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 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

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!! 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/s...ght=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! 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?