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quartz watch coil repair

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This came to me recently as part of a "Merry Christmas, I will fix your watch for free" box of watches.  This thing is "Walmart" class cheap quartz watch, but the guy wanted it fixed to some level.

Clearly, past battery replacements took their toll on the watch and damaged the coil.  This is a Ronda movement and I would have replaced it outright except I could not find it anywhere.  So I decided to apply my uber electrical engineering skills along with my amateur watchmaking abilities.

You can see the broken wire in the picture and I have drawn in the desired connection in blue.  I unwrapped the coil one turn from both broken ends.  Had plenty of material to work with.  Then I soldered them together--trick with this fine wire.

Not shown in these pictures, is the repair I did to the negative-contact terminal.  It was broken due to battery acid.  I soldered a 30 gauge wire to the terminal and flattened it out on a bench block with a brass hammer.

Not sure where to go with the missing part of the case, but I am going to look around for something.

The whole point of this exercise is to learn and improve my skills.

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14 minutes ago, LittleWatchShop said:

Never heard of such.  Something to investigate. Prolly easier than soldering!

I think it be better if you solder the wire and don't think about the circuit fixing stuff? Typically when somebody slips you can end up with multiple of breaks. If it's just one break that's better but typically it's not. Some of the circuit fixing compound is basically a conductive paint. So the objection that I had if it was a cut with multiple of breaks painting it with the solution would cause multiple of shorted coil turns conceivably. So at some technical level this would be a bad thing to do.

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28 minutes ago, Nucejoe said:

I didn't get that, how did you fix this, did you solder?   When I try it, the  fine wire literaly burns.

This is correct, you have to be quick.  First, you have to unwind essentially two loops which gives you a long pigtail to work with.  The solder/heat will melt and break some of the wire and it falls off leaving what is remaining soldered together.  In retrospect, I would have dialed down the temperature of my iron and also used my finest tip (which did not do this time).

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3 hours ago, Nucejoe said:

solder?   When I try it, the  fine wire literaly burns.

If you look at some of the quartz watches you'll find that there soldered from the factory. So obviously it can be done but you would have to be careful what the temperature as that is really tiny wire. Then I doubt did you really have to clean the insulation off it's probably designed to burn off on that soldered it be an interesting experiment to try and see if that's true though.

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 Back in 90s when quartz movements were popular , there were jobbers in Iran who rewound watch coils all day in a funny looking home made rig that consist of an electric motor attached to some hand made adaptors on which they mounted these to rewind. I never watched how it was done, they did solder terminals  as well, you could get a rewound coil for a dollar plus exchange.   

  @AliMoloodian a WRT member used to rewind them for his own use. He doesn't understand much English so I'll ask him to show pix of the gear. 


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2 hours ago, Nucejoe said:

Back in 90s when quartz movements were popular , there were jobbers in Iran who rewound watch coils all day in a funny looking home made rig that consist of an electric motor attached to some hand made adaptors on which they mounted these to rewind. I

Interesting skill set to have today? There's at least two people out there that I know of that are rewinding coils like in the really expensive quartz watches where the coils are basically impossible to get and they're not necessarily a scratch type repair where you can paint that they basically have to be replaced but can't because don't exist. Then there's somebody out there rewinding the coils for tuning fork watches of course the same thing where there damaged internally somehow so it's still an interesting skill to have today because there are watches were the coils need to be replaced and they cannot be fixed with stuff like this unfortunately

4 hours ago, Plato said:

, some of the surrounding wires shorted out but not too many to matter.

It's a shame we didn't have a PhD electrical engineer around when you need one?

The liquid paint Conductive type stuff  around ever since the coils began. But just because you short out a few turns of the coil and seems to work the resistance seems good does it really have an effect or not? Does the current consumption go up a little bit is there a power loss or is it just one of those weird obsessions that somebody gets concerned about that worries about where every single electron goes?.

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22 minutes ago, JohnR725 said:

Does the current consumption go up a little bit is there a power loss or is it just one of those weird obsessions that somebody gets concerned about that worries about where every single electron goes?.

The pictures I posted were of coils for the chronograph subdials... it might matter more for the continually revolving seconds hand. I should have mentioned that, good spot @JohnR725. I think it was a drop from 1k7 to 1k5 ohms, so better than scrapping the movement if parts are not available (or too expensive for YOUR watch). 

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I would say that the impact of reducing coil resistance in these ranges is insignificant.  That is my SWAG anyway.  The model for the coil includes inductance, resistance, and capacitance.  All of them change as a result of shorting some turns.  Since the coil is functioning as an electromagnet (versus a resonator), I cannot imagine it making much difference.  It will likely increase current but that means changing the battery a month or two earlier perhaps.

The actual answer requires carefully modeling the driver circuit, the load (the stepper rotor and train wheels), and the coil, and then simulating.

Short a few turns and move on!

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4 minutes ago, LittleWatchShop said:

I cannot imagine it making much difference.

The reality is scratch the coil and something you can't replace or for other reasons putting this nifty stuff on fixing the problem make the watch school way is an easy fix. Although the last one we did it work didn't last for a long and it came back.

Depending upon a whole bunch of factors and other coil types shorting even one turn on some applications would have very interesting effects. This is why needed somebody obsessed with electrons as to the practical world probably it doesn't matter. But at some obsessed level it probably does matter.

Mike if you have one of those modern witschi timing machines for quartz watches ill tell you like how wide the motor drive impulses are. There with expands as the circuit perceives there's a load with the circuit perceives there's a load because part of the coil is shorted out for instance?

But this stuff is existed as I said from the beginning of when coils existed in watches.

Before this conductive epoxy existed for re-gluing the little tiny wire leads on LED displays. Yes that's a different subject but they really did make a kit silver epoxy and about 6 inches a super Tiny gold wire just in case you needed a replacement piece. Yes it was really a fun thing to do under a microscope and well I guess if you can get a segment back partially it was better than no segmented all.


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 Accrding to our friend  Alimoloodian , coil's resistance is the only factor that counts, how nice the wire is arrayed wouldn't matter. 

There are also coils wound with two wires somiultaneously for double circuits I suppose. 

Low speed motors are recommended, its only a matter of making an adaptor mounted on the motor shaft.

I insisted he shows the aparatus he made on the forum. 

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  • 2 months later...
  • 4 weeks later...

Very useful stuff. Let me add my experience with watch coils.

I have an invicta watch with Ronda 5030d which I purchased some years back through Amazon.

Last time I changed the battery, I used an unbranded chinese battery from ebay(never again) which spillover and tarnished everything, and after a complete clean-up to all gears, I noticed that two of the smaller coils where busted. Don't remember if it was me in the past or if was already damaged. I don't recall the chronograph every properly working. The other two I also damaged as I had to remove the controller board multiple times until I figured a bad connection between the battery pin and the circuit board and finally properly soldering it, and one of the times the screwdriver slipped and the other time the coil circuit board moved with too much screw torque.

By the way, I also figured out that after cleaning all the isolation (as was full of battery residuum) from the board the quartz oscillator was not working, and correspondingly not coil pulses could be seen (on the oscilloscope). I tested it with some other quartz but still not working. Finally I soldered back the original quartz and worked at times (I could see the 32Khz on the oscilloscope), and only started properly working when I covered the short tracks between the micro-controller and the small quartz with the green UV resin. Maybe there is some capacitance effect made by the tracks and the isolator that is not there/is different if you remove all this isolation stuff. Colpitts oscillators are very sensitive to the capacitances.  

Anyway after board fixed and watch cleaned was time to focus on the coils. I managed to repair the two I damaged by micro-soldering it, but is not easy as we cannot pull the thin wires with a clamp as they are so fragile. I broke the wires in the coils I could not repair like that. I learned the hard way in the other coils and I managed to put the wire in place with a sharpen wood stick.

If using soldering iron in the microscope you also need to be very careful with it. If it is hot and you happen to accidentally touch the coil, immediately the solder sticks and you get a short of several laps. One of the unrepairable coils I first managed to repair but I touched the coil on the side with the soldering iron tip and a blob of solder made it from 2K ohms to 500 ohms. Then attempting to remove the blob I further damaged the coil.

I also have the conductor glue but I decided the soldering as I didnt had to wait it to dry and I am kind of used to the micro soldering and have a soldering microscope. Unfortunately there was a learning curve.

For the other two I don't see where the coil starts to pull the string. I am out of ideas and these coils are not sold online to the common folks.

3621.055.RK and 3621.054.RK

I could wind them from scratch but I believe they use 0,012mm wire (AWG 56) which I don't see available to sell online. For the 2kohm thy have this represents 13 meters of wire.


I have 0,076mm wire but even if I could add the 13 meter in the coil volume/space, which I doubt, would correspond to 50 ohms resistor which would drive much more current from the battery (in the order of mA instead of uA).

I could add a 1,8K ohm SMD resistor in series and get roughly the same current but I need to check if this would still drive the step motor. At this moment I don't want to mess the coils yet by removing existing wire, as would be very difficult to unwind. If I could find the ends I could as well solder it. 🙂

In the end is a lot of work because the AWG wire is not readily available and these special coils are not provided by the retailers except on B2B, and from China these models of coils are not available, only complete movements. 🙂 A new movement from china is probably the best option but would not be as fun.

The watch is working now but missing the 30 minute and 12 hours count for the chronograph part. 🙂

Any advice appreciated, and I hope my experiences may help others.





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3 hours ago, jorgemef said:

I could wind them from scratch but

If you are adventurous you could unwrap a coil from a donor movement and use it to rewind the coil of the Ronda.  That seems like a labor of love, or an experiment just to prove that it can be done.  Alternatively, buy a new movement  for $50 and be done.

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6 hours ago, jorgemef said:

I could wind them from scratch but I believe they use 0,012mm wire (AWG 56) which I don't see available to sell online.

the first link I have is the parts listing for your movement. It lists all the coils found in this watch clicking on each one you find the cross reference to other watches. That will expand your search on eBay for a replacement course coil as is probably the only way or originally get one.


basically if you take the parts found at the site above a go to the links that I have below who knows that might be available? Usually after not available oil say discontinued out of stock or something so it looks like the red one is available


blue coil is a perfect example of it's not available


then the other coil which is probably just the main coil that's also not available one out of three not too bad



then I don't see a price but here's a company that has that wire



then there's this website? Yes I know it's wrong coil but he is a really big spool wire if you go to the homepage and look at his recent projects he's apparently been winding lots of portals you can see what he would charge or if he tells you where he got his wire from.



oh then there is the other option is not as much fun not as much challenge but have you tried looking for this movement on eBay? Looks like they can be purchased brand-new for less than $60 each. I see several sellers currently claimed they have them. There may be a height difference between your movement but who cares you could steal the coils and the circuit while you're there. 




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