# Technical Question - 'spot' On F300 Coil



## Who. Me? (Jan 12, 2007)

While stripping down the Tissonic to sort the crystal, I gave it a once-over, and couldn't miss a bright spot on one of the coils...










(Apologies for the image quality, my compact's Macro setting isn't designed for this sort of close-up.)

It's running and humming fine, so should I be worried?

To the 'untrained eye' it looks like the insulation is damaged in one spot (it glints sliver when tilted against the light).

Any opinions from those who've dealt with enough of these to know a problem when they see it?

If the insulation is damaged, should I do anything to protect the spot from oxidisation?

Cheers

Andy


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## pg tips (May 16, 2003)

loks like someone might have dropped a screwdriver and it hit the coil, lucky it didn't break the winding.

IMHO if it ain't broke...


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## Silver Hawk (Dec 2, 2003)

Andy,

Are you sure this is not just a small air bubble that dried on the surface of the hot shellac when the coil was first made? I've certainly seen this type of superficial imperfection in other coils when viewed under a microscope.

If it was caused by any physical damage, I'm sure it would have damaged the windings. If the coil is working, I'd leave it well alone. If you really want to seal it, just dab a spot of varnish on it.

Cheers

Paul


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## jasonm (Nov 22, 2003)

Silver Hawk said:


> Andy,
> 
> Are you sure this is not just a small air bubble that dried on the surface of the hot shellac when the coil was first made? I've certainly seen this type of superficial imperfection in other coils when viewed under a microscope.
> 
> ...


What colour is your shade of varnish Paul?


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## Silver Hawk (Dec 2, 2003)

jasonm said:


> What colour is your shade of varnish Paul?


*You need to ask me that? I live in Brighton.*


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## mel (Dec 6, 2006)

If you're going to spot varnish onto the bare bit, practice first using an artist's brush, as fine as you can handle. Too much varnish running into other bits won't do the item any good









Whilst I've never tackled this on a watch, I have done it to coil windings in sub mini radios. You just want enough to cover the bare bit and no more.







(yeah I know, don't we all?)


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## Who. Me? (Jan 12, 2007)

Thanks for the advice everyone.

I'd wondered if a tiny spot of wax would seal it.

Clear nail-varnish makes more sense, of course.

Don't know whether it is damaged or just a manufacturing imperfection, but I will seal it anyhow, if only to stop me from checking that it's still working.

And I will be sure to take the battery out before doing so.

Cheers

Andy


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## KEITHT (Dec 2, 2007)

Its not uncommon to find blemishes/spots on the coils.

Some i would suspect are manufacturing defects, others telltale signs of clumsy repairs.

Providing the windings aren't damaged, in which case it wouldn't work anyway so i wouldn't worry about it.

I haven't seen much evidence of any coil corrosion etc on affected coils before.

If you fiddle with its likely to all go pearshaped.


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