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Thread: Detached Pole Piece on JBL E140?

  1. #1
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    Detached Pole Piece on JBL E140?

    Hi.

    I bought a pair of JBL E140s on eBay. those are the ones with the big ceramic magnets. They were "broken" so I knew I would need to recone them. However, on one of them the center pole piece is no longer attached. It was wedged against the coil so tightly that I had to pull up the voice coil on the opposite side, bump the frame to move the pole piece to the opposite side, pull up on the newly freed side, and repeat until the voice coil was completely free.

    1) Can it be repaired?
    2) If so, how?

    Thanks!

  2. #2
    norealtalent
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    Contact LHS Member ATCAudio or call Tony at ATC Audio, 413-781-2327. ATC Audio is a fully authorized JBL repair shop and specialize in degauss repairs as well as recones and diaphragms. I highly recommend them for all factory authorized repairs.

  3. #3
    RIP 2011 Zilch's Avatar
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    Check more closely. It's most likely the magnet, with the pole piece attached, that is moving. You'll be able to see that it is out of concentricity with the steel front plate, if so.

    The one below likely needs a new magnet, factory service only, since a piece of the ferrite itself is fractured off.

    I have three of these now, sold "for reconing," from different eBay sellers.

    Frankly, I can't imagine how these are gettin' busted like this....

    My reconer says he can realign and reglue them, but only if virtually all of the magnet is intact. This one, "No WAY, dude...."
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    Senior Member Anthony L100's Avatar
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    Quote Originally Posted by Zilch
    Frankly, I can't imagine how these are gettin' busted like this....
    Yes Zilch, this is something i've also come accross in my search for some baskets to recone as 2235s. I can only guess that the "musical instrument" range of drivers are likely to get a tougher time generally, although you would imagine they would have to be dropped to do this sort of damage . In my search for suitable baskets from the "list" I reckon about 30% had shifted magnets. As quite a few members are looking out for these baskets at the moment it's probably good advice to establish there is no damage to the magnet structure before anything else, although some ebay sellers are not as honest as others.

  5. #5
    RIP 2011 Zilch's Avatar
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    Quote Originally Posted by Anthony L100
    As quite a few members are looking out for these baskets at the moment it's probably good advice to establish there is no damage to the magnet structure before anything else, although some ebay sellers are not as honest as others.
    And some of them are just plain ignorant, as well. They toss the frame into a box with no support or padding and call that "careful packing."

    It's easily seen that these are often mishandled in shipping, too. Just the right size and heft for tossing around the package sorting center, apparently.

    Carriers just laugh when they reject the damage claim as "inadequate packaging."

    I'm about done tryin' to acquire cores anywhere but local, where I can check them out and get them undamaged.

    If the voice coil is "frozen," chances are pretty good the magnet has shifted. Whether it's repairable or not requires disassembly for determination.

    Perhaps some of our factory service members have some alternative means of repairing these to share?

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    Quote Originally Posted by Zilch
    Check more closely. It's most likely the magnet, with the pole piece attached, that is moving. You'll be able to see that it is out of concentricity with the steel front plate, if so.
    Hi Zilch.

    You are correct! I just now checked and it is the magnet that is moving.

    So if this is the correct diagnosis, then what is the cure and how much will it cost?

    Thanks!

  7. #7
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    I successfully rebuilt a pair of Altec 411s that had loose magnets/pole pieces once, only because I couldn't bear to throw them away. It's a LOT of work, as I recall, it took me 2-3 days, not counting the repaint.
    As Zilch mentioned, you need to determine exactly what parts have come loose. In my case, one 411 had a floating pole, the other had both a loose pole and magnet. Since there was some rust on the poles, I decided to "go all the way" with a complete reassembly.

    To separate the rear plate from the magnet, I used an old, mild-steel butcher knife, with the sharp edge in the joint, a good whack from a wood mallet on the back of the blade did the trick. The same worked for magnet/front plate separation. (Use caution here, magnets can be easily ruined by a misplaced 'whack', also scribe-mark the magnet so you can reassemble with proper polarity). In my case, the front plate was screwed to the basket, so I left it in place.

    Inspection of the loose parts showed only a few dabs of adhesive residue, which may have been the cause of the problem. The assembly had not included what I would think to be a mandantory 'twist' of glued components to spread the adhesive.

    Complete cleanup of all surfaces is a given, I used sandpaper with a final wash in denatured alcohol. My first two glue attempts with various epoxies (which, by the labels should have been adequate) proved unsatisfactory. My third try using the old tried-and-true JB Weld held great.

    Naturally, properly centering all components is required, and is also the hardest part. I made individual "bushings" from PVC couplings and short pieces of EMT I modified to the correct size with the appropriate number of wraps of foil tape. A set of digital calipers is an asset here. Assembly works best from the back forward;
    1. Pole piece to rear plate.
    2. Rear plate to magnet.
    3. Magnet to front plate
    The final joint positioning is critical, as it ascertains the uniformity of the gap. The shims/bushing used here must be removable from the front (long enough to extend well past the front plate). With "live" magnets, clamping might not be needed, but I did it anyway.

    I'd label such a project as Extreme DIY, and not for the average hobbyist. If you find doing a refoam or recone any kind of challenge at all, don't even try this. Although mine worked out great, I'm not sure I'd ever do it again. If the 4" pole and gap hadn't luckily been the same dimensions as the items I found to fab the bushings from, I'd have been up the old creek.......you may be lucky to even find a reconer that will do it, and it won't likely be cheap.

  8. #8
    RIP 2011 Zilch's Avatar
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    Quote Originally Posted by Benkev
    So if this is the correct diagnosis, then what is the cure and how much will it cost?
    Contact your JBL Pro authorized transducer service center and/or JBL factory repair. Both can be located on the JBL Pro website.

    What you need is recone and magnet resetting. I'll be going through the factory for two of them next week, and will report back the cost for comparison.

    [Not gonna be cheap, I don't imagine. ]

    JBL factory service has always been good to me, but I doubt they'll consider THIS a warranty repair....

  9. #9
    Administrator Robh3606's Avatar
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    Are those 3 broken bolts in there??? How could you hit it that hard. dropped???

    Rob

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    Quote Originally Posted by Robh3606
    Are those 3 broken bolts in there??? How could you hit it that hard. dropped???
    'Last time I saw Zilch I think it was determined that even though there are matching holes in the magnet and basket, for some reason JBL only glues the magnets on - 'no bolts.

    John

  11. #11
    RIP 2011 Zilch's Avatar
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    Quote Originally Posted by Robh3606
    Are those 3 broken bolts in there??? How could you hit it that hard. dropped???
    No bolts, just holes, though there's tapped holes in the front plate that would line up with them, looks like. Some studs could be mounted there to grab the magnet and hold it in alignnment, yes. I guess JBL found they didn't need any attachment other than the glue. It grabs the front plate pretty hard magnetically, as well, requiring a tool pounded between them to separate as I've shown.

    Reconer says they've gotta be dropped to fracture like that. Maybe if a cabinet with one in it fell off the back of a truck or was bounced off a stage that might happen. I don't get it, unless the glue is giving up over time and rendering them more susceptible to damage. Note that it only held about 1/3 of the way around on the one above.

    It's also obvious from the way they pack them, the MI guys don't give a whit about taking very good care of these, either....

  12. #12
    Senior Member B&KMan's Avatar
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    tolerance pole and magnet.

    Quote Originally Posted by Zilch
    No bolts, just holes, though there's tapped holes in the front plate that would line up with them, looks like. Some studs could be mounted there to grab the magnet and hold it in alignnment, yes. I guess JBL found they didn't need any attachment other than the glue. It grabs the front plate pretty hard magnetically, as well, requiring a tool pounded between them to separate as I've shown.
    Hello,

    My comprehension on why JBL is only glued magnet is :

    the magnet is fragile material. the best perfect conctact to magnet and metal pole piece, the better than. Normally the metal pole contain "tool for alignment magnet and ideall never affect the magnet field. the glue is arround of the join magnet and pole piece. any strong bold risk to distord the pole and fracture the magnet... (and the bold in mu-metal and strong power is very costly).

    of course some time the magnet is badly gued and some time the 2 surfaces preparation is not good... more fragile, more distortion, and more risk to broken...

    anyway this is a speaker not a bowling ball.

    and if magnet is fractured or broken the driver is garbage... anyway probably the frame is distorded...

    sorry...

  13. #13
    Senior Member GordonW's Avatar
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    if anyone is planning to throw out any of these 15" frames with broken magnet, I might be willing to horse-trade for a few of them. Make good frames for building ersatz PR300s and/or PR15s (passive radiators). Have one frame now, need at least one more, though it's no big rush or anything...

    Regards,
    Gordon.
    This Is Gordon's Page: www.geocities.com/gordonwaters

  14. #14
    RIP 2011 Zilch's Avatar
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    Quote Originally Posted by GordonW
    if anyone is planning to throw out any of these 15" frames with broken magnet....
    Are you also saying they are not repairable?

    What are the limitations to salvaging these?

    Is my reconer correct, that unless the magnet is almost entirely intact, they cannot be reset?

  15. #15
    Senior Member GordonW's Avatar
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    Quote Originally Posted by Zilch
    Are you also saying they are not repairable?

    What are the limitations?

    Is my reconer correct, that unless the magnet is almost entirely intact, they cannot be reset?
    That's usually the case. If the magnet itself is broken, there's no way to get it re-aligned properly.

    If, OTOH, the magnet has come loose from the pole piece or top plate cleanly (ie, only the GLUE broke, leaving the magnet intact), then it's repairable... shim, and re-glue.

    Regards,
    Gordon.
    This Is Gordon's Page: www.geocities.com/gordonwaters

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