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Multi-Way Conventional loudspeakers with crossovers

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Old 17th January 2013, 08:01 PM   #11
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Quote:
Originally Posted by Jennerz View Post
I need to remove the woofer from one of my JBL S36AWII's - so that I can get to and remove a cracked crossover board, deep inside the enclosure - to then be able to try and repair it.

What is the most effective way of breaking that weather-resistant seal - that has the woofer attached to the box - without damaging either the woofer or the enclosure?
Probably just need careful try-it-and-see because many modern products are not built with any consideration of repair, so not intended to be disassembled.
Careful work with paint scraper or similar to mechanically separate the woofer.
There are some products to de-bond sealants. One is in the WEST Marine website, for yacht repairs. Need to be careful not to affect any other plastic parts. Difficult to predict unless you know exact composition of sealant etc. Box is made of ?
At least the board repair is obvious, just solder wire jumpers across broken traces. Unlikely to be any problems with internal breaks of components.
Tell us how it works out, best of luck.

David

Last edited by Dave Zan; 17th January 2013 at 08:19 PM.
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Old 22nd January 2013, 03:41 AM   #12
Jennerz is offline Jennerz  United States
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Default Cracked Cross-Over Board - Needs Help

Thanks to everyone for their help so far. Great learning experience.

Next request for assistance: How do I approach fixing the cracked board?

I was finally able to get the woofer dislodged from the enclosure. The trick that finally worked was to use a heat gun, which made the seal plyable enough to pry the woofer off the plastic - and with no damage.

Now for the repair.....

I have attached three images of the cracked crossover board:
1. The first highlights two cracks that exist. The red solid arrow is the obvious, major one - I assume that is the only one that will need to be fixed. The yellow with red outlined arrows point to a micro-crack...it doesn't appear to go through the board.
2. A general picture of the PCB.
3. A close-up of the board and the crack(s).

If someone can tell me how to approach fixing this (these) cracks, I would really appreciate it. As I mentioned in a previous post...these are my only speakers - and I really want to get them back and running. THANKS!
Attached Images
File Type: jpg JBL AW36's Board's Crack - edited.JPG (453.2 KB, 49 views)
File Type: jpg JBL AW36's Board's Crack.JPG (494.8 KB, 49 views)
File Type: jpg JBL AW36's Board's Crack Close-up.JPG (509.7 KB, 43 views)
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Old 22nd January 2013, 05:59 AM   #13
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Nice to learn that you were able to remove the woofer.
I would just solder bare copper jumpers across the cracks as drawn below.
After a test that all is fixed you could reinforce the board with a quick-set epoxy and cloth. Glass cloth would be nice if you can obtain the small piece you need as an off-cut, but hardly worth the cost if you have to buy a yard or some similar minimum. Just a few layers of cotton would work fine. Or any simple reinforcement that you can do cheaply, a scrap of plywood and glue would be fine - Be proud to use appropriate tech

Best wishes
David
Attached Images
File Type: jpg JBL AW36's Board's Crack Close-up.JPG (234.1 KB, 42 views)

Last edited by Dave Zan; 22nd January 2013 at 06:05 AM.
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Old 22nd January 2013, 10:49 PM   #14
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Jennerz, Dave's method is simpler than my PM one... just be quick with the solder so the components don't pop out of the hole. If you're not used to soldering, make sure the iron is nice & hot, & use rosin core solder. Tin your wires first - i.e. melt some solder onto the ends before you solder them to the board. Practise on some wire first to get a feel for how it's done. (Having three hands helps...)
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Impedance varies with frequency, use impedance plots of your drivers and make crossover calculations using the actual impedance of the driver at the crossover frequency
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Old 23rd January 2013, 01:33 AM   #15
Jennerz is offline Jennerz  United States
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Would stripped-off thermostat wire be about the right gauge of copper for jumpers?
(I have that or phone wire - but that seems way too thin.)

I am completely confused about the epoxy step....am I basically sealing in the entire board from the bottom? I assume I am trying to keep the board from shifting and separating once I re-assemble it? And when you mention epoxy - is JBWeld the sort of epoxy you are referring to?

Thanks! Jennerz
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Old 23rd January 2013, 04:11 AM   #16
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re:"right gauge of copper" as heavy as you can get, as a min use the wire the same gauge as going to the drivers
re:"am I basically sealing in the entire board from the bottom?' - no just giving it some structural integrity
no idea what your local brands are, I use Araldite here
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Impedance varies with frequency, use impedance plots of your drivers and make crossover calculations using the actual impedance of the driver at the crossover frequency
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Old 23rd January 2013, 08:50 AM   #17
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Quote:
Originally Posted by Jennerz View Post
Would stripped-off thermostat wire be about the right gauge of copper for jumpers?
(I have that or phone wire - but that seems way too thin.)

I am completely confused about the epoxy step....am I basically sealing in the entire board from the bottom? I assume I am trying to keep the board from shifting and separating once I re-assemble it? And when you mention epoxy - is JBWeld the sort of epoxy you are referring to?
I don't know what size your thermostat wire is but around a millimetre or so in diameter of copper would be a reasonable minimum. Just a scrap of stripped speaker wire would be fine or any mains wire, from an old appliance power cord etc. Only upper limit on size is what is practical to solder.

You are correct, the epoxy is just to hold the board so it doesn't break and crack any more. Any method to do that is fine, Pete is correct - it is not essential to seal the board. JBweld or any non-water based adhesive will work, after a bit of consideration I think of plywood and one of the quick-stick adhesives would be even easier than saturation of cloth with epoxy - less drips.

Best of luck
David
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Old 24th January 2013, 08:51 PM   #18
Jennerz is offline Jennerz  United States
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Default We have a Winner!

Thanks to everyone who helped me through this!

I now have TUNES again.......

Was worried that the repair would noticably change the sound quality - but if it did, it's too insignificant to tell.....and after a glass of good Australian Shiraz, they may even sound better than they did before.

Thanks again, so very much. Jennerz
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Old 26th January 2013, 05:26 AM   #19
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Originally Posted by Jennerz View Post
I now have TUNES ...
Excellent What did you eventually do?

Best wishes
David.
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Old 29th January 2013, 08:58 PM   #20
Jennerz is offline Jennerz  United States
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David - I followed your suggestions (as best I could) to the "T". After completing the soldering - using 14 gauge stranded speaker wire as the jumpers - I attached luan (same dimensions as the PCB) as the base to hold it secure. Because the PCB was originally attached to the enclosure using six screws, I did not use much epoxy to lock the PCB to the luan - just enough to snug it, and then I used six longer screws to make it one unit (luan and PCB) as it attached to the enclosure. It was a great learning experience - one that I hope I never have to repeat - but now I know I can do it. Thanks for all your help! Jennerz
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