The second hand market is filled with great audio gear. For example, last week I bought a high end Yamaha amplifier (DSP-A1, 5x 115W RMS) for only 18€ on eBay and just had to clean the volume potentiometer (I used this technique)!
This time I purchased the exceptional B&W DM-602 S3 speakers (on eBay as well) for 91€ with two defective tweeters. In good condition, these speakers sell for 200 to 300€ and replacement tweeters cost 75€ plus shipping so I guessed 91€ was a regular deal at worse.
First thing I did when I got my hands on them was to detach the tweeters: remove the woofer, the tweeter can be removed from the inside by twisting it. As expected, both tweeters were burnt and read 'open circuit' when measuring the resistance at the terminals.
This is a very common issue which occurs on B&W DM600 S3, DM601 S3, DM602 S3, DM602.5 S3, DM603 S3, DM604 S3 (as they all use the same tweeters and probably many others using the same technology) when pushing these tweeters too far (too much power, having the amplifier clipping...) and the coil simply burns as a fuse would.
When the coil burns, a repair usually either involves replacing the whole tweeter (with the magnet and everything for about 75€/piece) or only the voice coil (10€ for two but is is way trickier).
If you open the tweeter, you will see the wire running from the terminal, looping around the dome and back to the terminal. The coiled part is bathing in a oily fluid meant to cool it down leaving the rest of the wire more exposed to overheating and more likely to burn.
This is a good news because repairing the coil would be close to impossible and the rest of the wire is exposed and therefore accessible for soldering.
Finding the burnt part of the wire is difficult and the worst of all is that with both my tweeters the spot where it ruptured was located just next to the coil, glued to the dome. With a sharp blade, I was able to detach a small portion of the coil to solder it back to the wire coming from the connector (use a very thin iron). That's was it, it worked as new!
The images below might not be very clear so here is what you should see: the front wire is reattached to the coil with a tiny tiny solder joint.
End note: I won't even keep these speakers... I love my old Marantz speakers too much to replace them! They come straight out of the 70's and they sound like a turntable would. Best of it all: they cost me about 10€ at a flea market 15 years ago ;-)