Kelly,

It highly likely that there's an internal short in the
winding. To locate the exact spot is really pain-staking. If
your transformer is not varnished, you may unwind the
suspected winding turn by turn (or several turns at a time)
with the inductance checked. See when the inductance comes
back to normal. Normal means L=AL x N^2 (AL can be find in
the core supplier catalog). When the approximate location is
found, the exact coating fault can be located by
electrolytic method.  That is, immerse the wire segment into
salt water (as electrolyte). Supply low voltage to the wire
as anode and another metal piece as cathode. You will see
bubble coming out from the faulty spot.

K.K. Chin
Artesyn Technologies
www.artesyn.com



From: Kelly Schauf <[log in to unmask]> AT NetMail on
      08/19/98 10:27 AM EDT

To:   [log in to unmask] AT NetMail@ccmail2
cc:    (bcc: KK Chin)
Subject:  [TN] PC board mount transformer problem





To the forum:

     Currently, I am testing a printed-circuit-board-mount
transformer. There is one primary winding and three
secondary windings. There are two powdered-iron 'E' cores
that are epoxied together around the bobbin to provide the
core for the transformer.

I have a problem where the inductance and the Q of the
primary coil drop way below normal past 1500 Hz with a
signal of 100millivolts AC applied. I suspect that there is
a shorted turn of wire that may be causing this.

Generally, there is maybe 1000+ turns of wire on the
transformer, and the chances of finding a marginal
short-circuit with merely a microscope and the eyes is a
'needle-in-a-haystack' type of chance. Is there some method
that would incorporate an electrical signal that would
enable me to find a short-circuit in the primary winding?

Any and all ideas are welcome. Questions are also welcome.

Regards,

Kelly Schauf

SIGNATURE:
For my webpage containing links to Quality and Electrical
Engineering as well as Failure Analysis (Electronic,
primarily) and ISO9000, go to http://web.gmtcom.com/~k3jsch


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