Grateful Dead Music Forum

A place to talk about the music of the Grateful Dead 

 #91364  by lunasparks
 Sat Dec 25, 2010 10:38 am
Apologies in advance if this is speakers 101, but I don't know much about the ins and outs.

Anyway, on of the K120s in my cab is not working right. I hooked it up alone to test it out and reveals the following: I can mostly only hear a little kind of distorted crackling, barely audible through it when trying to play some chords. THEN, all of a sudden it will open up and sound great, just like it's supposed to...and will scare the crap out of me with the surprise in volume. It may play okay for 20 seconds, maybe a minute or so before dying again, going back to barely audible if anything at all.

I don't think it's blown. Seems almost like a bad connection? I tried a different speaker wire, one I know is good, but same problem. I don't know what's wrong. :?

Could anyone offer some advice or possible diagnosis? Thanks!
 #91365  by Pete B.
 Sat Dec 25, 2010 1:49 pm
It may be something related to the connection terminals/posts.
You might poke around by the terminals, reseat the wires, etc.
I had a brand new JBL D120 recone (with a generic E kit) that failed in a similar intermittent manner on the 3rd or 4th song of a set because the isolation grometts on the terminal posts had somehow failed to do their job (they are like little ceramic washers).
I brought it back to JaMac here in Portland and the guy fixed it for free and was very apologetic like it was his mistake for not checking this during the recone.
It wasn't even my speaker... a friend wanted to sell it to me and I was just "checking it out" that night (I returned it to the guy).
 #91370  by lunasparks
 Sun Dec 26, 2010 7:41 am
Thanks, Pete. I fooled around with the wires but can't get anything to work consistently.

Would it make sense to get some contact cleaner (like a DeOxit or something) to spray in the push-down post holes? Alternatively, anybody know if it's possible somehow bypass the posts? I'd like to diagnose that it's the connection and not something more fundamentally wrong with the speaker. I can't seem to find anything in my web searches that discusses this kind of problem. It's killing me!
 #91688  by lunasparks
 Tue Jan 04, 2011 3:34 pm
So I'm guessing not a lot of speaker repair experts in these parts! 8)

Anyway, here's an update and a warning for fellow JBL fans. Thanks to some helpful dudes on the Lansing Heritage forums, I got it figured out that bad lead wires on the cone near the dust cap were the likely culprit. Local JBL repair only wanted to recone ($264!). After much searching I found a local guy to look at it. He determined it was the lead wires and I paid him $30 to fix it. He wanted to give the money back--I insisted he keep it as a token of goodwill--because he doesn't think his fix will last. Why?

Because the turd I bought the speaker from on ebay had apparently already done a prior fix, done a decent job of covering it up so I didn't notice. But when my guy got me to see how there was a larger, odd solder blob (which kind of ruined the lead wire and makes further repair almost impossible) on one of the leads that doesn't match any unmolested K120, I knew I'd been taken by an ebay scoundrel. Predictably, this douche sold it as all original, blah blah. Also, even though he only lives a few miles from me he wouldn't agree to local pickup (even at a neutral destination); I knew something was stinky right there.

Live and learn, I guess. But if you're not already being careful with ebay JBLs, I suggest you always take a really, really hard look. That's my PSA for the day. These bad boys are getting up there in age and there'll probably be more and more inscrutable folks out there trying to offload their questionable goods for top dollar...especially knowing what it costs for JBL recone kits these days. :shock: