Jbl 250ti urgent help needed

[dj7675]

I just was received a beautiful pair of jbl 250ti. They were completely restored/upgraded from jbl L250 to the ti version not long ago. I had them shipped via uShip and they arrived in gtpreat condition. However, one tweeter is not working. I'm hoping it's something simple but am hoping for some guidance on where to start. I started by attempting to remove back panel behind tweeter. I removed the screws, but can't seem to get the panel off. Is this a good place to start and if so how do I get the panel off? Other thoughts?
Thanks!
Darin

[kelossus]

Yes taking the tweeter access panel off is the first step.

I used a suction cup to pull the panel off as it was bonded fairly tight to the gasket.

[edgewound]

I just was received a beautiful pair of jbl 250ti. They were completely restored/upgraded from jbl L250 to the ti version not long ago. I had them shipped via uShip and they arrived in gtpreat condition. However, one tweeter is not working. I'm hoping it's something simple but am hoping for some guidance on where to start. I started by attempting to remove back panel behind tweeter. I removed the screws, but can't seem to get the panel off. Is this a good place to start and if so how do I get the panel off? Other thoughts?
Thanks!
Darin

Check the jumper straps on the crossover connections at the bottom rear of the enclosure to make sure all the straps are there and tight. It's a good idea to clean all those screws with a wire brush...or replace them.

Use a putty knife or a glazier's knife to dislodge the stuck back panel. Go around the gap and gently pry it loose. Often-times the paint is not fully dry during assembly and ends up gluing the panel in place. Firstly...make sure the tweeter is actually connected to the crossover network. If you have a meter that measures AC voltage, you can check to see if any signal is present at the crossover output. Another way to check it is to connect another small speaker...if you have one handy...and see if it's live.

Your 044ti tweeter issue might be the foam plug under the dome has rotted and migrated into the voice coil gap. The foam rots and turns to goo which can severly degrade the output, possibly leading to voice coil failure from over heating. The tweeter must be disassembled, cleaned of all rotten foam and a new foam plug installed. It's a challenge to get the 044ti apart without damaging the diaphragm phenolic mounting plate. When you get the tweeter removed check the voice coil for continuity. DC resistance should be in the 3.6-4.4 ohms range. Another possibility for damage is a shifted magnet assembly that has clamped the voice coil in place rendering it paralyzed. Sometimes the voice coil will survive this and very careful disassembly and repair can save the tweeter, since replacement diaphragms are no longer available.

Good luck in your pursuit! Call me if you should need additional guidance.

Ken

909-946-5944

[rdgrimes]

Removing that back panel can be a BEAR, especially if its never been off. Heat is a good tool to have in the mix, since the gasket is a cheap foam that turns to goo over time. Worse case, put a few large wood screws into the holes to grip the cover, then gently rock it loose. You might even need to make some long bars and shims with the wood screws going through to use the screws to pull the cover as you tighten them - like a big gear puller. Patience and creativity here, you do not want to break the cover.

[kelossus]

I still think the suction cap method has the potential for the least amount of damage, none. The finish of the rear of the cabinet is matte and smooth, perfect for a suction cup.

[dj7675]

First off thank you for all who replied. After working on removing the back and couldn't get it off through several methods, I decided to test it again, and to my dismay, the tweeter was working fine. I don't know what happened or why but it appears to be working perfectly now. I will definitely keep monitoring it, and if I need to get the panel off I will have a few more ideas to try. Thanks again to all who replied. Wow do these sound great.