How to ruin your day.

[Robh3606]

And I did it all by myself :(

I got my 2435's today from an Ebay auction. Unpacked them, ran them to see if they worked and then dropped one on the floor:banghead: It was one of those slow motion drops when you just know you really did it this time!! It's the first time I have ever dropped a driver. Well needless to say I broke the glue bond between the Neo magnet and the top plate. I called JBL and told them I shifted the top plate on a 2435 and to my surprise I was told it was not repairable!!!!!! Just order a new driver we can't fix them:blink:

Oh hell!!! At this point I figured I had nothing to loose so I got the top cover off and then after some gentle coaxing and taps with a small plastic hammer I was able to get the diaphram out of the gap which promptly slammed shut with nothing to hold the top plate. I tried shimming and as soon as you pulled the last shim it slammed up against the pole piece. I figured I need to get the top plate off the driver so I used the 4 cover screws to slowly jack-up the top plate and I was able to get it free. So now I have the driver in pieces and need to get it back together again. I measured the Top plate and the Pole and it looks like I have an 040 gap. I can't find any info on a gap tool. Does anyone know if there is one for this driver and what the gap should be set at?? I am also trying to figure out what adhessive to use. There is a very narrow glue line on the back of the top plate. What I plan on trying is to reposition the top plate and shim it the best I can and as evenly as possible then add the adhessive and then use screws to lower it back in place. I am hoping once the glue dries I will be able to get the shims out and the top plate will be glued in place like it was originally. Any thoughts and comments are welcome.


Thanks Rob:)

[Zilch]

:(

I'm trying to think of something solvent soluble to use as shims, or softenable, at least.

If brass, predrill a couple of holes so that you can grab them with with, like, a bearing puller to get them out.

May we see pics of the "disassembled" driver, please?

[mbask]

Can you demagnetize all the parts including the neo magnet, then reassemble it? I've done this before with speakers. I was not able to take out all the magnetization , but enough to work with to re center the slug without the agonizing fight with the magnet. when remagnetizing I had to match the magnetic value to the other in the pair
so that the resistance would be the same, I could only get it close but the resistance meassured the same from the lead wires when the v-coil was in the gap. I don't know where you could get that done in NY but i did it at my job as we have a huge re/demagnetizer and measuring insruments. I' am fairly new at this game and it might be a big NONO to do that to JBLs, but hey....ya gadda do wachu gadda do..
good luck .. and thanks for the story I know I have a few OOPS!....DOE!!:banghead: storys i could tell.
mbask:)

[moldyoldy]

Hi, Rob,
I did a live magnet reassembly of some Altec 411s once. I'm not familiar with your 2435s, but assume the task would be similar if the proper shims/bushings can be had/fabbed. As you say, at this point you've nothing to lose. Using full-diameter shims that are long enough to let you start the parts on them before the mag effect begins will help a lot. I first used a Loctite epoxy that was listed for the purpose (400-something), which didn't hold. Finally was successful using tried-and-true JB Weld, (the newer quick-set variety). Maybe something here will help, good luck;

http://audioheritage.org/vbulletin/showthread.php?t=10168&highlight=411+magnet

[Robh3606]

Thanks for the replys. I will get some photo's tonight. I have some .035 soft aluminum that has been rolled into a round shim about 1 1/2 inches high so it goes above where you have no control over the magnets grab power. The 005 sounds like a lot of play but I don't know what the concentricity is for the pole and the top plate. I want to dry fit it all and see if it looks like it will work or not. I took the pole diameter added 1/2 the gap and made the shim diameter centered at that dimension. I think I should be able to get top plate centered before the screws hit the magnet. I going to make damn sure my fingers don't get between the top plate and the magnet on the way down.

Thanks on the glue. I was wondering about that. I had to use a machinists vice to slide the top plate across the magnet to seperate the top plate and pole piece to get the original shims I tried in. The amount of force there is really amazing and I can see how you could get hurt if your not careful. There was no way I could have pulled them apart by hand. What ever glue you use has to be really strong.

Rob:)

[edgewound]

Hey Rob,

Sorry to read about your mis-hap....buuuuummmer.

The gap spec on the 2435HPL is .038"

Good measuring;)
From what I understand, de-mag and re-mag of neo's is a different ballgame than alnico or ceramic. Wish I knew more for you...

[GordonW]

We generally use 30-minute epoxy (can't remember the brand... NOT Locktite... whatever the brand is, from the local Ace Hardware) when re-glueing magnets. Stronger than 5-minute, but not as brittle as JB Weld or the like. Never had one come back apart... and we're talking HUGE magnets like Gauss 15" drivers and such...

The nice thing about 30-minute epoxy is, that you have time to "error-correct" if you have a shim or alignment problem. It's not going to set up before you can get it aligned properly...

Regards,
Gordon.

[Robh3606]

Thanks!!

Hello Edgewound

That gap spec is great to know. I am not sure how this will pan out exactly I may be under a mil or so on one side the way we figured it but I don't think I can get it better than that. I was guessing around .037 and when we did the shim that's what we were aiming for that number.

Hello Gordon

30 Minutes, thats good to know we use it at work as well. That's something I can get easilly and if it works for those it should work for this as well.

Hello moldyoldy

Your thread gave me a bit of confidence and some great ideas.

Hello mbask

When I called JBL and they said they could not demag a 2435 that shot that out the window. I would even try if the factory can't.

Hello Zilch

Pictures as promised. I was thinking a soft material until I saw how much force there was. It will crush plastic.

I got it together as a dry fit and it looks good. With any luck this might work!! Anyone know where to get Ferro Fluid packets to recharge the gap???

Thanks for your help

Rob:)

[edgewound]

Robb,

Make sure you lubricate the gap...topplate and phase plug walls...use silicone grease or DuPont Krytox grease to aid in shim removal....then clean the gap real good with acetone.

[Ken Pachkowsky]

Sorry to hear about your fumble...

I will follow the outcome.

Ken

[Titanium Dome]

...this happened, but your attitude couldn't be better. I like guys who try to fix things and are willing to take a chance to problem solve rather than whine and moan about their bad luck. If you pull this off, you'll be on top of the world.

I'm betting you find a way to get it done, and you'll have had the benefit of a lot of great guys helping you along the way:

Edgewound
Gordon
moldyoldy
mbask
Zilch

Well done! :thmbsup: This is the forum at its best.

[JBLnsince1959]

Sorry to hear about your fumble...

I will follow the outcome.

Ken

me too..what a bummer...we feel for you...

[norealtalent]

...and if you are not happy with the results, you can purchase one of the ebay 2431's for under $100 and swap out your backcap and dia into the 2431 motor. Not as much fun as fixing your own but certainly worth salvaging your driver....

[frank23]

hi rob,

I also bought two 2435's of ebay some months ago and the seller contacted me offering two more for the same price. He might be a good source for another 2435? PM if you want his email.

Frank

[Zilch]

I have never yet gotten a reasonable explanation from any of several vendors of these 243x drivers as to what they are or where they're coming from.

Often claimed to be "new" on eBay, they are obviously not, but they do have the correct diaphragms and work, albeit not to any uniform spec. Best I can figure is they are coming out of tour systems?

[Robh3606]

Hello Zilch

Your right about that. Same for the 2431's. The 2 I just got were in good shape overall however the one I dropped had the diaphram in backwards and I didn't see this until after I got the cover off. It also has a small crease in the diaphram that I certainly didn't put there but I couldn't very well go back to the seller and complain after I dropped it. Point is it was not "New" as advertised but for these prices how can you complain for what you are getting???

On another note EUREKA!!!! It worked:D :D :D I know have a working pair again. I would like to thank you all for your encouragement and ideas all around we should pat our collective selves on the back because we now have a viable repair if anyone else has a whoops with one of these. I tried an epoxy, got the shim out and just watched the top plate creep over to the pole in slow motion. I took a chance and used medium viscosity super glue. It worked like a charm. One thing however, I should have done a better job shimming. I depended on the material thickness and diameter of the shim to help hold the top plate. It didn't work it somehow found the thinnest part to creep towards. I am off -.005 on one side so I am under spec on the gap size over a small portion of the gap. The coil still is free and there actually is quite a bit of room in that gap otherwise I would be toast with that much offset. Really won't know if this worked until I measure the driver. But it sure looks OK for now. The glue is holding.

Hello norealtalent

That is a great idea to use a 2431 core and I had to laugh when I read it cause I didn't even think of it. I was hell bent on getting it fixed and thanks to you guys we did.

I found Ferro Fluid on E-Bay to recharge the driver.

Rob:)

[edgewound]

Congrats Rob....hope it works well.

Zilch...

The source I got my (4) 2435's and (2)2407's from said they came from new Vertec systems that were part of a big nightclub or sound company operation liquidation. Seller was very accomodating to me and offered me more drivers too through e-mail but lacked the funds for more at the time.
He even delivered to my shop:applaud: ...nice hispanic guy...had wife and young kids with him in a nice new SUV.

[grumpy]

Glad to hear this story had a happy ending. :banana:

Prompted me to check mine over and have a listen.
Ferro-fluid present, no creases. I don't have any horns
designed for these (yet), but they should make for some
interesting experimenting :)

:cheers:

-grumpy

[toddalin]

As an alternative to the shims, it would seem that one could wrap the piece with Teflon tape to fill the gap. When the glue dries, the tape could simply be unwound. And the glue won't stick to it.

[Robh3606]

As an alternative to the shims, it would seem that one could wrap the piece with Teflon tape to fill the gap. When the glue dries, the tape could simply be unwound. And the glue won't stick to it.

Hello toddalin

I not to sure that would work. We use teflon at work and one issue it has is cold flow. If you compress it it won't hold it's shape. It's simply too soft. You can only lower the top plate back down in a controlled manner with the screws. The closer you get to the the magnet the more the sideways force towards the pole piece increases. You need a shim that can hold up against this sideways force until you get it all the way down and the glue sets. Those magnets are really powerful. I had a razorblade get grabbed from 6 inches away from under a piece of paper as I put it down on my desk. That scarred me!! I was very lucky I wasn't in the path. It could have done some serious damage to my fingers. If they can't demag them to work on them I can understand why JBL won't fix them. They are an accident waiting to happen when the magnets are fully charged.

Rob:)

[edgewound]

As an alternative to the shims, it would seem that one could wrap the piece with Teflon tape to fill the gap. When the glue dries, the tape could simply be unwound. And the glue won't stick to it.

Teflon tape would most likely be way too soft...and how are you going to measure how many layers to build up to make the right gap shim thickness?

The shim stock needs to be strong enough to not crush under the force of the pole piece attracting the top plate to it.

You're welcome to experiment and show us your results though....maybe I'll learn a new process.

You CANNOT under estimate the pull force going on here....it's extreme!!!

You can hurt your self BIG TIME if you're careless and think this is no big deal.

[moldyoldy]

You can hurt your self BIG TIME if you're careless and think this is no big deal.

And that'll really "Ruin your Day"!

Congrats Rob!

[joe]

suppliers such as enco and msc sell shim stock in all manner of sizes ,materials ,and thicknesses.

[Earl K]

Hi

What a great thread ! :)

Rob, I'm glad you fixed your broken 2435 .
I'm sure the support from the others who weighed in with their thoughts and advice, helped you find a workable solution .

Re; Ferrofluid .

- What did you find ? The stuff comes in many weights / which effects the HF response through coil dampening .
- I'd CLIO the driver before adding anything into the gap. That way you can document the results.
- FWIW ; the last time I checked , Meyers Sound Labs ran ferrofluid in the gap of the compression drivers for their SR products. They ran a dry gap in the same drivers when used in their large studio monitor .

:D