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Re: repair



Tesla List wrote:
> 
> Subscriber: gweaver-at-earthlink-dot-net Sun Jan 26 13:31:37 1997
> Date: Sun, 26 Jan 1997 10:08:01 -0800
> From: Gary Weaver <gweaver-at-earthlink-dot-net>
> To: tesla-at-pupman-dot-com
> Subject: repair
> 
> I have noticed many posts saying shorted neon transformers could be revived
> by removing the tar which has carbon tracks from an arc.
> 
> I have 4 bad neons I would like to try and bring back to life.  Before I try
> this I have some questions.
> 
> How are the high voltage insulators attached to the secondary coil?  Is there
> any chance of breaking the wire connection to the windings?
> 

High voltage wire is used internally to connect from the secondary
windings to the insulators. Remove all the nuts on bolt going through
the insulator. On many transformers, the insulators are actually
"twist-locked" into place throught the metal case, and held in place by
the hardenned tar. If you want to "save" the insulators, you'll need to
either melt or dissolve the tar. A somewhat messy, but easy way is to
open the case along the weld or folded metal using a chisel or large
screwdriver. Once you've exposed the tar on both sides, soak it in
kerosene or paint thinner in a 5 gallon plastic pail for a few days.

> Someone suggested putting the transformer in the freeze to make the tar
> brittle.  Then take a hammer and beat it to death to get the tar off.  Whats
> the chance of smashing the windings and permanently damangeing it beyond
> repair?  If the case is removed what holds the high voltage insulators in
> place?

Neons basically look the same inside with a primary winding in the
center and the two halves of the HV windings on either side. Don't try
to take big chunks off - chip smaller pieces off until you can tell
where the windings start. By removing the bigger chunks, you can speed
the soaking time in solvent.

> 
> Someone suggested putting the transformer in a solvent for several weeks to
> disolve the tar.  Kerosene or paint thinner will probably work. What type of
> solvents will work?  What type of solvents will not work? 

Anything that's not explosive, corrosive, or overly aggressive will work
Kerosene, turpentine, mineral spirits are all fine. Anything that will
dissolve tar will work just fine. However, stay away from gasoline,
acetone, naptha, or benzine - they're too dangerous, aggresive,  or
explosive.

 I know Acetone
> will remove everything except the metal and leave only bare uninsulated wire.
> Will the solvent soak into the primary and secondary windings and cause any
> problems?  Has anyone tried this?  How long did it take?  What solvent did
> you use?
> 
> I have been told that tar melts at about 400 degrees F.  The local motor
> rewind shop told me they cure the new motor windings in an oven at about 500
> degrees F for several hours.  Transformers that have to be cured are cured in
> an oven also. It should be possible to heat a transformer in an oven and melt
> off the tar.  Has anyone tried this?
> 
> Could most of the tar could be removed in an oven. Then the rest disolved
> with a solvent.  What do you think?
> 
> If I can't fix it, I can fix it so it can't be fixed.
> 
> Gary Weaver

I "cooked" one in a Weber grill last summer (my wife refused my request
to let me bake one in her oven!). Molten tar stinks terribly, and can
burn your skin like napalm - "cooking" should only be attempted
outdoors. After trying it once, I'd opt for the freeze-and-chip or
dissolve-and-conquer methods! Also, only some transformers can be
rescued. If internal arcing has carbonized part of the secondary winding
itself, then that secondary winding cannot be saved. Since many times
only one-half of these go bad, it's often possible to save "good"
secondaries from two transformers of the same type to assemble one good
transformer from two defectives.

Safe cookin', freezing, or dissolving to ya!

-- Bert --