Rick Onanian wrote:
The transformer in my Tripp Lite "Internet750U" UPS appears to be dead.
120v goes into it (measured near where the power cord goes into it) but
nothing comes out the other side.

The sci.electronics.repair faq and http://sound.westhost.com/xfmr.htm
both lead me to believe I should check for a thermal fuse under the
insulating wrapping.

The FAQ says
"There may be a thermal fuse buried under the outer layers of the
transformer which may have blown. These can be replaced but locating one
may prove quite a challenge."

There's no visible bulges in the wrapping; do I just cut into it and try
to find the thing? I'm not terribly afraid to destroy it. If I can't
repair it, I'll want to hack the remains into a standalone inverter and
use a standalone charger with it (and maybe a bigger battery -- say, the
one in my RV).

Are there any other diagnostic tests I should try first?

If its a metal incased transformer you have to take the clam shell
shield off of it before you begin. if its a open type transformer, your
in business. First check the primary and secondary for continuity.
My guess is you will find the primary open. Measure at the leads
directly coming from the transformer. If the leads measure open, look
where the leads go into the transformer body. There will usually be a
plastic top and bottom of some molded variety. You need to cut away
this plastic carefully with a Xacto knife or such and follow the lead
wires down to the core. Look for a bulge in the core where the wires go
down. This will probably be where the thermal fuse is. If you found it,
very carefully pull it out of the transformer core with needle nose
pliers. Measure the thermal fuse for continuity. if its open, you can
either bypass it (not so safe way) or put in a new thermal fuse. If can
be a challenge to get a replacement thermal fuse back into the core.
then you have to replace the cut away plastic ends the best you can
and secure it. If your real lucky, the transformer core was not
damaged and it will work. If it works, check closely for excess heat
or smell.

Bob

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