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Thread: L Pad removal

  1. #1
    roundnyellow
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    L Pad removal

    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

  2. #2
    Senior Señor boputnam's Avatar
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    Hey...

    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

    Let us know how you go...
    bo

    "Indeed, not!!"

  3. #3
    roundnyellow
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    Thanks for the thread, lots of good info. One more question, how do I sneak the hair dryer past the wife? I’m working on a set of L212’s and their foilcals are sure enough pretty. Oh well, here I go.

  4. #4
    roundnyellow
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    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.

    much thanks,
    Gary

  5. #5
    Senior Señor boputnam's Avatar
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    Thumbs up

    Nice!

    You have avoided the damage most inflict. Don't forget to return the hair dryer...
    bo

    "Indeed, not!!"

  6. #6
    roundnyellow
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    not the pads

    Should have jumpered the pads first because they still don’t work. Is it generally the series components that go? In High circuitry C2 and mid circuitry C1, L2 or R2/.

    Tx
    Gary

  7. #7
    Senior Señor boputnam's Avatar
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    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.
    bo

    "Indeed, not!!"

  8. #8
    Senior Señor boputnam's Avatar
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    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...

    Here it is: roundnyellow L212 Thread - Link

    So, if this is right, then Gary, tell us what you done thus far...
    bo

    "Indeed, not!!"

  9. #9
    roundnyellow
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    Good evening, yes they are L212’s.
    Let me see, so far I’ve;

    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.

    popup

  10. #10
    Senior Señor boputnam's Avatar
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    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

    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...
    Last edited by boputnam; 09-29-2003 at 09:58 PM.
    bo

    "Indeed, not!!"

  11. #11
    Senior Member Ian Mackenzie's Avatar
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    Okay,

    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.

    Ian


  12. #12
    Senior Member Don C's Avatar
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    Here's the L-212 techsheet
    Attached Images Attached Images

  13. #13
    Obsolete
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    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

    "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.

  14. #14
    roundnyellow
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    First, I’d like to thank everyone for the help. It’s 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 “infinite” 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.

    Gary

  15. #15
    Senior Señor boputnam's Avatar
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    Hey, Gary...

    I hate to be the one 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...
    bo

    "Indeed, not!!"

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