Model 10 with Stiff MW6500s/ and crack in back

khoregon

Hello,
I'm brand new to the forum, so please gently correct my misuse of terms/names/descriptions.

I have a model/monitor 10 speaker from 1980 (recently from a Goodwill store). Both mid drivers/cones stiff, locked up on one speaker, no audio. These, I believe are the MW 6500's.

Also no audio through bottom woofer. Wires appear fine.
The speaker also has a crack in the plastic in the back and the fuse setting has a small wobble. When I push on the bottom woofer center (gently of course) air comes out that back plastic crack.

What do you suggest? Should I replace the MW6500's and the back unit--what is it called?--- too? and... new if available vs used?

Thank you for your time and consideration.
-Keith

PS: I'm a new Club Polk member and like others--I sure enjoy seeing photos--so I'll try to post several.

phocion

Welcome to Club Polk!

The bottom "woofer" is actually a passive radiator, so it will not move unless the mids are working. I would clean off the fuse holder and replace the fuse right off the bat, corrosion can lead to odd audio problems. You should also be able to tighten it, and fill the crack on the x-over if you so desire (super glue would work, looks like someone already tried though).

Once you get the fuse situation worked out, we can go over the mids and magnet slippage If you want to read ahead, look at this post: http://www.polkaudio.com/forums/showthread.php?t=102923&highlight=magnet+jig

Rev. Hayes

Welcome!

Nice speakers (you do have 2 of them right?) and well worth fixing in my mind.

I literally just finished replacing a MW 6500 in my Monitor 10's five minutes ago and they look just like yours. I got the driver through the club polk for sale section. you can often find drivers to match yours from other members.

As for the woofer; it's doing just what it should since it is in fact not a woofer. It is actually a passive radiator that acts like a tuned port would in a ported speaker. It wont move at all unless the two MW drivers are working.

As for the cracked terminal cup you should definitely replace it as the escaping air will cause your bass to suffer a great deal. I have one from the same version Monitor ten that I have just been using for parts. Let me know if you might like it.

halo71

khoregon, welcome to the forum! Those are really worth your time to fix I can promise that. I am guessing you got them/it pretty cheap right? With that terminal cup being broken I would take it out, replace it as said. And look closely at the XO for any damage on it.

And peerless tweeter(s) to boot!

HB27

Welcome to the Forum.
Nice speakers and worth re-doing.
Replace the terminal cup or repair. I've used "J-B Kwik" with good results on the plastics and to secure the midwoofer magnet structures so they won't slip and lock up.
Remember the cabinets must be airtight so the passive woofer will work properly.
I've got a Midwoofer with the gasket on it IF you need one.

khoregon

Thanks so much for your kind welcome and replies. I'll reply with more soon as I consider the choices. Glad to hear from you.
And yes I got the pair of these Polk 10's for $19.95 at a Goodwill in Southern Oregon. (I'm just getting into some vintage stuff: also got a pair of refoamed Epicure 5's recently and a cheap old Rotel receiver (both on Craigslist) and I'm very pleased).

Toolfan66

Congrats!! And good luck!!!

khoregon

With the crack in back--there seems to be some consensus to replace the "terminal cup". So, yes Rev. Hayes, I'd be interested in your offer. How do we reply offline privately?

Another question for a Polk 10 rehabilitation: if the MW 6500's are stiff--that means the magnets slipped or what? If so, what's the usual course of action? (non engineer type here). and..Is it ok to ask the members if they have these for sale? Thanks.

phocion

Sometimes the glue that holds the magnets in place gives way due to shock, such as dropping the speaker. It creeps out of alignment, pinching the wire coil against the magnet, and causes friction or even a complete freeze. You can try to fix it yourself, before seeking replacements, by looking at the thread I mentioned earlier and trying to re-center the magnet. Once you get it set, JB-weld that sucker down and enjoy

If that does not work, there is a For Sale area on the forums, they show up on sites like Ebay, and you can even call Polk customer service for a replacement.

I wouldn't worry about the crack too much if you can close it with glue, but karma parts are always nice. You might have to have 20 posts before you can PM in the forums, I forget the number...

khoregon

Thanks Phocion,
I appreciate your thoughtfulness and explanation. I did look at that thread to re-center the magnets, but it looks like a project beyond my scope at present. I'll try glueing the crack and consider replacing the 6500's. I'd love to hear these 10s in my small living room.
I worked at a radio station in Chas. SC in the 80's and we had a saying: "kneel and remain silent, an engineer is passing".

phocion

Well, I am not an engineer, but I did sleep at a holiday inn express last night...

Worst case scenario is that you destroy a broken speaker and learn something. Best case is that you fix it While the jig looks complicated, it is really about very slight movements to the magnet to allow the wire coil to travel freely. This is something you could do by hand and eyeball if you wanted to. Basically, take a look at the magnet, if it seems a little off center, try to gently slide it to center, and if you encounter resistance, stop, and back off a bit. Then, try to move the cone. Keep making small adjustments until it travels freely with no scraping sounds. Plug it in and see if you got lucky If you did, wunderbar + JB-weld to keep it in place!

kefranklin

Congrats on the monitor 10s and welcome to CP. Whether repair or replacement, the people on this forum are willing to help with anything. Hopefully you will be able to have a listen before long. Also, greetings from sunny South Carolina. I see you have traveled far, far away from this place. Good choice, since we have no quality gear in our Goodwill.

khoregon

No matter how far away--there's still a bit of Carolina on my mind.

and Phocion--thanks, I'll follow your instructions. (and get some JB-weld!).

geppy1

I may have two of the exact ones you need mid week. let me know Keiht

tincandriver

Likely the voice coils are fried to the magnets in the drivers. I've heard that this is repairable, not sure. Usually when I see a speaker in this condition, it's because of abuse. So you might consider replacing them with the same model of speaker used. Also, your crossovers might be fried too, I't not the end of the world. You can locate whole used crossovers or just spec the parts and replace. The caps, coils, and resistors are marked to value. Also if it is a 10A monitor, check the fuse in the back. It could be blown and the rest of the electronics OK. Hope this helps.

mmadden28

phocion wrote: »

...While the jig looks complicated, it is really about very slight movements to the magnet to allow the wire coil to travel freely. This is something you could do by hand and eyeball if you wanted to. Basically, take a look at the magnet, if it seems a little off center, try to gently slide it to center, and if you encounter resistance, stop, and back off a bit. Then, try to move the cone. Keep making small adjustments until it travels freely with no scraping sounds. Plug it in and see if you got lucky If you did, wunderbar + JB-weld to keep it in place!

Not sure if you ever tried that 'by hand', but I don't see how that can work (well at least I tried many many times). I think the only way to fix it is with a jig of some sort. When the glue fails the pole slips out of alignment because of the magnetism and so the pole piece is magnetically attracted to the other half of the assembly, thus pinning the Voice Coil (VC) to the side wall, and this is a seriously strong attraction. If you tried to move the pole piece manually it is extremely difficult by hand and because of the continually present magnetism it's just going to re'stick' to another spot. Of course each time you do this you risk damaging the voice coil.

khoregon wrote: »

Thanks Phocion,
I appreciate your thoughtfulness and explanation. I did look at that thread to re-center the magnets, but it looks like a project beyond my scope at present.....

I expect to be posting detailed step by step instructions for making that jig and how to repair the driver in the next couple weeks while I'm home from work. If you have a slipped magnet on your driver, it's worth a shot. As Phocion mentioned, the jig does its job by allowing you to make small adjustments to center the alignment of the pole piece, thus freeing up the VC. Then its just glue, cure and play.

phocion

mmadden28 wrote: »

Not sure if you ever tried that 'by hand', but I don't see how that can work (well at least I tried many many times).

I might have been lucky. I had one MW that was scratchy, so I made it worse by moving it around (frozen), then got the alignment right. My tactic was to gently rock it back and forth to nudge it toward true.

mmadden28

Hmm I thought I replied already-well here we go again...

If I had to guess, you probably had a partial glue failure--I didn't think that was possible as I thought the glue became brittle, but I guess it can partially fail and still hold on somewhat as it apparently did in your case. Cool for you. :cool: I guess that's what happens when some driver get scratchy--perhaps they are in the process of failing.

khoregon

Ok, continuing my naive home investigation and potentially entertaining and ignorant effort to repair Goodwill-bought Polk 10's.

Thanks for all this input. I don't yet qualify for private email miles yet...as I haven't hit 10 postings here--but will get there soon.

I tried, by hand, to recenter the magnet on both my mid MW6500s. The magnets can turn slightly and I experimented a bit, but the cones are still stiff. I even said several magic words.
I think they are scrogged. So, this puts me in the position of finding 2 MW6500's or the compatible 6503's, yes?

And in looking closely at the top of one of the magnets--those look like heat marks? Normal? It is from 1980 after all, so perhaps it has been hit by lightning in the last 30 years.

My other issue is that back terminal cup (is this also called the "cross over input panel"?). It has one big crack and is broken on the top left of the fuse holder. The bare screw/bolt underneath is exposed. Glad to get your response.

Thanks,
-KH

Outfitter03

Replacement Crossover.

http://cgi.ebay.com/Polk-Audio-Monitor-10-Crossovers-Pair-Vintage-/290499245768?pt=LH_DefaultDomain_0&hash=item43a31ab6c8#ht_1022wt_905

mmadden28

khoregon wrote: »

Ok, continuing my naive home investigation and potentially entertaining and ignorant effort to repair Goodwill-bought Polk 10's.

...

And in looking closely at the top of one of the magnets--those look like heat marks? Normal? It is from 1980 after all, so perhaps it has been hit by lightning in the last 30 years.
...

Any effort is a good effort-nothing ignorant about it. :cool:

I don't think that is a burn mark--I think its just the way the magnets look when certain glues are applied--I'm pretty sure the same or similar rainbow effect is present in the area where glue was on my old magnets.

Once its determined that the XO itself is not damaged--you could just get a binding post plate/terminal cup from somebody that is parting out their old speakers, or just patch the plastic on the one you have with a glue or epoxy. I'm not sure if Polk still has the terminal cup available for purchase or not.

If you get new/replacement drivers, hang on the the failed ones to attempt a repair on them-Don't just throw them out.

halo71

khoregon, see this link that is about fixing your problem with those drivers.

http://www.polkaudio.com/forums/showthread.php?t=102923

mmadden28

halo71 wrote: »

khoregon, see this link that is about fixing your problem with those drivers.

http://www.polkaudio.com/forums/showthread.php?t=102923

That's my incomplete thread--I should have it done hopefully this week, if not next week.

halo71

Sorry, I posted with that link about the same time you were posting above.

dorokusai

halo71 wrote: »

khoregon, see this link that is about fixing your problem with those drivers.

http://www.polkaudio.com/forums/showthread.php?t=102923

I like Mike but his success with a couple doesn't translate into spending money to ship drivers to him. Unless he's into that...which by all means send ALL drivers to mmadden, he can always fix them. What if the fix turns the driver into a 6503? or 6511? Until we wiggle some parameters from Polk, fixing a driver doesnt really mean anything except it works.

I commend Mike on his efforts and it may pan out to be very cool. Right now, there's just too many variables that no one knows about to say the word "fixed". Sorry to be a downer but it's reality. Mike means the best and personally is someone who cares everything about our forum.

halo71

Well I was kinda thinking khoregon might have a go at building his own jig.


This link is in that thread as well.

http://www.audiokarma.org/forums/showthread.php?t=130808

Rev. Hayes

This terminal cup/x-over is yours for the cost of shipping if you want it.

Don't give up yet. Those can still be some amazing speakers!

khoregon

Yes, Rev. Hayes, for the terminal cup...
How do we reply off-line?
Thanks,
-kh

phocion

khoregon wrote: »

I tried, by hand, to recenter the magnet on both my mid MW6500s. The magnets can turn slightly and I experimented a bit, but the cones are still stiff. I even said several magic words.
I think they are scrogged. So, this puts me in the position of finding 2 MW6500's or the compatible 6503's, yes?

Well, it was worth a shot. The 6503 is the replacement for the 6500, and you can find them on ebay pretty regularly, 6500 less so.

http://cgi.ebay.com/Polk-Audio-MW-6503-Mid-Woofers-SDA-CRS-Monitor-Pair-/180587796494?pt=LH_DefaultDomain_0&hash=item2a0bdf180e

Seller actually has 2 pairs from a set of monitor 10's

ncbuckeye3

halo71 wrote: »

Well I was kinda thinking khoregon might have a go at building his own jig.


This link is in that thread as well.

http://www.audiokarma.org/forums/showthread.php?t=130808

I think this is a better link:

http://www.audiokarma.org/forums/showthread.php?t=202963

Rev. Hayes

I think I just sent you an email through the CP "send and email" system....

If you reply then I will assume you got it.
Post here if I did it wrong and you did not receive an email.