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View Full Version : Can I dismentle LE85 driver to check its diagram myself?



chen_sp
06-17-2003, 12:39 AM
hi experts,

Recently I found of my le85 driver had a little bit problem.

One problem is its impendance curve is quite different with another one.

And it sounds a little bit lower than the good one and sometimes it sounds a little bit noise, e.g. 'ka ka'. I guess maybe its diagram has some problem. Am I right? Do you think it's safe for me to dismentle its cover to have a look its diagram? How to dismentle le85driver(Do I just un-screw the four screws on rear?)? Thanks in advance.

Mr. Widget
06-17-2003, 01:01 AM
Sure, four screws and you are in.

Sounds like a burnt coil to me though, not much to see. When you remove the cover you will see the diaphragm. There are two leads from the rear cover to the screw terminals on the diaphragm, disconnect these from the edge of the diaphragm and then you can loosen and remove the diaphragm. Be very careful of the magnetic force, if you slip your screw driver will be pulled into the diaphragm. I doubt there will be much to see though.

Good luck!

chen_sp
06-17-2003, 01:15 AM
Thank you for help.

Do you mean if I'm not careful, the diagram will be damaged because of the magnetic force? How about I use a plastic screw driver?

Mr. Widget
06-17-2003, 01:37 AM
A plastic screw driver would be ok... still be careful about slipping, I've never done it, but it would be easy to do.

"the diagram will be damaged because of the magnetic force?"

No, just mechanical damage. The diaphragm is very delicate.

chen_sp
06-17-2003, 02:01 AM
Thank you, I'll try it carefully.

scott fitlin
06-17-2003, 01:41 PM
whenever your working on ANY compression driver you should always use a non magnetic screw driver. Anyway, the Ka-ka your hearing might indicate a cracked diaphragm. If the aluminum surround is cracked it will make a noisy sound. If this turns out to be the case just have the diaphragm replaced. And if this is your problem, it indicates excessive low frequency. Whoever had it didnt have it crossed over correctly!

sa660
06-18-2003, 09:26 AM
Chen_sp,

It is probably the suspension that crack.
If you place a light on the oposite side of the suspension you may see some rays passing through the suspension.
Is the dome is crack you will need to replace the diaphragm? (best replace both)

You will have to be very careful as the gap between the coil diameter and the LE85 face palte is smaller than usual 2420/2470.


You could be lucky and you may clean the gap where the coil is moving and remove some offending dust.

Good luck

chen_sp
06-18-2003, 08:04 PM
Thanks all of you for your help.

I dismantled the rear cover, diagram and re-installed the diagram carefully yesterday. I'm very lucky, I think, the le85 does work perfect without any problem.

Widget, you're right. The screw driver was pulled into the diaphragm while I sliped the screw. But it seems no problem because my screw driver is not sharp. Next time, I'll do it very very carefully.

scott fitlin
06-18-2003, 08:48 PM
I learned to use a non magnetic screwdriver years ago with the same experience! It was my first time changing a diaphragm and the magnetic force pulled my screwdriver right into the aluminum! I had to buy another! After that, I also went out and bought a NON MAGNETIC screwdriver! Simple solution that resolves that little problem forever! :D

Doctor_Electron
06-19-2003, 04:23 AM
"IF WE CAN'T FIX IT...IT AIN'T BROKE!"
Some years ago, I got several 2405's in a trade. They had been in P.A. cabs, having spent many hours soldiering on selflessly in clubs & bars.
During the routine inspection/testing I always perform on used gear, I pulled the drivers apart, finding on each diaphram a nasty hairball coating, cemented together by some sort of fluid (don't ask; don't smell) that had coalesced and dried out. One diaphram additionally had damage in the form of corrosion...discoloration of the aluminum, groady white mush, & some small holes perforating the metal.
Since the voice coil DC resistance was in spec on each unit, I carefully cleaned the mess out of each one, and repaired the holes by applying a coating of clear nail polish to that diaphram (nothing to lose here anyhow). After re-assembly the drivers worked fine.
I used a standard screwdriver to break the screws loose, then unscrewed them the rest of the way with a nylon "tweaker" (radio I.F. transformer adjustment tool).
I worked on those 2405's carefully, the first such components I'd messed with... but I was doing "microsurgury" on aircraft electronics & cockpit instruments in my late teens, after fortunately having received around 300 hours of training in such work in the U.S. Navy.
Anyone handy with tools can work on drivers, assuming the right implements are on hand, and the repair person exercises reasonable care, and is patient while working on them.
BTW, when disassembling & re-assembling drivers such as 2402, 2404, 2405 etc., be absolutely sure that the cone or slot in the center is not allowed to move while you are loosening or tightening the screw that fastens it...if not, the center piece may stick to the diaphram and destroy (and I mean DESTROY) the diaphram when it rotates along with the screw.

zzmagwheels
12-30-2007, 08:31 PM
i have le-85 and dont sound like they used too so im pulling them apart to check for cracks and whatnot. any help. i think they sound a bit scratchy or tinty.

i should mention these are L-200's my favorite loudspeaker of all time

thanks

SMKSoundPro
12-31-2007, 12:21 AM
Dear zzmagwheels,

Welcome to the forum.

Taking apart a le85 compression is no big deal. Take the four phillips screws out of the back cover and examine the diaphram inside.

It is aluminum and thin like a pop can. Sometimes the surround area gets brittle from overuse and age. If its shattered in a milion poeces, clean up the mess and install a new JBL D16R2421 diaphram.

And while you're at it, do the other L200 le85 at the same time. There is nothing in this world like a brand new pair of dias to remind you how great they sound!

Any more questions, just please ask! There are many knowledgeable forumites here that are ALL JBL heads!

Good luck and Keep it simple!
Happy New Year!

Scott.

Harvey Gerst
12-31-2007, 10:18 AM
When I was replacing diaphragms, I used a metal screwdriver, but I would cup my hand slightly around the ring, so that the diaphragm was protected from possible screwdriver slipping. I'm not sure a plastic screwdriver could break loose some of the screws when they're really tight.

I'll try to draw, or take a picture, showing what I mean.

Mr. Widget
12-31-2007, 12:25 PM
When I was replacing diaphragms, I used a metal screwdriver, but I would cup my hand slightly around the ring, so that the diaphragm was protected from possible screwdriver slipping. I'm not sure a plastic screwdriver could break loose some of the screws when they're really tight.I always do that too... if you can find a non magnetic stainless steel screwdriver that would be handy.


Widget

subwoof
12-31-2007, 12:44 PM
I have a screwdriver that is hung from the ceiling on the test bench - even if I let go it couldn't reach the diaphram ( it is adjustable ).

I have dimpled my fair share in the last 30 years...

Remember the one obscure murphy's law:

"A dropped screwdriver will obey the laws of selective gravation and cause the maximum damage". In the consumer world it is referred to as the buttered side of toast anomaly.

sub

edgewound
12-31-2007, 12:50 PM
In the consumer world it is referred to as the buttered side of toast anomaly.

sub

Then...Butter your toast on both sides.;)

Harvey Gerst
12-31-2007, 01:08 PM
We just used plain old screwdrivers at JBL, nothing fancy.

speakerdave
12-31-2007, 01:28 PM
. . . . the buttered side of toast anomaly.

sub

Oh, yeah, the jam-side-down rule.

zzmagwheels
01-01-2008, 06:29 PM
I used a Geber multi tool screwdriver as it is stainless steal which is much less attracted to magnets with no problems.

I have taken one apart and the screws are corroded so there were some particles floating around in there. Also the foam is bad on the back cover it flattens out as I touch it and is falling apart. Is the foam necessary?

I have cleaned up the screws and just need to replace or remove the foam. If the foam is important does it actually touch the diaphragm, or just come close?

The diaphragm looks perfect and no cracks when held up to light.

I cleaned the gap with double sided tape and blew it out with compressed canned air.

Hope I am doing it right.

SMKSoundPro
01-03-2008, 11:34 PM
zzmagwheels,

Sounds like you're doing just great!!! (I never thought to use a Gerber "stainless steel" multi tool! Brilliant!)

Call JBL PRO for new foam, or shout out to EdgeWound. He is recone station and probably has more info than I.

Let us know of your progress. There is no greater way to truly appreciate the JBL world than to climb on in and see how it is made!

Good luck!

Scott.


[Hope I am doing it right.[/quote]