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Topic: Cat 701 hissing noise?

Josh Jones
Redhat

Posts: 1207
From: Plano, TX
Registered: Apr 2000

posted 08-19-2002 11:48 AM

My cat. 701 is making a hissing noise somewhere in the film path area. Is this normal? The head is new, and so far has two hours of run time on it.

Josh

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Paul G. Thompson
The Weenie Man

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

posted 08-19-2002 02:51 PM

Josh, get a hunk of plastic tubing about 1/2 inch or 3/8 inch inner diameter from your hardware store and use it as a stethoscope to locate the noise.

If it is just sitting there and hissing, check and see what your cat is.

You didn't say if you were running film through it or not when it is hissing, but I presume you are. It could be something mechanical such as the bearings in the little pad rollers or the flywheel dragging on something. More than likely, it is from the pad rollers or the guide rollers themselves.

It could also be noise being emitted from the LED power supply for one reason or another.

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John Walsh
Film God

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

posted 08-19-2002 09:05 PM

I notice on the 701's (and the 700's too) the sprocket "sings" where the film goes on the bottom. Or, perhaps the wire from the power supply (to the LED) is rubbing lightly against the flywheel. I've heard some switching power supplies make a hissing-like noise. Yoiu could remove the rear cover/power supply and listen just to it.

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Paul G. Thompson
The Weenie Man

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

posted 08-19-2002 09:58 PM

John:

Indeed, some sprockets do sing...and it is loud and clear when they do!!!!

Come on, Dolby Engineers.....the singing sprocket issue has been around since the CAT 700 was introduced. Don't you think it is about time to look into it for a possible fix?

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Josh Jones
Redhat

Posts: 1207
From: Plano, TX
Registered: Apr 2000

posted 08-19-2002 11:44 PM

it does it when film is running only. its in the loop somewhere, but I cant really locate it.

Josh

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Brad Miller
Administrator

Posts: 17775
From: Plano, TX (36.2 miles NW of Rockwall)
Registered: May 99

posted 08-20-2002 12:19 AM

I've never known an SRD penthouse to make any noise. Make sure the pad rollers have proper clearance from the sprocket and also check to see that the guide rollers are properly lined up with the sprocket laterally. Those would be my first guesses.

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Paul G. Thompson
The Weenie Man

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

posted 08-20-2002 02:26 AM

Brad, that was some of the things I tried on two CAT 700's we had/have since I installed a DA-10 and a CP-500. I finally gave up and said "to hell with it", and accepted it as a normal thing. And, I agree, many I have heard is as quiet as a mouse.

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Mike Babb
Master Film Handler

Posts: 250
From: Norwich UK
Registered: Jul 2002

posted 08-20-2002 02:33 AM

My 699 and 700 tend to buzz more when people put more tension on it, but seems like some films also tend to buzz more. If I remember right a guy from Dolby or at least our old tech said this was "normal". I usually don't hear it when I thread but one extra sprocket of tension will make it happen. Maybe this is what you're hearing though...

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Paul G. Thompson
The Weenie Man

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

posted 08-20-2002 02:41 AM

Mike, the tension will make a difference. Mine buzzed no matter what tension I used. And, yes...some films buzzed more than others. So did some reels of the same print.

As I think of it, I wonder if there might have been a run of bad sprockets. That could happen.....The longer the print is run, the quieter mine became, but I never saw sprocket holes laying on the floor.

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Jeff Skallan
Film Handler

Posts: 65
From: Littleton, CO, USA
Registered: May 2001

posted 08-20-2002 04:05 AM

Josh,

I've heard a few CAT 700s buzz and hiss. In my experience this is usually caused by a loose or misaligned pad roller in the penthouse. Also on occasion I've found that using the tension spring inside the Christie platter brain will slightly increase the hissing noise, but doesn't really adversely affect the film. (I actually like to leave it in place rather than removing it while threading though the CAT 700.)

I've experimented with removing the brain holdback spring to find the hissing noise quiet down, but the error rating from our DA-20 went up by 3 points! Interesting enough, while manually holding the film edges with my fingers between the platter and projector with an increased amount of tension in this same instance, I've been able to produce error ratings of "0" on the DA-20. Unless the hiss noise is unusually intense, I have to agree with Mike and Paul that it may be quite normal to hear a bit of it from various film stocks.

My 2 cents worth...
-- Jeff

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Gordon McLeod
Film God

Posts: 9532
From: Toronto Ontario Canada
Registered: Jun 99

posted 08-21-2002 10:33 AM

Dolby switched from Lavezzi to cinemecanica sprockets to make the unit quieter

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Josh Jones
Redhat

Posts: 1207
From: Plano, TX
Registered: Apr 2000

posted 08-22-2002 03:43 AM

I believe the "shooshing" noise is coming form one of the spring-loaded guidance rollers at the front of the head. It is fairly obnoxious, and can be heard above the noise of the machine.

Josh

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Brad Miller
Administrator

Posts: 17775
From: Plano, TX (36.2 miles NW of Rockwall)
Registered: May 99

posted 08-22-2002 04:01 AM

Run some film and physically stop the rollers from spinning one at a time. If that doesn't isolate it, try loading up some junk film and find new creative ways to thread the machine, skipping a different roller each time. It won't take long to find out if you indeed have a noisy roller.

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Paul Konen
Jedi Master Film Handler

Posts: 981
From: Frisco, TX. (North of Dallas)
Registered: Jun 99

posted 08-22-2002 09:03 AM

I find that if you have too much tension with the pad rollers, then you will get extra noise. The pad roller arms should be even with the white half moon that is behind each roller arm.

Paul.

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Josh Jones
Redhat

Posts: 1207
From: Plano, TX
Registered: Apr 2000

posted 08-22-2002 09:56 AM

Paul,

That was one of the first things I checked, the tension is right.

Josh

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