Unfortunately my Yuin Pk1's have stopped working once again after getting them repaired a few month's ago.
I thought I would post a picture of them completely disassembled for those who may be interested in seeing how ear buds work in general, or who specifically want to see how Yuin's PK1's are made.
The quality of the sound they produced was quite fantastic and the materials, although cheap, seemed to be put together well enough. But they just don't seem to hold up very well over time. My main hypotheses on why they break so often are; Cable insulation rubbing off and shorting themselves. The jack becoming damaged or warped. Or possibly the microscopic voice coil hairs break. Mostly I think its down too cabling issues, they should be fine for home use but if you are planning on moving around with them in your pocket I would expect them to break within a few month's.
Most of the components are glued together. I used a heat gun off of a soldering station to gently and evenly heat the glued areas before carefully removing the parts by pulling carefully with tweezers / gloved hands. (Lowest heat, keeping some distance, and remember don't keep any area under heat for too long!)
That's what YOU SHOULD do at least, or you'll end up with a melted front cap and speaker diaphragm like myself!
Enjoy! I'm going to try and reshape the front cap under heat and make a new diaphragm and reshape the voice coil later.