[R-390] Soldering Fine Wire

[Albert Solway]

To All Who Responded,

Thank you all who responded to my fine wire soldering problem. There
were many. I will attempt to explain the original problem again. Then my
adaptation of your suggestions which resulted in a successful repair.

I am sorry for not getting back sooner. I got an email from Greg
yesterday asking if I got any responses or any info on the aspirin
method question I posted.. This woke me up and I realized that if you
ask questions and get responses then you should share this info with
everybody.

I am in the process of restoring an SP-600-J-3. I was replacing one of
the BBODs in T1. A fine wire going form L52 to a terminal was broken.
There was not enough wire remaining to reach the terminal. I attempted
to splice the fine wire to length of solid lead wire. This was not
successful because the insulation on the fine wire inhibited soldering
of the wire. Attempts to melt the insulation with a soldering iron did
not work. It resulted in burning the wire and more wire being destroyed.
I tried the aspirin method but this resulted in a plastic like material
being deposited on the wire. The amount of wire remaining was sufficient
for one more attempt at a splice. Another failure would result in
replacing the entire T1 transformer. Availability would certainly be a
problem. This was when I decided to ask for help.

Several responded with variations of the same technique that were
specific to a particular problem. The main point that was made was that
only uncoated aspirin should be used. I used a COATED aspirin. This was
the cause of the plastic like coating that was deposited on the wire.
USE UNCOATED aspirin only.

My procedure for the above problem is only a variation of the suggested
techniques. The transformer fine wire used in L52 mentioned above was
approximately 40 AWG with a nonsolderable insulation. The remaining L52
lead was to short to reach the terminal that it was originally attached
to. A length of solid bare tinned wire about 0.020 in diameter was
attached to the terminal and soldered in place. The bare tinned wire was
used as a splice for the fine 40 AWG. Tweezers were used to wrap the
fine wire 4 turns around the bare wire. An uncoated aspirin was broken
in two. Using tweezers the aspirin was held under the wire to be
soldered. A soldering iron with solder applied to the tip was held in
contact with  the wire above the aspirin. The soldering iron was moved
back and forth two three times. The residue from the aspirin soldered
area was cleaned by scrapping lightly with an Xacto blade. The area was
cleaned with Isopropyl alcohol (IPA).  The aspirin soldering/cleaning
operation was repeated a second time. A light coating of solder flux
was then applied to the area and then resoldered. The result was a good
and well wetted solder joint.  I dissolved some baking soda in water and
rinsed the splice with this solution. The splice was then cleaned
thoroughly with IPA.

Bill Smith indicates that the acid in the aspirin may eventually attack
the wire. This a valid comment.  Rinsing  the splice with the baking
soda to neutralizes the acid. This is not my idea but one that I found
on the internet at the the following site. I downloaded their Wire Info
Software. Lots of good info on magnet wire including soldering of
nonsolderable fine wire insulation.

http://www.wiretron.com/magnet.html

BTW Google is a very effective search engine. There is all kinds of info
on magnet wire out there. The SP-600 T1 is now fully repaired and looks
good. Will finish the recapping and the other necessary repairs in a
month or so.

A Happy New Year to All.

Al VE2TAS