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View Full Version : LE-85 Diaphragm Removal and Replacement



Regis
06-13-2005, 08:37 AM
Before attempting this, you should be mechanically and electrically proficient. If not, then you should have this done by knowledgeable people. You should possess good quality tools as well. I use the micro-tech screwdriver set from Craftsman with hardened tips as well as a Craftsman electronic plier set. An unmolested medium Craftsman phillips for the drivers/transducer is necessary as well. You don't want to strip out screw heads doing this.

First step is to remove the driver from the cabinet. For the L-300, it is highly recommended that two people perform this operation. The driver is heavy and because of the ten pound magnet at one end, it's like handling half of a 20 lb barbell, no easy feat in the confines of a speaker enclosure. For the L-300, you first remove all the OUTER screws on the removable panel in the back of the speaker cabinet. Do not remove the inner screws, these are for the wood bracing for the motor itself. Pull the back panel off, as the midrange unit will now be supported by the front of the enclosure. The back panel is a very tight fit and you may have to reference the next step and loosen the screws around the horn mouth before the panel will come off. The panel is directional to accomodate the upward slant of the motor (there is a small wooden wedge on the bottom brace to take up the difference between the top of the canted motor and the bottom).

Regis
06-13-2005, 08:38 AM
Next. loosen the four screws around the horn mouth, while having person #2 in the back to support the motor. These four large phillip screws are very, very tight, having been torqued down to at least 50-70 lbs of torque. You may even want to have the other person brace the whole cabinet as I did, so you could apply all your weight to the screwdriver while torquing it, so you won't strip the head. The screws actually come loose with a loud crack. Remove the screws while the other guy holds the back of the motor in place and then, back the horn out of the square hole in the back and drop the MF unit down and out through the front of the enclosure.

Remove the three bolts holding the horn to the motor. You may have to tap the front edge of the horn against a thick piece of cardboard or carpet gently to break it free from the motor as ours didn't fall off, but was stuck on there pretty good. Holding the motor with both hands, tap the horn mouth on the carpet and it 'broke' right off.

Regis
06-13-2005, 08:40 AM
Next, remove the four screws on the back of the motor and remove the cap off've the motor. You will find out if your motor has locating pins or not. If your motor has locating pins for the diaphragm as mine did, the following applies. If not, then an alternate set of instructions will follow.

Regis
06-13-2005, 08:41 AM
(motor with horn removed)

Regis
06-13-2005, 08:44 AM
Motor innards (without diaphragm). Note the three diaphragm body screws and the very small dual locating pins. The brass part in the center is the phase plug

Regis
06-13-2005, 08:45 AM
Remove the old diaphragms and put them in a safe place. Unbox the new diaphragm and find the two opposing holes in the black plastic body of the outer diaphragm ring. Handle the diaphragm with great care! With the dome facing up, match the holes to the locating pins and install gently. You will notice immediately that the diaphragm only goes halfway down the pins and doesn't seat. This is normal, as JBL held this to a very tight tolerance and the bottom half of the locating pins is actually a press fit. With your finger or the end of a screwdriver, alternatively tap each side of the black plastic ring gently and you will see the body moving down towards the motor. When the new diaphagm is flush with the motor on all sides, you are ready to install the screws that hold it down. These screws should only be tightened just past being snug. Do not overtighten and warp or crack the body!

Regis
06-13-2005, 08:46 AM
Gently tightening screws...

Regis
06-13-2005, 08:47 AM
Next, take the cap and locate the red or positive terminal and align the cap so that the red terminal is on the same side as the red screw head on the diaphragm. Install the wires underneath the lugs, snugging the screws down, just past being tight, again, do not overtorque or overtighten. It's a diaphragm, not an engine block. Remove any dust or debris (there was a tiny piece of styrofoam from the diaphragm packing) from the area before replacing the cap and install the four screws, securing the cap to the magnet. I tested the first one using vocals and music and it performed perfectly with no distortion from voice coil rub. With the locating pins precisely centering the diaphagm, it's not necessary.

If there aren't any locating pins, then you'll have to use a test tone and from what a more experienced member of this forum has told me: "The centering frequency for the 1" compression drivers is usually 550 Hz and a sweep is performed up to something like 1200 Hz to ensure the diaphragm is indeed centered properly." As I haven't done this, anyone can feel free to add to this thread concerning this. I had freeware for WinSD (?) to install on the PC just in case and I was going to run an integrated amp off've the RCA jacks on the PC, using a very low wattage level to perform this, but since I had locating pins, this wasn't necessary.

Regis
06-13-2005, 08:48 AM
Intall the horns back in the cab and enjoy. Again, two people made the installation of the clumsy horns much easier. I have done this by myself and it is a major wrestling match wrapping your body around an 85 pound cabinet with one arm holding the ten pound motor up on the back side while attempting to put in the horn mouth screws on the front side. Do not attempt this as I actually injured myself, pulling a shoulder blade muscle (and I am very fit). The D16R1421 diaphragm has an extended range over the decades old original diaphragm and are also much fresher (think of a twenty five year old beer can). There was a noticable difference in the sound (not a huge difference), but a difference enough. If I missed something or you'd like to ask something, please feel free to do so.

Regis
06-13-2005, 08:49 AM
Wrapping it up...

Mr. Widget
06-13-2005, 11:31 AM
Nice documentation.:)

I am butting in on this thread as these threads are read by many seeking advice and I wouldn't want others to come along and get the wrong idea...


You will notice immediately that the diaphragm only goes halfway down the pins and doesn't seat. This is normal, as JBL held this to a very tight tolerance and the bottom half of the locating pins is actually a press fit.

This is not true. I am not a professional reconer and would prefer if one of our forum members who is pop in here with advice, but I have done a few 2420/LE85s and a few 2441s and they range from so tight you have to drill out the guide pin holes to fairly sloppy. The diaphragm replacement should always be done with a sweep tone so that you can guarantee that there is no buzzing.

I think in the case Regis is documenting they were lucky that they were able to get a snug fit that wasn't misaligned.

Widget

Earl K
06-13-2005, 11:33 AM
For the Record ( & perhaps it's just MO ), I also don't mean to offend but ;

#(1) I consider it a significant & major no-no :no: :no: :no: to suggest that the floor is a suitable work-bench for a diaphragm replacement .

- Your posted pics "telegraph" this message that "work-bench location" is unimportant.
- I strongly disagree that work-location is unimportant for this sort of work - as will any professional reconer .
- Again, The floor is not a suitable workbench !

#(2) Your omission from mentioning that you cleaned the gaps of your le85s' (ie ; using masking tape wrapped around thin/stiff cardboard ) suggests to me that you aren't aware of this critical cleaning step .

- FWIW, metallic derbis ( from the air / floor ) needs to be removed ( from the work-area & the gap of the driver-piece being worked on ) before replacing an old diaphragm or installing a new diaphragm or recone . Thankfully, some-one in your household does a bang-up job at vacuuming. :yes: :yes: :yes:

#(3) Humbly , I mention that I'd prefer to see you change the title on this thread to something incorporating or suggested by some of these words ; the L300s & the "easy & proper" Horn-Removal /Re-installation .

- FWIW ( & IMHO ); That's where the greatest worth of the included pictorials lay .

:cheers:

Regis
06-13-2005, 12:00 PM
...by both Mr. Widget and Earl K. This is why I enjoy posting, because other members can add great info and advice to this thread. I guess we were lucky and there were no problems. I did test the first driver before installing it and it worked so well, that we wrapped it up and tested the second one in the cab. Though if there was an obvious problem, we would've had to pull the LE-85 out and redo it.

Earl K is right about the work space. I don't have a workbench where I'm staying (though the kitchen table would've worked) and we did perform this on the floor (though it is vacuumed with great regularity by a king-sized 50 pound self propelled chrome Kirby vacuum cleaner) and I checked the areacarefully (as noted) for what we call in the aerospace industry as FOD (Foreign Object Debris) before putting the cap back on. Thanks for the great input.

edgewound
06-13-2005, 02:20 PM
Please, EarlK, don't delete...that was excellent.:applaud:

Regis...I'm curious...did your diaphragm supplier inform you of the warranty disclaimer enclosed with your $244.00 part? No warranty when consumer installed due to tight tolerances, procedures, etc.

I'll just talk about the re-diaphragm. FYI...the RED terminal is NEGATIVE, black is positive. And this is addressed inside the crossover network. You really must have a debris-free work surface, a lighted bench magnifier, sweep generator and various other tools to make sure the new part fits properly...so many little things can go astray that will make your gennie part useless.

#1. You gotta clean the gap...and the slits in the phase plug....and the driver throat. Bits of dirt, metal chips, voice coil former residue...anything....MUST be cleaned out of the gap. Use 1" masking tape adhesive-side out folded outside of some card stock to dig into the gap. When the tape comes out clean after several times around the gap, then clean the gap again with some coffee filter paper dipped in acetone to clean out any tape adhesive bits left behind. Inspect the gap with a lighted magnifier to make sure it's CLEAN...there's only a few thousandths of an inch tolerance on either side of the voice coil when it's immersed in the gap, so this step is critical!...or you'll risk early mortality of the voice coil.

#2. Check the gap width uniformity with a gap guage (.031" on most 1" throat drivers) to make sure the top plate or phase plug hasn't shifted slightly. Alnico drivers can shift a little. The newer ceramic drivers are glued together...so any misaligned gaps are probably factory defects, which is rare...or it was dropped and broke loose. If you get adventurous and take apart an Alnico driver, the magnet will discharge, and subsequently need recharging.

#3. Clean the gap....again. Possibly metal chips from checking the gap tolerance found their way in.

#4. Inspect the new diaphragm. Check for high voice coil windings, check for roundness...sometimes they're not, right out of the box, and the consumer has not much recourse, because when the part leaves my shop in the box, I have no idea what went on from there...read the enclosed disclaimer...and the guy who put it in, NEVER does anything incorrectly...his dog ate it:bs:

#5. Trial fit the new diaphragm. Locating-pin holes are not always the same size as the locating pins. The diaphragm should fit snug on the pins but shouldn't need to be forced into place. If that's the case, the locating-pin holes need to be reamed out a bit....newer ceramic units have a relief machined into the top plate that the diaphragm drops into.

#6. Install the three diaphragm mounting screws...loosely....don't tighten down yet...just enough to hold down the mounting ring. Apply 3.5 volts(for 16 ohm, 2.83 for 8 ohm) test sweep tone from 500-1200Hz, and listen for any buzzing. Sometimes the diaphragm must be adjusted slightly to eliminate all buzzes. It's a good measure of thoroughness to sweep beyond the test frequency to ensure clean travel to lower frequencies, and adjust out any higher frequency anomalies. After all, these are always getting more program than the test frequencies...it's good to be thorough. Snug down the screws when it sounds clean and buzz and resonance free, while sweeping with test tone. BTW...polarity on the sweep test does not matter.

#7. Check the condition of the foam pad inside the loading cap. Get a replacement if its rotten. Check the condition of the lead wires. Make sure there are no short circuits to the loading cap from the outside spring terminals to the inner lead wires. Connect the lead wires to the properly colored terminals. Make sure the wires are lined up with the correct terminal. You don't want to twist and criss cross the wires when reinstalling the loading cap....cap needs to fit airtight. RED is NEGATIVE, BLACK is POSITIVE...yes that's right, it's backwards from what you're used to. Polarity conventions have been changing in the last few years to standardize with other mfr's products.

#8. Re-install the loading cap. Make sure it seats fully down to the top plate with no airleaks and the lead wires aren't resting on the diapragm dome...that doesn't sound good.

#9. Do a final thorough sweep test to the fully reassembled driver to makes sure it's good to go.

#10. It's cheap insurance to have the JBL Authorized servicer do the replacement. If the diaphragm fails due to user installation error....you're pretty much on your own.

Thanks...hope I covered everything:) ,

Edgewound

Mr. Widget
06-13-2005, 02:28 PM
Thanks for the thorough discourse... that is exactly what I was hoping for. I haven't had the privilege of taking the JBL course, but by trial and error I have discovered the 500-1200Hz sweeping is necessary.



#10. It's cheap insurance to have the JBL Authorized servicer do the replacement. If the diaphragm fails due to user installation error....you're pretty much on your own.

I absolutely agree! While I can and have done it... if something goes wrong... and shit happens, it is so nice to have it be someone else's problem and have the JBL warranty.

Widget

Regis
06-13-2005, 02:49 PM
I hear what you're saying, yes, I wish I had a lighted workbench, a cleanroom to make my own IC's, etc, etc. But I do own a lamp and magnifier and have some tools. Maybe I'm a lucky sumabitch, but it works fine, sounds good and Dave from NY prepped the motors before sending them (he had removed the diaphragms before sending them out). (I traded the original wax sealed, unopened LE-85's for a pair of undiaphragmed, perfect LE-85's. Add new 16421's and I'm in business.

Maybe I should've called this the "garage-grunge" thread :D . Just didn't seem as absolutely difficult as what it's made out to be (call it luck). As far as the schematic I looked at an L-300 and a 3133 schematic and unless it's wrong, the black negative input goes to the black wire. Please correct me if I'm wrong.

edgewound
06-13-2005, 03:33 PM
Hi Regis...

On Vintage JBL with the exception of the D123,for not-well-known reasons, positive voltage applied to the BLACK terminal will result in outward cone movement, and also diaphragm movement toward the phase-plug of JBL compression drivers. Check this with a flashlight battery and you'll discover this. As long as all network wires, go to the proper colored terminals, all is fine inside the enclosure...but it's backwards outside at the system input. Really, the only time this might be a problem, is if you're using other mfr's speakers in the same room...say for home theater. If this is the case, your fronts and rears will be out of phase....Please correct me if I'm wrong, and I'll research it further.

It wasn't my purpose to offend you in any way, and If I did, I apologize. I posted the rediaphragm process at the request of Mr. Widget.

I don't recall stating that you need a "clean room" to do this procedure, and you also didn't mention that the drivers were were exchanged and prepped by a Pro. Too much info is omitted in these forums....due to brevity... and can result in bad communication:( . But your thread was nicely done with the photos:) ...but some critical steps weren't mentioned.

Rock on up to the Summit,

Edgewound

Regis
06-13-2005, 03:46 PM
I just have to have some fun with this! Heck, I learned some new stuff from this, especially the out-of-round diaphragm condition that can sometimes occur. Just being humorously sarcastic. The thread was good in that it brought into play a whole lot of information (that unless I didn't search correctly) wasn't available before on this site. So I went with what Steve and I knew.

Thanks to all of you for your thoughts and input. And don't freak on the next thread upcoming, the L-300 bypass cap mod, as I worked on the floor (on a clean piece of large cardboard mind you)! I didn't remove the entire network as I would've had to pull the foilcals and then the L-pads off and then remove the horn again (the wires were at 3 PM next to thw wood brace, so getting to them would've been really tough).

I simply pulled the red and black wires from the inside of the speaker inputs and then removed the top screen, pulling it off and getting some slack in the the two harnesses (they were smart enough to make the wire harness's able to pull out the side of the screen) pulled the metal shoebox forward till it came out of da' woofer hole (that's the big hole at the bottom :D ) and propped it on a Digi-Key cardboard box. Pics and threads of the garage series of L-300 mods to come. And yes, they sound awesome bypassed! Details to follow! It wasn't easy mind you, figuring it out, but I believe I did and I'm happy with the results.

Regis
06-13-2005, 04:43 PM
Thanks Giskard, it's a good thing FoMoCo didn't make it confidential for Autozone to sell me auto parts! Otherwise, I would've never got that fuel pump/radiator/idle bypass valve or computer. And I did it on the driveway too!:D

57BELAIRE
06-14-2005, 08:03 AM
Hi Regis...

On Vintage JBL with the exception of the D123,for not-well-known reasons, positive voltage applied to the BLACK terminal will result in outward cone movement, and also diaphragm movement toward the phase-plug of JBL compression drivers. Check this with a flashlight battery and you'll discover this. As long as all network wires, go to the proper colored terminals, all is fine inside the enclosure...but it's backwards outside at the system input. Really, the only time this might be a problem, is if you're using other mfr's speakers in the same room...say for home theater. If this is the case, your fronts and rears will be out of phase....Please correct me if I'm wrong, and I'll research it further.

It wasn't my purpose to offend you in any way, and If I did, I apologize. I posted the rediaphragm process at the request of Mr. Widget.

I don't recall stating that you need a "clean room" to do this procedure, and you also didn't mention that the drivers were were exchanged and prepped by a Pro. Too much info is omitted in these forums....due to brevity... and can result in bad communication:( . But your thread was nicely done with the photos:) ...but some critical steps weren't mentioned.

Rock on up to the Summit,

Edgewound


Am I missing something here? I've always subscribed to the theory that....red/green = pos. and black = neg. :blink:

Zilch
06-15-2005, 12:52 AM
Am I missing something here? I've always subscribed to the theory that....red/green = pos. and black = neg. :blink:Yes. It's not polarity, rather, phase convention, and JBL, for the most part, uses one opposite what the rest of the industry does, except on SR stuff, which it wires backwards, and selected "anomalous" drivers.

Search the forum. There's reams of info on it here.... :D

edgewound
06-23-2005, 12:20 AM
Actually, it is Polarity Convention.

See this link from JBL :

http://www.jblpro.com/pub/technote/tn_v1n12b.pdf

Thanks,
Edgewound

Figge
06-23-2005, 02:06 AM
i did this on my 4430:s exacly the way regis did! only diffrence was that i did it alone since the horns are very easy to "pull" on that model, used the floor as working bench, worked out great! i did however not have those 2 pins to "steer it right" so i had to use a tone generator to get it right.