View Full Version : L Pad removal
09-28-2003, 04:53 PM
Some help please.
I'm replacing the LPads on a set of JBL's. How do they come off?
Screw, pry? There's a plastic cover on the front panel identifying controls, does this come off? It seems to be glued on.
Thanks for you help
09-28-2003, 05:00 PM
Without surfing here to try and sus what cabinets you're working on, L-pads can be terrorizing, regardless.
The cover plate does come off - but it was not designed to do so. Best of luck!
L-pad Replacement - Link (http://www.audioheritage.org/vbulletin/showthread.php?s=&threadid=792)
Let us know how you go...
09-28-2003, 05:32 PM
Thanks for the thread, lots of good info. One more question, how do I sneak the hair dryer past the wife? Iím working on a set of L212ís and their foilcals are sure enough pretty. Oh well, here I go.
09-28-2003, 05:56 PM
It worked. Fired up the old Revlon 1875 did some prying with a steak knife and presto!! The foilcal hid three mounting screws. It was easy and no apparent damage done.
09-28-2003, 06:01 PM
You have avoided the damage most inflict. Don't forget to return the hair dryer... :rotfl:
09-28-2003, 09:31 PM
Should have jumpered the pads first because they still donít work. Is it generally the series components that go? In High circuitry C2 and mid circuitry C1, L2 or R2/.
09-29-2003, 12:13 PM
Originally posted by boputnam
"...Without surfing here to try and sus what cabinets you're working on..." Would certainly be helpful to know what you're working on, Gary. :confused:
09-29-2003, 12:26 PM
Originally posted by Giskard
Somewhere burried in this thread he said he was working on L212's? Yup. Good memory. I thought so too, but was too lazy to go find it... :banghead:
Here it is: roundnyellow L212 Thread - Link (http://www.audioheritage.org/vbulletin/showthread.php?s=&threadid=766&highlight=l212)
So, if this is right, then Gary, tell us what you done thus far... :yes:
09-29-2003, 06:21 PM
Good evening, yes they are L212ís.
Let me see, so far Iíve;
Woofers are out of both boxes for new surrounds.
Box 1, the 066 works fine
The mid does not work, new lPad nothing, jumpered Lpad still nothing. Put it in box 2 it works fine. I found a blob of resign in the bottom of the box.
Followed the same routine for Box 2 066, nothing. Mid works fine. Have an inductor hanging from the board. May have over heated and come loose.
09-29-2003, 08:55 PM
Originally posted by roundnyellow
Box 1, the 066 works fine. The mid does not work, new lPad nothing, jumpered Lpad still nothing. Put it in box 2 it works fine. So, the Box1-MF is good, but Box1-MF path is not good.
I found a blob of resign in the bottom of the box. Resin? Possibly goop from a capacitor? Uh-oh... Is this Box 1?? Guessing crossover is at least partially toast. Anybody have experience with this symptom...?
Followed the same routine for Box 2 066, nothing. Mid works fine. Have an inductor hanging from the board. May have over heated and come loose. Hey, Giskard - the kid needs a L212 schematic. I don't (think...) I have one. Can you help? If we can determine what that inductor is, it might be from the HF path, and replaceable remedying that :hmm:
Box1: So, if the Box1-066 works in Box2, the driver is OK, and HF portion of network OK. MF path not OK.
Box2: HF path not good. MF works fine. Another network problem...?
If Box2-066 works nowhere, it's toast.
Any idea if the network to the LF's (8-inch) work? What about the VLF (12-inch)?
The phrase: A VERY SPECIAL NETWORK careens around my brain...
Man we (er, me...) need a concise understanding of what works where, and when. This is murky.
popup And that, has me baffled...
09-29-2003, 10:21 PM
Would remove the networks from both boxes for testing.
Remove the mid coil L2 & R2 in Box (1) from the board and test for DC resistance if you have a multimeter or circuit tester (a simple meter and Tandy for $20 will do).
If either L 2 or R2 are open circuit then need to be replaced.
In Box (2) check the DCR of the 066 tweeter, if its very low (less than 1 ohms) the tweeters is fried, also check the L pad. (make sure the woofer wires are not shorting)
Let us know how you go.
09-29-2003, 10:40 PM
Here's the L-212 techsheet
09-30-2003, 07:24 AM
You will need to determine which L212 network you have.
I posted these schematics on another thread started by this same person concerning L212's:
L212 Schematics (http://www.audioheritage.org/vbulletin/attachment.php?postid=6158)
"Anybody have experience with this symptom...?"
"The phrase: A VERY SPECIAL NETWORK careens around my brain...
Man we (er, me...) need a concise understanding of what works where, and when. This is murky."
Yes, your Authorized JBL Service Center has all the required expertise to properly service JBL loudspeaker systems.
The Sevice Manual for the L212 is over 20 pages long. Perhaps Don could check to see if it can be added to the Library. Something tells me it's out of the question but stranger things do happen.
09-30-2003, 08:03 PM
First, Iíd like to thank everyone for the help. Itís very much appreciated.
Ian, I did the checks you suggested. R2 is open in box 1; this is the box that has the inop mid.
Box 2, DCR across 066 is ďinfiniteĒ open. The Lpad over heated at one time, its case is discolored and the surface coating is pealing off. Any suggestions for box 2?
Once again thanks for all the help.
09-30-2003, 08:17 PM
I hate to be the one :spchless: but with this extent of damage, you might be best thinking about a complete rebuild of the electrics, L-pad(s) and network(s). Whomever partied hard, toasted at least one 066, and that L-pad. No telling how much more damage there is. Not worth the sleuthing, me thinks.
Instead, I'd salvage the cosmetic pieces and start a dialogue with JBLPro about parts for the L212 schematic (which one...?). They will tell you what they don't have, and places like this Forum, and Parts Express can nurse you along.
Shameful waste, actually. But, the results will be well worth it. You handy at all with a soldering iron?
That's my ha'penny...
10-01-2003, 01:35 AM
I agree with Bo,
First up, decide if to want to use the expertise of a JBL auth service dealer, or order the parts and diy fix it.
No doubt the service agent will test and check everything including the mid cones and tweeters with a warranty( the coils may be seared but not shorted).
The 066 sounds like a service job but Giskard will no doubt clarify this matter.
If you care to do a diy repair on the crossovers and can handle a soldering Iron, the capacitors are propably okay, but I would tend to replace all the ceramic resisters and L pads.
Sounds like the previous owner overloaded the amp and clipped the output (playing Jimmi Hendricks) sending a large distorted HF signal into the speakers and smoked them.....imagine the smell, probably not as strong as the hooch they were on at the time..muhahhaahahh
10-01-2003, 05:32 AM
"The 066 sounds like a service job but Giskard will no doubt clarify this matter."
I have one 066 diaphragm left. JBL should have a few left. Once these are gone, the 066 is no longer serviceable. The LE5-9's were marked as "no longer serviceable" earlier this year but OCS or other Service Centers might have a kit or two left in stock. I used my very last LE5-9 kit the other day. The 112A's and 112H's will no longer be servceable once this last batch of recone kits are exhausted.
I'd recommend a complete rebuild of both networks and use the 58450 L-Pads instead of the stock 10285 L-Pads. I can supply the Parts Express equivalent part numbers if desired (I've posted them before, I just can't remember if it was this forum or a previous version, perhaps a search on 10285 or 58450 will turn them up).
What are the DCR values on all your drivers?
Do you have the means to do aural sweeps to test the drivers?
If you do then I can provide you with the necessary test frequency ranges and the schematic for the 066 test network.
I am currently working on building biased networks for my L212's and am trying to figure out how to make the whole mess fit in that tiny space :)
10-01-2003, 08:35 PM
Itís DIY or DOA whichever comes first!
I scavenged parts from the #2 board for use on the #1 board. Iíll smoke test the #1 board tomorrow evening and post the results.
Has there been a survey proving direct correlation between alcoholism and soldering?
Iíll leave you with a question. With so very few parts available for the 212 models when do they stop being 212ís and become just JBL boxes with various JBL parts?
10-02-2003, 01:51 AM
You'll find similar issues in other recent JBL renovation threads.
Has there been a survey proving direct correlation between alcoholism and soldering?
No thats a dangerous mix, only smoking an AA.
See what the remix of parts brings and if a 066 repair is possible.
If the answer is affirmative Will Robinson I would walk in Giskards footsteps, and if you care for the L 212's dearly and they will last another 20 years.
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