Re: NST Failure... What happens?

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "davep by way of Terry Fritz <twftesla-at-qwest-dot-net>" <davep-at-quik-dot-com>

Tesla list wrote:

> Original poster: "ROBERT L BOZARTH JR. by way of Terry Fritz
><twftesla-at-qwest-dot-net>" <jbdetails-at-prodigy-dot-net>
 
>     My 15K 30ma NST stopped working suddenly, about 10 seconds after
> my "first light". First I was very excited.... Then really bummed.
> So I grabbed my multimeter and checked the secondary resistance of
> the NST. I assumed that when a NST goes that it would be in the
> secondary windings.

	Sometimes, but:

> However, I got a reading that seemed normal, so I checked the primary
> side. Open circuit on the primary!
> How? Why?

	Several possible reasons:

	Many/all common devices have an embedded 'fuse' (not
	necessarily a 'usual fuse'.  Commonly will open,
	permanently, on exceeding input current OR over temperature.

	If that's the issue, and IF it an be found, it an
	be replaced (or bypassed).  Bypassing protective components
	is iffy... 
	
	Why did it open?  It saw too much current, or a winding
	over temp.  Or it THOUGHT it did (possibly defective
	protection.

	Possibly weak solder joint in there somewhere.

> I depotted the now non functioning transformer in hopes to find out
> exactly what happened. It seems that the input to the primaries
> innermost winding was broken off.

	Sounds like a good find.
	Broken or melted (if easy to tell.)?
	Curious that it should have broken, if potted...

> It would have been an easy fix but I damaged the "finer than hair"
> secondary wires. I'm still going to try, but I could sure use some
> pointers....

	Loss of 'a few' turns of secondary is not super important.
	Proceed delicately...

	best
	dwp