Stuck Voice coil magnet shift..

Options
crassmage
crassmage Posts: 32
in Troubleshooting
This may have been discussed ad nauseum but I may need some help.
Here goes:

I am an avid Polk lover. My first Decent speakers are/were some old monitor 7s. Nothing has knocked them off my main system. So I finally stopped trying to upgrade as it wasn't happening(Polk monitor 7s are amazing). Made wife happy anyways...
Fast forward to yesterday I was at a thrift shop and son finds a pair of monitor 10a. I HAD TO! Didn't bother to even check but when I got them home 3 of the 4 drivers were seized up. Tried the PVC pipe method for a long time this evening and I'm about to give up. Is there anyone who fixes these around here? First post. Thanks for ANY help!
0 0
· Share on FacebookShare on Twitter
«1

Comments

  • lawdogg
    lawdogg Posts: 450
    Options
    I am more than happy to help. It sounds like you already have a re-centering tool going, so maybe I can offer some advice about how to use it? Are they just failing to re-center, or do they keep shifting while they are in the tool, or some other issue?
    <3 my 3.1TLs

    I will fix your shifted magnets for free. :)
    · Share on FacebookShare on Twitter
  • crassmage
    crassmage Posts: 32
    Options
    Wow thanks for the warm welcome! I am in Minnesota. Not much around here for vintage audio repair.
    My issue is yes I made the rig albeit my pipes are 2 inch cuts via the nice kid at the hardware store. I'm handy enough. But I just can't get it to free up the speaker. I have 2 I am trying with but neither ever gets to the point to where it moves freely..
    Thanks again
    · Share on FacebookShare on Twitter
  • delkal
    delkal Posts: 764
    Options
    Are you sure the adhesive broke and the magnets shifted (can be fixed)? Or did someone cook the voice coils (can not be fixed).

    When you take off the dustcaps is the coil centered in the magnet?
    · Share on FacebookShare on Twitter
  • crassmage
    crassmage Posts: 32
    Options
    I have the dustcap off one. Centered? It's still in there. I'm not sure if cooked or what to be honest. Would a picture help? Just won't move is all. I will give it another go today. Sound/music still comes out of driver but obviously not the sound I need..thanks!
    · Share on FacebookShare on Twitter
  • FestYboy
    FestYboy Posts: 3,861
    Options
    Yes on the pictures
    · Share on FacebookShare on Twitter
  • crassmage
    crassmage Posts: 32
    Options
    Any pic in particular that could aid in finding out? Voice coil, magnets,etc. You guys are great!
    · Share on FacebookShare on Twitter
  • pitdogg2
    pitdogg2 Posts: 24,574
    edited September 2019
    Options
    all
    including your jig may be of help
    · Share on FacebookShare on Twitter
  • crassmage
    crassmage Posts: 32
    Options
    Will do!
    · Share on FacebookShare on Twitter
  • crassmage
    crassmage Posts: 32
    Options

    8nrhtnrpqupm.jpg
    175kmt059p4l.jpg
    1sq427zyu9cf.jpg
    caujc1rlkfjl.jpg
    1kajtpvt2o63.jpg
    ca2svmmu9zhi.jpg
    d2lu0h6y84tz.jpg
    · Share on FacebookShare on Twitter
  • lawdogg
    lawdogg Posts: 450
    edited September 2019
    Options
    Alright I see what's going on. That PVC jig won't work - let me explain. You may be able to make a cut in it and get it to work, or you might need to get another size pipe (I forget what size works ... there are actually two different sized magnets, if everyone didn't already know that). Why do you need to cut it?

    The way the jig works is that is clamps the magnet, and the screws move the frame relative to the magnet / pole piece assembly ! So you need a way to clamp the magnet and hold it in place relative to the frame. To do this, cut a section out of the PVC pipe, and use a hose clamp.

    Here's what your jig should look like:

    cfox1bjvyqlp.jpg

    Before you put the driver into the jig, make sure the pole piece and magnet are securely fastened to each other! I always epoxy them together and let it cure BEFORE the driver goes into the jig.

    zv72jko1t7ck.jpg

    Once the driver is in the jig, and the hose clamp is tightened to hold the magnet in place, the screws will move the frame relative to the pole piece.

    cp4oxprwasml.jpg

    Now you need to gently move the frame so the voice coil is centered perfectly around the pole piece. I took some pics to help explain:

    Bad ... Bad ...

    a5f3ptjc614n.jpg

    6zqf5edzrxkw.jpg

    Good!

    i6734de6es2g.jpg

    Here's how to visualize the voice coil - if the voice coil is the electrical tape, here's how you need to center it.

    Here's what happens when the "magnet" shifts, the voice coil gets clamped by the pole piece and can't move.

    2o0upds3qzj6.jpg

    If you screw the frame over too far in the other direction, it'll snap the other way.

    l0cchcbps5vy.jpg

    So use patience and finesse, gently turn the screws to get it exactly centered, concentric in the middle so that the voice coil can move freely.

    irtshqpvmnix.jpg

    A hard lesson I've learned - sometimes once it's re-centered, the moment you loosen screws to remove it, it'll snap back into a shifted position. Dang! So what I do is apply the magnet-to-frame epoxy BEFORE putting the whole assembly in the jig. Once it's centered, I leave it in the jig until the epoxy has cured, and then can remove the jig without fear of re-shifting.

    Cheers and happy re-centering!
    <3 my 3.1TLs

    I will fix your shifted magnets for free. :)
    · Share on FacebookShare on Twitter
  • lawdogg
    lawdogg Posts: 450
    Options
    I'll add that your voice coil & former do look a little ragged. You need to make sure your voice coil is good (does it measure OK?) and make sure that the voice coil former is smooth and round. Otherwise, since the tolerances are so tight, it has a chance of not being able to center properly without scraping as it moves up and down. Been there done that! :'(
    <3 my 3.1TLs

    I will fix your shifted magnets for free. :)
    · Share on FacebookShare on Twitter
  • crassmage
    crassmage Posts: 32
    Options
    Thank you so much. I have some time today. Hope to find success. How do I measure the VC? Ohms? Thanks again for taking the time
    · Share on FacebookShare on Twitter
  • lawdogg
    lawdogg Posts: 450
    Options
    Yes ohm it out to make sure it's not open.
    <3 my 3.1TLs

    I will fix your shifted magnets for free. :)
    · Share on FacebookShare on Twitter
  • crassmage
    crassmage Posts: 32
    Options
    So basically we want a reading i.e. 1 and not Infinity. One on _ post one on + post.
    Correct?
    · Share on FacebookShare on Twitter
  • FestYboy
    FestYboy Posts: 3,861
    Options
    No, 1 and infinity are interchangeable on multi meters. So don't trust that.

    If the coil is good, and you have one lead on each speaker post, you should read all least 3.4 ohms ( depending on the driver tested as most don't carry a nominal impedance less than 4 ohms. A DC resistance check will always read lower than nominal impedance spec.)
    · Share on FacebookShare on Twitter
  • crassmage
    crassmage Posts: 32
    Options
    Ok. Was using 1 as a number is all. They checked out ok. The 2 I have out anyways. Gonna go for it. Thanks for the input!
    · Share on FacebookShare on Twitter
  • crassmage
    crassmage Posts: 32
    Options
    So I made a similar rig. I epoxied the cap and magnet. Dried. Put in PVC pipe. Then measured where the pole plate would sit within the pipe. Put screw in there to keep it from budging. The PVC held the magnet in place. Put glue on magnet(top) to be stuck to basket plate Then put basket in and had screws to adjust that. Voila! Once it moved free I hooked it up to a tone generator and tested in the 50-60 range and adjusted screw until silent. Now will wait for glue to dry. Promising at least. Thanks for all the help everyone.
    · Share on FacebookShare on Twitter
  • crassmage
    crassmage Posts: 32
    Options
    So checked one last time and did a subtle bass test at low volume to see. Tested good. No buzz. But a little flicker and my amp blew a couple fuses. Replaced them. Still blow. Coincidence or something I could have done with this speaker? Doubtful but I'm new to all this.
    Thanks...
    · Share on FacebookShare on Twitter
  • FestYboy
    FestYboy Posts: 3,861
    Options
    In my experience, test tones in the 7-11 Hz range will show any real issues. 50-60 can still hide a rub, especially at low volume/excursion.
    · Share on FacebookShare on Twitter
  • crassmage
    crassmage Posts: 32
    Options
    I will test that thanks!
    · Share on FacebookShare on Twitter
  • lawdogg
    lawdogg Posts: 450
    Options
    You mean the fuse in the speakers or in the amp?
    <3 my 3.1TLs

    I will fix your shifted magnets for free. :)
    · Share on FacebookShare on Twitter
  • crassmage
    crassmage Posts: 32
    Options
    The amp. I replaced and they blew again.. all correct amps/volts. I was only testing the driver in the jig. Was fine no wires moving nothing...poof...never ends
    · Share on FacebookShare on Twitter
  • crassmage
    crassmage Posts: 32
    Options
    Also 7-11 hz range it was silent. If it stays in place what is good to use to "seal" the magnets? Power grab stuff?
    · Share on FacebookShare on Twitter
  • crassmage
    crassmage Posts: 32
    Options
    Well something gave overnight. Stuck again. I was able to move it back in the job but that pretty much told me my adhesive didn't hold. Sure enough was the case. Try again today.
    · Share on FacebookShare on Twitter
  • pitdogg2
    pitdogg2 Posts: 24,574
    Options
    crassmage wrote: »
    Well something gave overnight. Stuck again. I was able to move it back in the job but that pretty much told me my adhesive didn't hold. Sure enough was the case. Try again today.

    what kind of adhesive are you using?
    · Share on FacebookShare on Twitter
  • crassmage
    crassmage Posts: 32
    edited September 2019
    Options
    I had the loctite red. Also power grab around the bottom. Of magnet with pole plate. Sat for 24 hrs. Took apart very gently.. stuck.. was able to pull it apart easily ...suggestions?
    · Share on FacebookShare on Twitter
  • FestYboy
    FestYboy Posts: 3,861
    Options
    Cleanliness is next to godliness... And the loctite should not push out the seam (one light head in the middle of the radius).
    · Share on FacebookShare on Twitter
  • lawdogg
    lawdogg Posts: 450
    Options
    I use 2-part epoxy and it's never failed me.
    <3 my 3.1TLs

    I will fix your shifted magnets for free. :)
    · Share on FacebookShare on Twitter
  • crassmage
    crassmage Posts: 32
    Options
    I did use minimal amount. I will get some epoxy and give it another whirl
    · Share on FacebookShare on Twitter
  • crassmage
    crassmage Posts: 32
    Options
    fdslh8ktpy9c.jpg
    · Share on FacebookShare on Twitter