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» Film-Tech Forum ARCHIVE   » Operations   » Film Handlers' Forum   » 5-Star Reverse Scan problem: (Page 1)

 
This topic comprises 3 pages: 1  2  3   
Author Topic: 5-Star Reverse Scan problem:
Wolff King Morrow
Master Film Handler

Posts: 490
From: Denton, TX, USA
Registered: Feb 2004

- posted 10-16-2004 02:38 AM      Profile for Wolff King Morrow   Author's Homepage   Email Wolff King Morrow   Send New Private Message       Edit/Delete Post 
I've been trying to tackle a bad "buzzing" sound coming from one of our auditoriums during analog sound playback. I was able to rule out the sound processor as the cause and eventually traced the buzzing sound to the analog reverse scan reader in the 5-Star. So I tried replacing the pre-amp board mounted behind the solar-cell, but it had no effect on the buzzing problem. I also noted that touching the shielded wire that connects the solar cell to the pre-amp causes the buzzing noise to intensify greatly.

I did a word search here on the forums, but couldn't find an exact match for my problem. Is the solar cell to blame for the problem? If so, how difficult is it to install a new one? I know the LED requires careful alignment, but what about the solar cell? Basically I just need to know if this requires a tech visit. Thanks for your help!

PS: The problem is starting to slightly creep up in a couple of other auditoriums, so I'm assuming this is maybe a common part wearing out.

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Brad Miller
Administrator

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

- posted 10-16-2004 02:42 AM      Profile for Brad Miller   Author's Homepage   Email Brad Miller       Edit/Delete Post 
You weren't specific as to whether you only hear the buzz during the running of a film or not. Tomorrow stick a business card in between the film and red light source before you thread up the first show. Now switch to SR and listen for hum. Is it there? If so, then it is something in the preamp or wiring. If it is not there, try turning the xenon and projector motor on with the business card still in place. Did either initiate a hum? If still no hum, your optical A-chain alignment is at fault.

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Richard Hamilton
Phenomenal Film Handler

Posts: 1341
From: Evansville, Indiana
Registered: Jan 2000

- posted 10-16-2004 06:43 AM      Profile for Richard Hamilton   Email Richard Hamilton   Send New Private Message       Edit/Delete Post 
quote: Brad Miller
Tomorrow stick a business card in between the film and red light source before you thread up the first show.
Brad, where does he stick the card if he hasn't threaded up yet? [Razz]

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Steve Guttag
We forgot the crackers Gromit!!!

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

- posted 10-16-2004 07:56 AM      Profile for Steve Guttag   Email Steve Guttag   Send New Private Message       Edit/Delete Post 
The key is to find out if the noise is generated by the film (poor lateral alignment). So before loading the film, Brad is having him block the LED to see if the noise is there because if it is, it isn't poor film alignment.

If the noise is there only with the film running and blocking the LED with the business card kills the noise...it indicates a poor alignment.

Is the buzz channel specific?

I would recommend using Dolby-A or Mono at first when trying to check the problem since mono has no noise reduction and A has much less than SR but will let you see a channel specific noise.

Steve

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Edward Jurich
Master Film Handler

Posts: 305
From: Las Vegas USA
Registered: Jul 2003

- posted 10-16-2004 09:06 AM      Profile for Edward Jurich   Email Edward Jurich   Send New Private Message       Edit/Delete Post 
I had a buzz problem here in the analog (analog is all we run) sound. The buzz was much worse when the processor was switched to mono, this is because the Dolby noise reduction will mask the buzz but then the buzz modulates with audio. Anyway, the problem turned out to be the house light dimmers (SCR or TRIAC solid state). The solution was to disconnect the shield wire at both ends from the cell to the processor. You can get away with no shield connected if your processor has a balanced input. And no, bypassing the SCR/TRIAC's or changing ground circuits did not help.

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Mark Gulbrandsen
Resident Trollmaster

Posts: 16657
From: Music City
Registered: Jun 99

- posted 10-16-2004 09:44 AM      Profile for Mark Gulbrandsen   Email Mark Gulbrandsen   Send New Private Message       Edit/Delete Post 
quote: Wolf King Morrow
The problem is starting to slightly creep up in a couple of other auditoriums, so I'm assuming this is maybe a common part wearing out.
The clue is the above quote.....I'd be willing to bet that the spring loaded flange side of your lateral guide roller is stuck open. This is a very common problem with all Simplex sound head lateral guide rollers. The lateral guide must be removed from the reproducer and dissassembled and cleaned, bad parts replaced(check the shaft carefully, they do wear!), re-lubed, and re-installed. Then do an "A" chain on the thing.

Hint: Lube it with LaVezzi or some other light weight Mobil-1 type synthetic oil and the flange sticking won't happen again. These lateral guide assys. should really be taken apart and cleaned once a year during normal maintainance. If you find it is this then your not getting all the normal maintainance that you should be getting.

Mark @ CLACO

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Steve Guttag
We forgot the crackers Gromit!!!

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

- posted 10-16-2004 10:34 AM      Profile for Steve Guttag   Email Steve Guttag   Send New Private Message       Edit/Delete Post 
quote: Edward Jurich
The solution was to disconnect the shield wire at both ends from the cell to the processor. You can get away with no shield connected if your processor has a balanced input.
Correctly stated, you found a band-aid for your problem. Not a solution.

Whom ever told you that just because you have balanced inputs negates the need for a proper shield doesn't have a clue as to what they are talking about. What you just gave was very bad advice/information.

Steve

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Wolff King Morrow
Master Film Handler

Posts: 490
From: Denton, TX, USA
Registered: Feb 2004

- posted 10-16-2004 04:02 PM      Profile for Wolff King Morrow   Author's Homepage   Email Wolff King Morrow   Send New Private Message       Edit/Delete Post 
Thanks for the suggestions. The Buzz problem is constantly there, whether film is running or not. Thankfully we only kick over to analog during ads, but most of the trailers and the movie are played via DTS. I will check it with a card like Brad said tonight just to confirm.

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Brad Miller
Administrator

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

- posted 10-16-2004 05:26 PM      Profile for Brad Miller   Author's Homepage   Email Brad Miller       Edit/Delete Post 
Do you get the buzz in non-sync if you stop your cd player?

Do you get the buzz in mono/A/SR if you turn the fader down to 0?

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Michael Schaffer
"Where is the
Boardwalk Hotel?"

Posts: 4143
From: Boston, MA
Registered: Apr 2002

- posted 10-16-2004 05:31 PM      Profile for Michael Schaffer   Author's Homepage   Email Michael Schaffer   Send New Private Message       Edit/Delete Post 
quote: Wolff King Morrow
So I tried replacing the pre-amp board mounted behind the solar-cell, but it had no effect on the buzzing problem.
That sounds like you have BACP readers. In addition to the shield, this reader also has a ground terminal which you can connect to the sound rack ground. This has helped me to get rid of humming in a few cases.

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Richard Hamilton
Phenomenal Film Handler

Posts: 1341
From: Evansville, Indiana
Registered: Jan 2000

- posted 10-16-2004 11:21 PM      Profile for Richard Hamilton   Email Richard Hamilton   Send New Private Message       Edit/Delete Post 
quote: Steve Guttag
The key is to find out if the noise is generated by the film (poor lateral alignment). So before loading the film, Brad is having him block the LED to see if the noise is there because if it is, it isn't poor film alignment.
I know, I was just being a smart ass [Big Grin] Brad said to stick the card between the film and the light source before he threaded up! If he hasn't threaded yet, the film is still on the platter or reels. [Wink]

Rick

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Wolff King Morrow
Master Film Handler

Posts: 490
From: Denton, TX, USA
Registered: Feb 2004

- posted 10-17-2004 01:34 AM      Profile for Wolff King Morrow   Author's Homepage   Email Wolff King Morrow   Send New Private Message       Edit/Delete Post 
Hey guys!

I got to the bottom of the problem, which turns out has been mentioned here before. It ended up being the House & Stage light switch box on the wall causing the buzzing sound. The moment I turned the lights off while troubleshooting, the buzzing stopped. So I turned the lights back on and the buzz came back.

I guess this means a tech visit is in order because this sort of problem requires some serious re-wiring I bet.

BTW I checked all our lateral guide rollers and they are all in working order.

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Brad Miller
Administrator

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

- posted 10-17-2004 02:24 AM      Profile for Brad Miller   Author's Homepage   Email Brad Miller       Edit/Delete Post 
Out of curiosity, what kind of dimmers do you have?

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Wolff King Morrow
Master Film Handler

Posts: 490
From: Denton, TX, USA
Registered: Feb 2004

- posted 10-17-2004 04:16 AM      Profile for Wolff King Morrow   Author's Homepage   Email Wolff King Morrow   Send New Private Message       Edit/Delete Post 
Something like: "Dual Auditorium Light Dimmers" according to the manuals. I'll have to check the exact name and make when I go back to work on Tuesday.

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Gordon McLeod
Film God

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

- posted 10-17-2004 01:04 PM      Profile for Gordon McLeod   Email Gordon McLeod   Send New Private Message       Edit/Delete Post 
In a perfect world lamp dimmers should not be wired onto the same pahse as lowlevel components of the soundsystem (ideally soundsystems should have a deditcate technical power transformer and isolated grounding system)
In this case one should check that the dimmer isn't on the same phase and if it is a problem that has sudenly surfaced check neutral connections and ground connections also check that the filter choke in the dimmer hasn't failed and shorted out

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