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Topic: Swap a JBL driver

Antonio Marcheselli
Phenomenal Film Handler

Posts: 1260
From: Florence, Italy
Registered: Mar 2000

posted 06-03-2002 01:23 PM

Hi everyone.

Seems that one of our theater has blew a HF driver. Which channel? Center of course...

While we have it replaced I'm going to swap it with the one of the left or right channel tonight.

I never disassembled a driver. Is there anything that I should know? Special tools required, some particularly attention...

Any suggestion will be precious!

Bye
Antonio

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Manny Knowles
"What are these things and WHY are they BLUE???"

Posts: 4247
From: Bloomington, IN, USA
Registered: Feb 2002

posted 06-03-2002 05:10 PM

The 2446H driver is heavy. Be careful.

I believe that regular 7/16" bolts mount it to the throat of the horn.

Did I mention that it's a heavy object?

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Steve Guttag
We forgot the crackers Gromit!!!

Posts: 12814
From: Annapolis, MD
Registered: Dec 1999

posted 06-03-2002 06:15 PM

The JBL 244x series drivers (where x can be from 0 to 6)mount with 1/4-20 hardware...four of them in fact. What can blow is the diaphragm (replacement for a 2446H is a D8R2450...accept no imitations or substitutions. Also, one thing to check is the tightness of the "push" terminals...they have been known to come loose and cause intermittent or apparent failure types of response.

Steve

------------------
"Old projectionists never die, they just changeover!"

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Manny Knowles
"What are these things and WHY are they BLUE???"

Posts: 4247
From: Bloomington, IN, USA
Registered: Feb 2002

posted 06-03-2002 08:51 PM

And JBL's diaphragms come with stern warnings regarding its proper installation (by trained JBL techs).

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Randy Stankey
Film God

Posts: 6539
From: Erie, Pennsylvania
Registered: Jun 99

posted 06-03-2002 10:04 PM

So, what is it about those diaphragms that is so special? I have replaced several of them with no problem. I just carefully remove them and put in the new one. I'm careful to make sure that nothing's hitting where it shouldn't be.

Done carefully, it only takes 10-15 minutes to change one. I have even changed one out between shows on a Saturday night.

Is there some secret that eludes me, here?

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Manny Knowles
"What are these things and WHY are they BLUE???"

Posts: 4247
From: Bloomington, IN, USA
Registered: Feb 2002

posted 06-03-2002 11:59 PM

I wondered about that, too..."the device is not self-centering" or something like that...goes on to say something about requiring special gear and training.

Beats me.

Maybe somebody can explain if this is for real or just a corporate disclaimer.

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Paul G. Thompson
The Weenie Man

Posts: 4718
From: Mount Vernon WA USA
Registered: Nov 2000

posted 06-04-2002 12:06 AM

If you are going to change the diaphragm, DO NOT USE A FERROUS METAL SCREWDRIVER!! When you have the magnet suck your screwdriver from your hand and punch a hole into your new diaphragm, then you will know why.

Use a copper, brass, or aluminum screwdriver, or any appropiate screwdiver that is not attracted by magnets.

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Antonio Marcheselli
Phenomenal Film Handler

Posts: 1260
From: Florence, Italy
Registered: Mar 2000

posted 06-04-2002 02:45 AM

Thanks to all for the suggestions.
However I didn't swap the driver. Seems that was the CP500 was kidding. My colleague reset it many times and the problem disappeared.

It is VERY strange because that problem (a cawing from the center channel) was there since yesterday and from the THX monitor cannot be heard (he tried with a pair of Grado headphones too!).

But then the problem disappeared... I really know that CP500 can cause so strange problems, but why on two differents day... ??

We will follow this. Thanks for your help.

Paul,

You're right, I put few times a screwdriver near a driver...

Bye

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Steve Guttag
We forgot the crackers Gromit!!!

Posts: 12814
From: Annapolis, MD
Registered: Dec 1999

posted 06-04-2002 07:50 AM

The 2446 DOES use a self centering diaphragm (it is pinned for registration). I guess, you can install it rotated by 180 degrees so the extra space for the in/out leads don't line up. Also, you should make sure the air-gap is cleaned out really well. One thing a genuine JBL certified technician will have is an appropriate gap gauge to verify that the magnet structure hasn't shifted. The 2446 should be able to pass a .036" gap gauge all of the way around.

Steve

------------------
"Old projectionists never die, they just changeover!"

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David Koegel
Film Handler

Posts: 55
From: Alexandria, VA
Registered: Jun 99

posted 06-04-2002 10:10 AM

And when replacing the diaphram, make sure that you are working in a fairly clean area. Most important is to clean around the edges of that diaphram before you remove it. That gap in the magnet can easily suck in some tiny pieces of magnetic material (read: metal filings), and once in they are in there, I imagine they are very difficult to remove.

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Manny Knowles
"What are these things and WHY are they BLUE???"

Posts: 4247
From: Bloomington, IN, USA
Registered: Feb 2002

posted 06-04-2002 10:24 AM

Sounds to me like this is one of those "simple procedures" where there is only one way to do it correctly and over a dozen ways to screw it up.

Usually, I need to SEE somebody do it correctly at least once before I feel comfortable doing it myself.

Pictorial guide, anyone?

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Antonio Marcheselli
Phenomenal Film Handler

Posts: 1260
From: Florence, Italy
Registered: Mar 2000

posted 06-04-2002 05:26 PM

Uhm...

Luckily I had no need to touch that driver!!

Bye
Antonio

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Michael Gonzalez
Jedi Master Film Handler

Posts: 790
From: Grand Island , NE USA
Registered: Sep 2000

posted 06-05-2002 01:12 AM

The hard part isn't replacing the Diaphram it's climbing behind the screen and putting the Driver back by yourself. Try holding a 25lb driver in the air with one hand while trying to screw it back on to the base with ther other hand. Not Fun. Oh and you have to be really careful not to drop the horn and tear a hole into the screen because our screens were not really design for anyone to climb behind them. There are wires everywhere and not very much room to work back there. I got lucky and was able to get it done and it isn't an expirance that I would like to relive any time soon.

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Manny Knowles
"What are these things and WHY are they BLUE???"

Posts: 4247
From: Bloomington, IN, USA
Registered: Feb 2002

posted 06-05-2002 06:59 AM

I had to b*tch and moan to get an extra 12" of space and an AC outlet behind the screen. Good thing, too because I later upgraded one of those screens to speakers with much larger horns.

It's always good to have help replacing or installing one of those heavy drivers. I usually try to get two helpers if I can.

------------------
~Manny.

"The brown acid that is circulating around is not specifically too good."

-- An announcement in the film, "Woodstock: 3 Days of Peace & Music."

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John Walsh
Film God

Posts: 2490
From: Connecticut, USA, Earth, Milky Way
Registered: Oct 1999

posted 06-05-2002 05:26 PM

It would also be a lot nicer if the driver had 4 studs sticking out to hold it in place, (while you screw nuts on) rather than the way it is actually designed (you have to hold the damn thing up while trying to get the bolts to thread through.)

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