LE85 Problem...Help Wanted.

[Beowulf57]

Recently, one channel of my system began to sound a bit wrong: loss of clarity, a bit of coarseness, but hard to define. Music just wasn't "singing sweetly" anymore. Placing my ear right at the Diffusing lens (LE85 + HL92 horn) I could hear what sounded a bit like Harmonic distortion or perhaps Intermodulation distortion surrounding the notes from female voice and piano. This was masked when multiple instruments were playing and difficult to separate out of the sound when listening at a distance.

I commenced my troubleshooting run: checked different sources, different preamps, cleaned cable connections and tube pins sockets, swapped the mono-block amps left and right...nope, problem still there and only in the right channel speaker. Okay, crossover or driver problem. I connected a spare 2420 in place of the LE85 in the problem channel...problem disappeared.

I replaced the problem LE85 with the 2420 and the whole sound was right again...sweet, pure, great transient attack, clean and much better stereo soundstage. Night and Day improvement. Funny how tricky it is to identify a problem like this one.

So, my LE85 has a problem. It is about 35 years old (as are my 2420 spares) and never opened. So, a bit of advice please. Is this diaphragm replacement time? Or perhaps the phase plug is out of alignment? Should I run a sweep on the LE85 with a sinewave generator?

Any thoughts will be much appreciated.

Beowulf57...a.k.a. Douglas

[jcrobso]

I doubt that the phase plug is out of alignment, unless the driver has been dropped.
If you get strange noises on the frequency sweep, then it would be time to open it up and inspect the diaphragm. They are easy to replace just be VERY CAREFUL when you do it. If there are any cracks in the diaphragm or the surround it it time for a new one.

[yggdrasil]

Hi Douglas.

You need to open the driver and check(take off the back-cap):
* Beware of the strong magnetic field. Two hands on the screwdriver or a non-magnetic one.
* the leads for corrosion and if they are tightened properly
* the diaphragm for any visual damage
* if the foam in the back-cap has come loose and is in contact with the diaphragm

If you find and correct any of these possibilities you need to mount the back-cap and run a test.

The next would be to remove the diapragm and clean the gap before running another test. Remember to mark the position of the diaphragm. When mounting the diaphragm again you should be aware that the diaphragm can be moved slightly within the gap and that this alters the drivers response. A measurement microphone is nice for this operation to ensure optimal placement of the diaphragm.

If all of this fails, my guess would be new diaphragms.

Johnny

[Beowulf57]

Many thanks to you both...I'll open and inspect for problems and then run a frequency sweep test if I find any that are correctable. Further report to follow...

[Beowulf57]

When I ran a frequency sweep the only anomaly I noticed was a high frequency artifact sweeping between 600Hz and 700Hz. This added tone might have been around 10KHz, but that's just a earball value. Below that range or above, the sound was clean. This HF artifact did not show up when I swept my other 2420.

I opened up the back of the driver and cleaned the contacts...there did appear to be some corrosion and also bits of the foam were stuck to the screws. I carefully blew any detritus out from around the diaphragm. The picture shows a tiny bit of corroded material had adhered to the surround of the diaphragm: look just to the right of the lower left screw and you can see a few tiny spots on one of the triangular surround sections. I scraped this off with a plastic screwdriver. In any case the anomaly is still present and I doubt that tiny bit of material could have accounted for the problem in any case.

The foam is old and retains any compression, but it isn't crumbling away.

Next? Open the back up again and clean the gap?

[Robh3606]

Well one thing you could do is backlight the diaphragm and look for cracks/light leakage/at the edges of the compliance. There could be fractures there that are not easily seen but may show up in the impedance or F/R plots.

Rob

[herki the cat]

So, my LE85 has a problem. It is about 35 years old (as are my 2420 spares) and never opened. So, a bit of advice please. Is this diaphragm replacement time? Or perhaps the phase plug is out of alignment? Should I run a sweep on the LE85 with a sinewave generator?

Any thoughts will be much appreciated.

Beowulf57...a.k.a. Douglas

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With due respect to everyone helping, I suggest you should not touch any part of that priceless LE-85. Consult with JBL repair dept on how to package that driver for shipping and return it JBL for repairs.

Replacement diaphragm is identical for 2410, 2420, LE-175, Le-85 & are no longer made by JBL except on special order to "Orange County Speakers" which they will special order for you at some $820.00, The last JBL replacements cost approx $240.

That driver is like a fine watch and JBL can clean the delicate structure, and remagnetize the motor, and maybe even save the diaphragm if it has not been over-dirven to the point the where the aluminum has work hardened to end of life.

I would think that since JBL can make a single diaphragm or two for Orange County Speakers, they can make one for you on a repair basis. The repaired Le-85 will come back like new.

Think of this issue in terms of [quote= is the entire speaker system worth $820?]
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Cheers herki the cat

[Mike Caldwell]

You may try just cracking the diaphragm screws loose enough to slightly move the diaphragm, then apply you 600hz tone while shifting the diaphragm. You will not beable to move it much but it does not take too much movement to make a difference. Having the diaphragm screws evenly tightened can make a difference as well. DO NOT use a screw driver that has the removable bits!!!! The magnet can suck then out of the screw driver and into the diaphragm......and your diaphragm is next to imposable find in an original JBL replacement.

[Beowulf57]

Thanks Rob, Mike and herki.

I will try the slight shifting of diaphragm position first...one question when I apply the 600-700HZ tone, is it necessary for the horn to be attached to the LE85 for correct loading?

Next if that doesn't help I'll try the backlight check for cracks and also check the gap for detritus.

Finally, thanks herki (yes my system is worth far more than $820) but I've been working on these speaker systems for over 30 years and have repaired a number of drivers...so I'm going to give this my best shot.

Repairing the aluminum dome on a D131 was the most fun: I used pliobond and a q-tip stick to gently pull a crushed area back out to true round and then acetone with q-tips to remove the pliobond. Worked like a charm.

[Mike Caldwell]

For the tone test you do not need the horn on the driver, if there is a crack in the surround it will be very apparent with a test tone. Do you have a sweepable tone generator or one with fixed frequencies. You want to drive the driver with a enough level for some output but not deafining! I would go down to around 500hz for a low freq. and out to as high as you can hear for a test sweep.

[Beowulf57]

For the tone test you do not need the horn on the driver, if there is a crack in the surround it will be very apparent with a test tone. Do you have a sweepable tone generator or one with fixed frequencies. You want to drive the driver with a enough level for some output but not deafining! I would go down to around 500hz for a low freq. and out to as high as you can hear for a test sweep.

Yes, I can sweep from 500HZ to beyond my hearing ability (14-15KHz). Around 2.5VAC seems plenty loud to me...I'll run the check and report back. And just to confirm: no problem running the sweep test with the back plate off? Thanks for the advice.

[Mike Caldwell]

You'll need the back cover off to do the test during the tone. I would start at a lower frequency and then move the diaphragm while listening. You'll hear when you find the sweet spot. I'm almost certain that your drivers will have guide pins for the diaphragm so you may not get much movement, sometime it a matter of slight flexing and tightening of the screws. Now here is a trick to proceed with CAUTION or maybe a more expendable diaphragm to experiment with! You can enlarge the guide pin holes on the underside of diaphragm mounting ring with the next size larger drill bit. That will give you a larger range to tweak the diaphragm in.

[Beowulf57]

Many thanks Mike...I'll report back.

[Beowulf57]

I have resolved the problem...it turned out that by simply cleaning all connections to the diaphragm as well as the bit of corrosion stuck to it and a few particles floating around in the neighborhood, the distortion disappeared.

I had a bit of a laugh at myself after I noticed some odd sounds from the driver during the frequency sweep test with my EICO 379...worried that it was a driver damage problem until I realized that a 600 ohm output impedance audio signal generator does not like driving an 8 ohm load! Set up properly with a small solid state amp/N1200 crossover, the test sweep was identical for my LE85 and my other 2420.

Now, I don't think I'll bother replacing the 2420 I installed in place of the LE85 while I was troubleshooting...takes about 2 hours and the two sound identical to my ears (identical diaphragms). So on the shelf with the LE85 and back to enjoying listening.

Thanks to all for your help and to Mike in particular. Happy New Year!

Beouwlf57, a.k.a. Douglas

[Mr. Widget]

I have resolved the problem...it turned out that by simply cleaning all connections to the diaphragm as well as the bit of corrosion stuck to it and a few particles floating around in the neighborhood, the distortion disappeared.

Ah, the ravages of time.

We take it for granted that since these older drivers were designed to last forever, that they will... and if they aren't abused they can, but some maintenance and care are required.

Congratulations!


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