was a rebuilt one.
There is a manual about these motor revision made by some guys that explain in detail how to proceed. I did this, more than a year ago. All was fine until now as I'd explained.

There is no dust, no crud, nothing in there. I do not smell something burnt.
Yesterday evening (different time zone here ) I took the motor apart to see inside. Nothing to see, no damage on the shaft, windings, bearing etc.
I double checked the functionality by connecting the motor to another but exact same switch that these motors are hooked up to from factory, still did not work. Tried another, 3rd motor on that same switch, and that one spins.
So my guess is that it could be what james_s writes, the thermal fuse maybe?

I took my MM, and tested the wiring on it, the ones that run from coils to the switch, they seem ok to me.
But when I tested in Ohm mode, I got a reading on the yellow and brown wire of around 490 ohms, but the white and black got no result.
What does that mean? Can it be saved?

[andy3055]

I am not sure how the windings are configured. But it is possible that there is a thermal fuse on that winding that is supposedly open. It is also possible that one end of it has got disconnected from the lead out-either the white end or black end. Inspect the connections to the leads and make sure nothing is broken/disconnected.

So, are the pictures you posted of the same motor or an identical motor you are now talking about? I ask this because I feel that the motor in the pictures is a shaded pole motor. If it is so, why does it have two separate windings? A shaded pole motor does not need a separate winding like in the case of a split phase motor where one winding is fed through a capacitor. Or, is it that the motor has two windings for the two speeds? That does not make sense as it will need a complicated switching arrangement and I have never seen anything like that. Usually, a motor in this type of application runs at constant speed and the speed change from 33 1/3 rpm to 45 rpm, is done by mechanical means. Having said that, this being a Dual-German made machine, anything is possible. Germans always had some ingenious ways of complicating stuff!

I once had a Lenco turntable that had a tapered thingy on the end of the motor shaft and the idler wheel could be set at any point on the taper so the speed could be varied not is steps but could be set to any speed one wanted! The motors in turntables I have seen always had shaded pole motors and either a tapered like above or stepped thingys on the motor shaft to change the speed along with the idler that goes between it and the inside rim of the platter.

[Dan75]

I love you guys, thank you so much for your help!
But just now I think I know what has caused the problem.
The two motor shells are kept together by the use of 2 bolts and 2 washers + nuts.
They run through the shells inside a protective sleeve made of some sort plastic.
I looked at the sleeves and saw a small hole in one of them. And guess what, it is situated just right where the coils are.
And on that spot which is hard to see because one shell is still on the coil and difficult to take off, I can see something that looks like there is
something going on, looks damaged. Great, another one down the drain. But how the heck could that happen in the first place, I mean, I never took it apart until it died on me
and I wanted to look what had happened.
The hole in the sleeve looks like it has burned through, like it is scoured.

[andy3055]

So, it has shorted to the core or the bolt? Interesting. True the blots are usually very close to the windings but they have enough space not to short circuit. Once you disassemble and repair, put loose pieces of heat shrink on the bolts before re-assembling.

These motors are pretty simple and easy to fix unless they have complicated electronic speed controls, which I have not seen.

[andy3055]

I just downloaded the service manual for the 1019. The motor is a dual voltage 110/220 volts. This is why you have 4 leads. Just did not think of it myself! 

So, keep us informed on how you proceed.

Here is a link for the manuals: https://www.vinylengine.com/library/dual/1019.shtml

You need to create a free account, but worth it. The wiring diagram is there in the service manual link.

[Dan75]

Hi Andy, I have taken some photos of the damage, hope it is a good view.

[Dan75]

It looks like there are about 10 wires or so broken.
You say it is easy, but the wires are very small and how do you know which ones were connected.
And it needs to be connected but isolated as well

And indeed, it is a 110/220 volts motor with 4 wires.
The white / black is done for so that is why it won't power up. But I am still baffled by why it happened.
I seriously did not touch the screws on it, so why the heck it got damaged is a mystery to me as well as why it stopped working earlier but spinned back up again when you gave the pulley
that sits directly on the motor shaft a nudge.

[james_s]

The only practical way to repair this is to remove the damaged coil, wind a new one and replace it. How difficult it is to disassemble the motor enough to do this varies widely.

[wasyoungonce]

The motors made to be taken apart with those dark metal spring clips.   This allows those copper springs to relax and remove the windings.  They will all be lacquered but its doable.

[andy3055]

It is not impossible to repair it in place but James is correct. The best is to rewind that coil. See the post by Wasyoungonce. He has explained the steps on how to remove the coil. Just make sure to put the copper ring back in place as it is because it is a single turn winding that creates the shaded pole which provides the phase splitting.

Do you have a place to buy the magnet wire? If not you could order on line. Make sure to get the gauge properly from an undamaged/crushed piece that you first burn (Use a candle flame. If not you will heat it way too much.) to remove the insulation and the varnish.

On the other hand, you can try a motor winding place or source a new motor from one of the Dual service centers.

[andy3055]

Here is another thought. If you can get the coil out without damaging, you can start unwinding the turns from the top end, Since the damaged turns are almost all on the top, you might be able to get to the last "good" end without much trouble. If you plan on that, just count the number of turns you are removing and rewind the same number of turns with the same gauge. This way, you have just one splice. In fact, you should be able to do this even without removing the coil!
After doing the repair, make sure to use insulating varnish and bake it  with a high wattage light bulb!

[Psi]

If it was me, and I was motivated to fix it, i would probably attempt to just add new wire sections between all the broken wires without unwind it.

I think under a microscope you could solder new lengths in with tiny heatshrink at each end and seal with high temp epoxy once joined back together and continuity looks ok.

Would have to be a bit careful to join the right ends together. but i think its doable.
And you'd want to cut and join any wires that look even partially damaged.

I guess it depends how much your time is worth. Probably a days work.

[wasyoungonce]

Getting the right ends together will be impossible.......andy3055 is right unwind till no more damaged wires......join in new enamelled wire (be sure to re-varnish the join.....and rewind on the number of turns you tool off .....

Hey...its borked now why not try.   I have rewound some small brushed motors....not easy but worked.  Varnish after to secure coils.

[Ian.M]

Getting the right ends together will be impossible.......

Not impossible at all.  Isolate the winding, and two of them can be identified by continuity testing from the winding ends, then individual broken turns and sections of a few turns can also be identified by continuity testing.  All that is required is to reconnect every turn in series without any shorted turns, so all that has to be done is check that each pair of ends you are about to join do *NOT* have continuity before joining them.   

However its going to be a tedious *PITA* to join and insulate them all neatly enough to be reliable and still fit in the housing so your and Andy's suggestion of a partial rewind is probably preferable. It would be worth seeing if its possible to only strip and rewind the damaged turns rather than unwinding from the winding end.  If the O.P's very lucky, It *MAY* just be possible that none of the broken turns are buried.  If any are, unwind from the end as Andy proposed.

[james_s]

It really isn't that hard to wind a coil like that from scratch. You can buy magnet wire online, and build a form out of wood or whatever you are most comfortable working with, put a bolt through it and chuck it up in a drill or lathe. Ideally you want something to count turns, building a counter is easy though, if you have an arduino or microcontroller board of your choice with a display you can whip up some code to do that easily. Or you can just guess by measuring the size and it will probably be close enough to work.