Yamaha NS-690 Frozen voice coil (Shifted Magnet)

hi-fi_EMT

New Member
I bought a pair of Yamaha NS-690 from Ebay for $460 shipped. The seller said they are "in good working condition".

I pulled them out of the boxes and checked them out. They look great so I proceeded to push on the woofers and one is frozen solid. I have communicated with the seller and they have asked what I think it will cost to replace the woofer.

I have searched for a replacement online and haven't found anything.

So what will it take to get a replacement woofer or have this one repaired? Where are some good places to look for parts?
 
Those are MkI's with the vented dustcap. The magnet has shifted and the voice coil my be salvagable as long as you did not push on the cone too hard. A good speaker repair shop may be able to repair it, but shipping may damage it furthur. Finding the correct replacement might take a while. Hopefully someone else will pop in with some value help for you.
Regards,
Jim
 
Those are MkI's with the vented dustcap. The magnet has shifted and the voice coil my be salvagable as long as you did not push on the cone too hard. A good speaker repair shop may be able to repair it, but shipping may damage it furthur. Finding the correct replacement might take a while. Hopefully someone else will pop in with some value help for you.
Regards,
Jim

I decided to cut the dust cap off and have a look you are correct it a shifted magnet. I have only gently pushed on them so I shouldn't have caused any further damage. Any links to repair tutorials?
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Find yourself a table vice clamp and carefully tighten down the magnet structure and "drive" the frame in order to open the gap.
Meanwhile position shims(card stock) to create an even space(gap).
While shims are in place remove the woofer from the clamp, use a very fast dry epoxy to secure the magnet to the basket, careful to not let the epoxy run into the voice coil area.
I let the epoxy get close to going off before I spot glue in multiple applications to avoid the epoxy running wild.
Easy Peazy;)
 
I've never experienced this before, but assuming that there was enough force to cause the magnet to shift during shipping, isn't there also a decent chance that the voice coil or VC former was damaged as well?
 
I've never experienced this before, but assuming that there was enough force to cause the magnet to shift during shipping, isn't there also a decent chance that the voice coil or VC former was damaged as well?

I would definitely say there is a chance.
 
I used to charge $100 a woofer plus shipping to fix these. I don't do it anymore because I have bigger fish to fry. However there is a guy on ebay that does. And he also shows pictures of his contraption to do it which would be easy enough to build yourself. Just look up "Yamaha woofer repair"
 
I tried it once with a pvc pipe, but the Yamaha woofer magnet is just too strong for the pipe and I wound up actually gluing one permanently broken. The PVC just gave out over the time that the epoxy cured. The wood one like the one on ebay appears to be significantly improved in strength.

I personally did it with a milling machine. And that process is described elsewhere and could probably be done with a large drill press.
 
I tried it once with a pvc pipe, but the Yamaha woofer magnet is just too strong for the pipe and I wound up actually gluing one permanently broken. The PVC just gave out over the time that the epoxy cured. The wood one like the one on ebay appears to be significantly improved in strength.

I personally did it with a milling machine. And that process is described elsewhere and could probably be done with a large drill press.

So if I'm understanding this correctly, you have to shift the magnet back into relative center with a vice or some kind of contraption and expoxy it to hold it in center?
 
Mine have never given me a problem, but it was suggested by a Yamaha guru that I should run a bead of epoxy around the magnet as a safeguard for the future, which I did.
Regards,
Jim
 
So if I'm understanding this correctly, you have to shift the magnet back into relative center with a vice or some kind of contraption and expoxy it to hold it in center?
Yes.

My method varied in that I actually removed the backing plate and magnet. I then cleaned the magnet and backing plate/pole surface, and the basket. I then epoxied them back together internally. But that can't be done easily without a mill or heavy duty drill press with such large magnets. So most people just center the magnet somehow and run the epoxy on the outside.
 
AFAIK, when woofers are built the baskets and magnets are glued together, and then the magnet is magnetized. In fact, that maybe how it's done for any speaker. I don't know.
 
I have a Yamaha midrange that is frozen solid, this might be the problem, I hope it is. So you had the dust cap off, turned the basket cone up, supported the basket off the drill base and pressed down on the pole piece?
 
So if I'm understanding this correctly, you have to shift the magnet back into relative center with a vice or some kind of contraption and expoxy it to hold it in center?
Yes.
The contraption seems a bit overkill and I'd dread pulling the magnet off the basket and damaging the voice coil.
Some might find building a contraption fun and involved but I just take the easy way with the vice clamp, shims and epoxy.
No mention of woofer resistance measurement yet?
 
Yes.
The contraption seems a bit overkill and I'd dread pulling the magnet off the basket and damaging the voice coil.
Some might find building a contraption fun and involved but I just take the easy way with the vice clamp, shims and epoxy.
No mention of woofer resistance measurement yet?

5 ohms
 
Yes.
The contraption seems a bit overkill and I'd dread pulling the magnet off the basket and damaging the voice coil.
Some might find building a contraption fun and involved but I just take the easy way with the vice clamp, shims and epoxy.
You would be relying on a bit of luck to get that right. The Yamaha magnet is extremly strong and the voicecoil gaps very small.
To build the 4-way adjustable jig would be quite easy. The voice coils are tougher than you'd think.
 
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