JBL model 4627

[analogean]

Hello,
i have a pair of JBL 4627's ( the 4627, with a E145-8 and the 2901A High-Frequency Power Pack, a 2410 compression driver on the 2301 perforated-plate horn-lens with a high-pass network.) and I cannot hear anything out of the high frequency speakers.
I thought I would just take them apart and have a look inside to test the drivers etc. but for the life of me I cannot figure out how to open them up! I have managed to remove the front grill and was able to remove the screws holding the horn-lens and driver but it is still "stuck"
and other than being able to get my arm into the tuning holes, I cannot inspect the speakers
or anything else. i have a pdf drawing of the enclosure and all it's parts but I still cannot figure out how to open it. If I remove the corner protectors will I find screws? Please help!! Also what do those turnable knobs do (L-pad)?
Many thanks and any ideas of why I do not hear high frequency horns would be helpful.

[Don Mascali]

http://www.jblproservice.com/pdf/Cab...ries/4627A.pdf

Remove the woofer and there will be enough room for you to work.
Check all of the connections and then the continuity of the HF driver with a meter.
Knobs are an L pad.

Welcome to the forum and good luck with your project.

[analogean]

Okay, so I eventually was able to remove the speakers from the cabinet.
The woofer is a 140 8 ohm (is supposed to be a 145 in this series).
I tried to measure the Ohmage on the tweeter but got no reading.
I suppose this means that it is blown!! So buying and installing a new diaphragm will solve
this problem, right?
The tweeter is a 16 Ohm 2410 driver with the 2301 "Potato masher" horn. These horns do not seem to be greatly appreciated in this forum and I was wondering why??
Anyway I read that the original diaphragm was Aluminium. There are some originals available "D16R2410" but they cost over $300 each!! The aftermarket 2425 would apparently fit the 2410, is made out of Titanium, and only costs $75.
So what should I get??
Oh, and when I do get new ones how do I replace them?? I don't want to damage something else because of my ignorance!
The question came to mind, why did they blow in the first place?
Before I got them they were being used for music production, mostly synthesizer. Maybe some deeper frequencies were not being filtered out properly??
The crossover circuit is in a sealed riveted box.
How do I open this to check the elements?
When I turn the L-pad I measure from 0 Ohms to about 5 Ohms in the middle and then goes back to zero. Is that the correct behavior for the L-pad??
I have only checked one speaker so far so I don't have a comparison between the two, but the other one is surely blown as well since I was hearing nothing out of the tweeter.
I hope someone can help me out,
many thanks

[Baron030]

The crossover circuit is in a sealed riveted box.
How do I open this to check the elements?
When I turn the L-pad I measure from 0 Ohms to about 5 Ohms in the middle and then goes back to zero. Is that the correct behavior for the L-pad??

Hi

I answered a very similar L-Pad question to yours recently.
The resistance when measured from the high frequency output will go to zero or very nearly zero when the L-Pad is set at its minimum setting because of the shunt resistance between pins 1 and 2. And the resistance will also be zero or very nearly zero when the L-Pad is set at its maximum setting because current can flow through the L1 coil. So, it is normal for the resistance to be higher at it about its mid-point setting. This is because you are measuring the both the L-Pad’s series resistance between pins 2 and 3 combined with the coils dc resistance and the L-Pad’s shunt resistance. So, 5 ohms at a mid-point setting would not be unusual.

Baron030