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Thread: 120 Ti Midrange Failure

  1. #1
    Member Vintage Nut's Avatar
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    120 Ti Midrange Failure

    One of the midrange drivers in my pair of 120ti speakers has died. Sucks 'cause it was the one of the two that had a perfect dome - lol. Anyway, I think the crossover may be damaged too, because when I swapped the 104h-1 drivers between left and right to test them, the good one only works in it's original cabinet. I'm not sure how to test the crossovers aside from hooking a speaker up to them. I don't even know how to test the drivers properly with a hand-held tester. The bad 104h-1 does make a little noise, but it's barely audible. Anyway, I guess my question is how do I test the crossover before I start looking to replace it? And how do I test drivers? I do have a multi-meter tester.

    Also, if I decide to run a pair of 104h-2 drivers, as they are more readily available, would they sound good? I've had the 120 Ti speakers since new in 1990 and have ALWAYS LOVED them.
    Sony N55ES (2), E1000ESD, C85ES - JBL 120Ti | Onkyo TX-SR605 - JBL L830 (4), LC1 (1) | Dell - Pioneer SX-750 - JBL 4406

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    Member Vintage Nut's Avatar
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    Just to quickly clarify, the bad 104h-1 does NOT work (aside from faint sounds) in either cabinet. Only the good 104h-1 works in the cabinet it came in.
    Sony N55ES (2), E1000ESD, C85ES - JBL 120Ti | Onkyo TX-SR605 - JBL L830 (4), LC1 (1) | Dell - Pioneer SX-750 - JBL 4406

  3. #3
    Senior Member rdgrimes's Avatar
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    Have you tried checking DC resistance on the bad driver? The 104 should read 3.8-4.6 ohms.

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    Just tested: 1.0 on bad driver and 4.4 on good driver. Is that something that can be repaired or should I just replace it?

    Also figure mr crossover is bad. How do I test it with a meter and can it (normally) be repaired?
    Sony N55ES (2), E1000ESD, C85ES - JBL 120Ti | Onkyo TX-SR605 - JBL L830 (4), LC1 (1) | Dell - Pioneer SX-750 - JBL 4406

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    Probably easier to replace. there are a few on ebay now for a reasonable price.

    Allan

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    Senior Member rdgrimes's Avatar
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    Quote Originally Posted by Vintage Nut View Post
    Just tested: 1.0 on bad driver and 4.4 on good driver. Is that something that can be repaired or should I just replace it?

    Also figure mr crossover is bad. How do I test it with a meter and can it (normally) be repaired?
    Given the 1u measurement, it's possible that something in the XO got cooked. Yes that can be repaired. A visual inspection of the mid-freq components in the XO may reveal something. Schematic is HERE.

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    Member tarior's Avatar
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    Fortunately, the 104H is rebuildable.

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    Quote Originally Posted by rdgrimes View Post
    Given the 1u measurement, it's possible that something in the XO got cooked. Yes that can be repaired. A visual inspection of the mid-freq components in the XO may reveal something. Schematic is HERE.
    Thanks for the help. Here's a shot of the N120 XO. My eye is not trained to see anything wrong, other than the brownish coloring on one of the white blocks. But, it looks to me like that block is actually connected to the 044ti tweeter. Can I test things with the multimeter? Maybe I'll just find a replacement.

    http://i922.photobucket.com/albums/a...0/20022c1c.jpg
    Sony N55ES (2), E1000ESD, C85ES - JBL 120Ti | Onkyo TX-SR605 - JBL L830 (4), LC1 (1) | Dell - Pioneer SX-750 - JBL 4406

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    Quote Originally Posted by tarior View Post
    Fortunately, the 104H is rebuildable.
    I wonder if Orange County does them. They did a fine job refoaming the woofers a few years ago.
    Sony N55ES (2), E1000ESD, C85ES - JBL 120Ti | Onkyo TX-SR605 - JBL L830 (4), LC1 (1) | Dell - Pioneer SX-750 - JBL 4406

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    Member tarior's Avatar
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    I can rebuild them, too.

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    Senior Member rdgrimes's Avatar
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    Quote Originally Posted by Vintage Nut View Post
    I wonder if Orange County does them. They did a fine job refoaming the woofers a few years ago.
    $95
    http://www.speakerrepair.com/ocsrepairprice.html

    I'd give the XO to a qualified technician, should be cheap to fix.
    Might as well take this as an excuse to have both XOs re-capped.

    The resistor on the far right looks suspicious to me.

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    Senior Member DavidF's Avatar
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    Quote Originally Posted by Vintage Nut View Post
    Thanks for the help. Here's a shot of the N120 XO. My eye is not trained to see anything wrong, other than the brownish coloring on one of the white blocks. But, it looks to me like that block is actually connected to the 044ti tweeter. Can I test things with the multimeter? Maybe I'll just find a replacement.

    http://i922.photobucket.com/albums/a...0/20022c1c.jpg
    The resistor (white blocks) that has the discoloration is R2 or the 2.4 ohm resistor in the schematic from my look at the picture. Could be wrong but this seems to feed through the 12 mF Cap, into the coil then the resitor in question.

    If that is so then this one component is suspect. How then did enough power to bleed through to the mid range (guessing that indeed the former on the mid has distorted from heat but not quite blown)?
    David F
    San Jose

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    Thanks for the pointers, guys. I don't have much technical knowledge on how to do this stuff myself, so will contact Orange County tomorrow as they treated me well last time.
    Sony N55ES (2), E1000ESD, C85ES - JBL 120Ti | Onkyo TX-SR605 - JBL L830 (4), LC1 (1) | Dell - Pioneer SX-750 - JBL 4406

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    Quote Originally Posted by tarior View Post
    I can rebuild them, too.
    Do you have JBL re-cone kits for this? Orange County Speaker is telling me there are no more available from JBL. I want the same stuff that JBL put in them, not 104H-2 parts.
    Sony N55ES (2), E1000ESD, C85ES - JBL 120Ti | Onkyo TX-SR605 - JBL L830 (4), LC1 (1) | Dell - Pioneer SX-750 - JBL 4406

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    Member tarior's Avatar
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    Quote Originally Posted by Vintage Nut View Post
    Do you have JBL re-cone kits for this? Orange County Speaker is telling me there are no more available from JBL. I want the same stuff that JBL put in them, not 104H-2 parts.
    As far as I'm concerned, JBL cone kits haven't been worth the $$ for some time. The ones that are available (at least the ones I've seen and spent the big bucks on) are put together in Mexico from the same off the shelf aftermarket parts that all of the generic reconers use. If I can't get the exact cone, I will reuse your cone and just replace the coil and spider. I do it all the time to preserve Aquaplas coated cones, as many of those are discontinued now as well.

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