Frozen Monitor 7B woofer (MW6500) repair
LordAragorn
Posts: 36
I have searched this forum for frozen woofer repair and found several threads on how to repair the Polk woofers that have a magnet shift problem.
However I did not find any instructions/ pictures on how to open the woofer magnet before being able to fix the pole magnet in the correct position.
Attached are pictures of my woofer from the Monitor 7B. On the rear of the magnet, I believe, is the back end of the pole. How do I remove this? Searched YouTube too but did not find any videos on how to open this woofer.
1. Can someone please add links to the instructions to open up this MW6500 woofer?
2. Has anyone used the copy MW6500 from Midwest speakers? Do they look the same as the originals and sonically are they close? That would be my last resort.
Appreciate the help!
Thank you
However I did not find any instructions/ pictures on how to open the woofer magnet before being able to fix the pole magnet in the correct position.
Attached are pictures of my woofer from the Monitor 7B. On the rear of the magnet, I believe, is the back end of the pole. How do I remove this? Searched YouTube too but did not find any videos on how to open this woofer.
1. Can someone please add links to the instructions to open up this MW6500 woofer?
2. Has anyone used the copy MW6500 from Midwest speakers? Do they look the same as the originals and sonically are they close? That would be my last resort.
Appreciate the help!
Thank you
Comments
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I forgot how I took mine apart but now that I think about it, I used the device that our member made to push the shifted magnet back into position.
Using that tool, no damage was done to the voice coils by pulling and scraping the coils with the pole pieces. The tool was a design masterpiece!
There's a thread that shows a PVC pipe coupling that has a flared end and that worked similarly to the awesome tool that our esteemed member let each of us use in a chain mailing gifting act. The PVC used screws or threaded bolts to push the loose portion back into position. Then the gluing was performed while the cone was free-floating again.
I wish I had bought the tool he put up for sale! I haven't needed to fix another woofer yet but one never knows.Most people just listen to music and watch movies. I EXPERIENCE them. -
Removed the dust cap and then smashed my T-yoke/pole piece out quickly with a 3/4" oak dowel and a properly sized PVC receptacle held in place by @xschop massive billet aluminum jig. You could use whatever is the right size to clear the T-yoke that has good bearing surface on the magnet and is tall enough to allow the T-yoke to clear the magnet and not be drawn back by its attraction to it. Maybe these photos help:
George / NJ
Polk 7B main speakers, std. mods+ (1979, orig owner)
Martin Logan Dynamo sub w/6ft 14awg Power Cord
Onkyo A-8017 integrated
Logitech Squeezebox Touch Streamer w/EDO applet
iFi nano iDSD DAC
iPurifier3
iDefender w/ iPower PS
Custom Steve Wilson 1m UPOCC Interconnect
iFi Mercury 0.5m OFHC continuous cast copper USB cable
Custom Ribbon Speaker Cables, 5ft long, 4N Copper, 14awg, ultra low inductance
Custom Vibration Isolation Speaker Stands and Sub Platform -
I forgot how I took mine apart but now that I think about it, I used the device that our member made to push the shifted magnet back into position.
Using that tool, no damage was done to the voice coils by pulling and scraping the coils with the pole pieces. The tool was a design masterpiece!
There's a thread that shows a PVC pipe coupling that has a flared end and that worked similarly to the awesome tool that our esteemed member let each of us use in a chain mailing gifting act. The PVC used screws or threaded bolts to push the loose portion back into position. Then the gluing was performed while the cone was free-floating again.
I wish I had bought the tool he put up for sale! I haven't needed to fix another woofer yet but one never knows.
Thank you;
In reference to the second paragraph, I did read one thread where the member used a PVC pipe with two different internal diameters and screws to align the pole piece correctly. Is that the one your are referring to.
As for the first paragraph, I’m trying to visualize but I can’t. Do you have pictures of the tool or a thread on the same? Thank you
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Gardenstater wrote: »Removed the dust cap and then smashed my T-yoke/pole piece out quickly with a 3/4" oak dowel and a properly sized PVC receptacle held in place by @xschop massive billet aluminum jig. You could use whatever is the right size to clear the T-yoke that has good bearing surface on the magnet and is tall enough to allow the T-yoke to clear the magnet and not be drawn back by its attraction to it.
Thank you; I think I’m getting the idea. So basically what needs to be done is that the piece marked A (see the picture below) needs be secured on say a PVC pipe that will hold it in place while allowing the piece marked B (the T-yoke you are referring to?) fall down inside the PVC pipe when you hammer it from the top after removing the dust cover?
If that T-yoke is what needs to be removed, won’t inserting shims between piece A and piece B and then opening with two identical flat screwdrivers inserted from opposite side help (of course ensuring that the pole piece comes out straight so as to not damage the voice coil)?
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Ferrite is a very brittle material so any sort of pry bar activity in trying to separate the two is out in my opinion.
You are correct to be concerned with pulling the T-yoke out in any sort of crooked manner because there is only about 0.007" radial clearance even in a perfectly centered one, to the voice coil.
It is a good idea to try to disengage the voice coil from the gap by pulling the cone up evenly and having it held that way, before trying to remove the T-yoke. Next time I do this I will do something like that. Something like a couple of wood dowels wrapped in foam and fed through the windows so that the cone is held upwards. Rubber bands around them and the frame may help too.George / NJ
Polk 7B main speakers, std. mods+ (1979, orig owner)
Martin Logan Dynamo sub w/6ft 14awg Power Cord
Onkyo A-8017 integrated
Logitech Squeezebox Touch Streamer w/EDO applet
iFi nano iDSD DAC
iPurifier3
iDefender w/ iPower PS
Custom Steve Wilson 1m UPOCC Interconnect
iFi Mercury 0.5m OFHC continuous cast copper USB cable
Custom Ribbon Speaker Cables, 5ft long, 4N Copper, 14awg, ultra low inductance
Custom Vibration Isolation Speaker Stands and Sub Platform -
The magnificent tool screwed to the silver plate attached to the frame. That does not move.
Then the magnet-aligned screws ( there's 4 quarters to work on. Some are loosened out of the way. ) are tightened to push the magnet back to where it was. 4 screws, 4 options. Tighten or loosen.
It's obvious in the beginning which way the magnet shifted. I remember using 2 screws to push worked best.
My PC crashed and I had my photos put on a thumb drive at Best Buy. I'm 99% sure I took photos of some of the 6 or so woofers I fixed using that tool.
I haven't put the thumb drive back in to look at the photos yet. Maybe today in a minute when I find the packet with the thumb drive in it.Most people just listen to music and watch movies. I EXPERIENCE them. -
I hate computer steps to get stuff done!
Any way...I got pictures from the thumb drive to appear. I tried to copy them to a folder under "Pictures" but something went wrong... Oh well.
Most people just listen to music and watch movies. I EXPERIENCE them. -
The magnificent tool screwed to the silver plate attached to the frame. That does not move.
Then the magnet-aligned screws ( there's 4 quarters to work on. Some are loosened out of the way. ) are tightened to push the magnet back to where it was. 4 screws, 4 options. Tighten or loosen.
It's obvious in the beginning which way the magnet shifted. I remember using 2 screws to push worked best.
My PC crashed and I had my photos put on a thumb drive at Best Buy. I'm 99% sure I took photos of some of the 6 or so woofers I fixed using that tool.
I haven't put the thumb drive back in to look at the photos yet. Maybe today in a minute when I find the packet with the thumb drive in it.
Thank you!
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I hate computer steps to get stuff done!
Any way...I got pictures from the thumb drive to appear. I tried to copy them to a folder under "Pictures" but something went wrong... Oh well.
Wonderful! Thank you so much Tony M!
I think the key is to make a tool like you did & align the pole piece and the magnet so the coil moves up & down freely; correct?
Did you custom make the tool on lathe? I can make it but need a lathe LOL. Or did you use some part or something that is available in a store? I’m looking into options myself. I’m thinking PVC pipe with nuts glued inside a hole and put bolts on 4 sides to hold the pole piece and magnet - similar to your tool but made of PVC. Thoughts? -
This thread has some really good info...https://forum.polkaudio.com/discussion/197152/diagnosing-fixing-shifted-polk-mw-drivers/p1
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This thread has some really good info...https://forum.polkaudio.com/discussion/197152/diagnosing-fixing-shifted-polk-mw-drivers/p1
Perfect; exactly what I was looking for! Thank you, joebass3!!🙏
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OH NO...I didn't make it.
That requires some special kind of skills I've never possessed.
Most people just listen to music and watch movies. I EXPERIENCE them. -
Update: I was able to pull apart the pole piece, magnet & the basket with the top plate on it. One thing I totally missed is to check orientation of the magnet but while trying to separate it from the pole piece, it was chipped. I then removed the pole piece + the magnet from the top plate first and then the pole piece from the magnet.
Removed the glue from everything; feels clean to the touch the voice coil looks un damaged and the coil with the cone moves in and out freely. Spider looks good. Will clean everything with alcohol, let it dry and then start with the surgery LOL.
Attached are pictures of everything taken apart. Thank you @joebass3 for sharing @lawdogg’s original thread. I was totally lost without the thread about how to disassemble everything.
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Dust cap removed, cleaned everything. Pole piece attached and aligned with the magnet.
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For the record, drivers are not magnetized until after they are glued up and dry when being built originally. It is just a non magnetic ferrite ring in the beginning.
