This is topic Cat 701 hissing noise? in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.
To visit this topic, use this URL:
https://ft-forum.com/ft/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=1;t=003882
Posted by Josh Jones (Member # 447) on 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
Posted by Paul G. Thompson (Member # 655) on 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.
Posted by John Walsh (Member # 168) on 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.
Posted by Paul G. Thompson (Member # 655) on 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? 
Posted by Josh Jones (Member # 447) on 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
Posted by Brad Miller (Member # 2) on 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.
Posted by Paul G. Thompson (Member # 655) on 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.
Posted by Mike Babb (Member # 1379) on 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...
Posted by Paul G. Thompson (Member # 655) on 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.
Posted by Jeff Skallan (Member # 891) on 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
Posted by Gordon McLeod (Member # 33) on 08-21-2002, 10:33 AM:
Dolby switched from Lavezzi to cinemecanica sprockets to make the unit quieter
Posted by Josh Jones (Member # 447) on 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
Posted by Brad Miller (Member # 2) on 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. 
Posted by Paul Konen (Member # 41) on 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.
Posted by Josh Jones (Member # 447) on 08-22-2002, 09:56 AM:
Paul,That was one of the first things I checked, the tension is right.
Josh