View Full Version : 2404H Repair

09-03-2003, 11:44 AM
I need to replace the diaphragm of an 2404H.
Can someone explain me how to proceed ?
( in English, German or French )
Many thanks in advance.

09-03-2003, 12:22 PM
Ok but I am not a JBL TRAINED technician. If I were you and have the diaphrams and a JBL tech close use him. All you do is remove the four hex head bolts right under the horn. This will remove the entire horn assembly and expose the diaphram. There is a triangular cone/phase plug. The phase plug holds the center of the diaphram assembly in place. To remove the phase plug you remove the label to expose a screw that goes through the pole piece and holds the plug. When you remove the plug do not let it spin. Hold it fast and turn the screw only. If the plug spins it can tear the diaphram and jam the voice coil. Once the plug is off you can unsolder the old diaphram and install the new. Thats as much as I know. I don't know if the diaprhrams a self aligning or if you need a tech with test equipment to really do it right. So think hard before you start. There are others here that know a lot more than me that I am sure will chime in. Attached is a photo of a 2405/077 without the horn shell to give you an idea what it will look like. Just substitute clear acrylic for solid aluminum phase plug and us course this is alnico.

Good Luck Rob:)

Alex Lancaster
09-03-2003, 12:39 PM
The diaph has holes for centering pins, but check the centering of the gap; if OK, air blow the gap, clean it with masking tape (folded sticky sides out) around a business card, and wipe it all around, if the coil burned, use solvent, MEK or paint thinner, to remove the gum residue.


09-03-2003, 12:43 PM
from robh
I don't know if the diaphrams a self aligning or if you need a tech with test equipment to really do it right. They are not self centering, and need prper alignment.

From a journeyman JBL technician... (you know who you are ;) )

I'll not offer attribution unless given the OK, and also will delete if requested. So, pay attention, boys..., this might be brief! :scold:


1. Check unit for damage (cracked throat, shifted top plate, etc.) Remove front cover and old diaphragm assembly. On ring radiators, remove inner cone and outer horns and unsolder old diaphragm.
2. Using gap gauge, check gap for size and alignment.
3. On 2-inch throat drivers, tap on top phasing plug. The unit should make a solid sound. A “hollow” or “clicking” sound indicates a loose phasing plug.

1. Fold piece of masking tape lengthwise around cardboard digger with adhesive side exposed. Insert in gap and rotate to clean out debris. Continue cleaning until tape is clean when withdrawn. Inspect visually with magnifying light.
2. Inspect new diaphragm for damage. Line up holes in diaphragm to mounting pins on driver. Carefully lower assembly into place. Replace diaphragm mounting screws. On ring radiators, solder leads to terminals.
3. On drivers, hook unit up to oscillator set to 3-4 volts at proper frequency (550Hz on 1-inch drivers, 350 Hz on 2-inch drivers). Listen for buzzing. Use a small mallet to tap lightly on side of diaphragm frame until centered in gap and buzzing ceases. Tighten down diaphragm mounting screws.
4. Reconnect terminal leads onto diaphragm assembly and replace cover. On ring radiators, replace inner and outer horn.
5. Perform final sound test.

09-03-2003, 12:43 PM
Hi Rob
Many thanks for your advice.
I havent found the screw behind the label ! ! ! !
I replaced the diaphragm with an used one for test.
It works. I will have the new diaphragms in 10 days.
Merci beaucoup

09-07-2003, 12:17 AM
If you are not using non-magnetic tools around compression drivers, keep a firm and controlling grip on the tools. On small units like the 2405, 2404, etc., make sure the driver cannot pull itself to the tool. I use a piece of heavy-ish box cardboard about 12" square, with a hole that fits around the driver part being worked on snugly. A dictionary on either side of driver or driver part to hold the cardboard fast works fine. Use whatever works for you, but be sure neither tool nor driver can make unexpected movements. AND, if it happens, it will do so VERY quickly, most likely damaging a diaphram, before you even know it!!
Those are some mighty high magnetic flux levels present!
Robb, right on with the "NO-SPIN" advice. I've seen way more than one brand new ($85 or more?) 2402 etc. diaphram reduced to pricey aluminum foil, due to that itty-bitty detail being ignored.