I finally figured out how to stitch a few videos together on my phone and add a graphic. Better for multiple step repairs. I know...right?
This is a typical shifted top plate of 1980s and beyond JBL ferrite magnet speakers. Customer sent me his recone kit parts after discovering the voice coil was clamped in place by the shifted top plate/gap. I used to do these with live magnets, but believe me, it's much safer to discharge the magnet before separating the top plate for realignment. Fun stuff! The motor parts are bonded together with epoxy. A few things can happen that will result is a shifted top plate or back plate/pole piece. If the epoxy is not mixed with the right ratio of catalyst/hardener, sometimes the epoxy can fail because it's too soft. I've seen this before. The epoxy is kind of soft and gooey, and a drop or physical jolt will make the assembly shift from the magnetism in the voice coil gap. Another problem that can arise, is excess moisture causing some corrosion to develop between the steel top plate or the cast iron back plate casting. The beauty of modern adhesives...namely elastomer modified cyanocrylate...the bond is better than epoxy and nearly impossible to separate after reassembly. Often times the magnet will break before the bond does.
AlNiCo motors can shift as well, but it takes a catastrophic amount of force for that to happen. The frame screws go through the top plate and into the wall of the cast iron housing to hold it all together. The AlNiCo slug is bonded to the back of the cast iron pot assembly as well the pole piece...and the AlNiCo magnet is actually part of the pole piece since it sits directly under, and is bonded to the center pole piece plate... and is also held in place by the force of the magnet. The epoxy used in this assembly is a super strong aerospace grade material.
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4 мар 2024
