View Full Version : 2420 problem?

06-25-2003, 07:20 PM
On my JBL 4333's I have replaced l-pads on horns and tweeters. One horn will have a lower output until I rotate the l-pad to full volume and then turn the output up. The horn will sound intermittent for a moment then return to regular volume. I have tried to take it out of the cabinet, but the square metal cover on the back won't give. I'm in Vancouver, BC and am not sure if I can do this repair myself or seek the aid of a professional? Any ideas?



Tom Loizeaux
06-25-2003, 07:38 PM
To remove the 2420 from the 4333 you should probably remove the woofer so you can grab the horn and driver. The upper rear panel has an inner and outer ring of screws. Remove the outer set. This will free the cover panel. You can try to reach up inside the cabinet and tap the panel, or block of wood around the 2420, to dislodge it. Sometimes they are stuck in pretty tight. You could also remove the four large phillips head screws on the front around the 2312 horn. This will free the horn and give you something to push the rear panel out with. Be careful, the driver and horn are heavy, and still connected to the wiring harness!
However, from what you're describing, I'll guess that you simply need to clean the L pads!
With the woofer removed, reach in and, using a flashlight, find the two L pad cans. Spray a quality electronic pot cleaner into the slits on the rear of the can and promptly rotate the control all the way, back and forth a few times. Do one and then the other. This usually does the trick. It may need a second treatment if they were especially dirty. Check to see if these are working properly, even before re-installing the woofer.

Let us know.


06-25-2003, 07:49 PM
l-pads are brand new....only 4 weeks old. Can my solder job be faulty? What would I look for on the horn for problems? I have never worked on a horn before and am worried I could damage it. Lastly, I'm wondering if the problem could lie in the crossover?

Seems like I need to do some research...learning on speakers!!

scott fitlin
06-25-2003, 08:40 PM
the problem, from what your describing, is either your L pad or your xover. Its possible to have gotten a faulty l-pad.

From what your describing I would think that your L pad connections may be faulty and whats happening is at first the faulty connection isnt making connection, now when you turn the L pad up and boost the output your causing the faulty connection to arc, and then it completes its connection!

I had this years ago with a pot in a xover. same thing. At first no volume. Then turn the pot kinda high and push the volume, a second or two of intermittent signal, then it was on. And the xover was brand new! Service replaced that pot and no further problems!

06-26-2003, 12:02 AM
I had quite a similar problem with my 2421 drivers. The problem was, that the soldering joint on the voice coil end has become loose somehow. Resoldering solved my problem completely.



Tom Loizeaux
06-26-2003, 02:12 PM
The meathod for locating an intermittent or failed connection is to do a continuity test. This is done usually with a VOM meter in the lowest resistance (Ohm) setting. Put the meter points on either side of each connection in the chain until you find the faulty one. Usually re-soldering will solve the problem.
If this is beyond your skill level, have an electronic service person do it for you.
Let us know what ou find.


07-19-2003, 12:33 AM
Update on the intermittent driver. First off I resoldered the l-pad, no chage. Second is I figured out how to remove the horn from the cab, but am worried about damaging it, if I crack it open. I noticed red wax on the screws to the driver and I'm hesitant to open it, if the problem is in the crossover. Still same problem, at a low volume the output is uneven between left and right. When I crack the volume up, the horn will sputter between less and even output and eventually become even with the other??? I might have to pull it and get a pro to test it on a generator, perhaps have the crossover looked at.