I am in the middle of repairing a Proficient S12 subwoofer. There are a number of blown transistors and resistors in the power amplifier that needs replacing.

Then I ran into a snag. The amplifier was intermittently drawing too much current and tripping the circuit breaker. (I have a DIY electronic circuit breaker which I use for such situations.) Then I found that the toroidal power transformer itself was sometimes pulling more than 1 A even with the circuit board unplugged. That's 120 W! Suspect: a short in the transformer.





After taking the plastic wrap off, sure enough, I can see charred windings.
Now I have my work cut out for me. If luck is on my side, I wouldn't have to unwind the entire transformer. I will keep you posted on this repair.

 

Maybe you will be able to apply a replacement lacquer in situ. That would be nice…

 

Forty turns off the pair of secondary windings and I've reached the trouble spot. I am thinking of using the wife's nail polish to coat the wire. Any other suggestions?

 

Forty turns off the pair of secondary windings and I've reached the trouble spot. I am thinking of using the wife's nail polish to coat the wire. Any other suggestions?

That should work but the only thing is to make sure it is very dry before rewinding because you can push through it mechanically if it’s not. If she as UV cured polish, that’s even better...

 

Even though the enamel is certainly discolored from what could be excessive heat, I could not find any exposed copper, both visually and with a continuity check. The windings on the lower layer appear normal, hence the heat is not coming from underneath the exposed windings.

I think I need to go back and check with high resistance test.

Edit: Ok, I found one weak spot. There must be another spot but I cannot locate it.

 

Even though the enamel is certainly discolored from what could be excessive heat, I could not find any exposed copper, both visually and with a continuity check. The windings on the lower layer appear normal, hence the heat is not coming from underneath the exposed windings.

I think I need to go back and check with high resistance test.

Edit: Ok, I found one weak spot. There must be another spot but I cannot locate it.

Sounds like one of those problems. I wonder if your repair will lead to cascading troubles.

 

The windings are going back on the transformer.
I have coated the bad spots with nail polish. Then I am applying Kapton tape in between layers and wires.

 

When I unwound the windings, I kept all the bends intact, thinking that I will replace the windings the same way as original. After winding two turns, I quickly realized that that is not going to happen.

Hence, I straightened all the bends and will just lay the wires as they go.