Film-Tech Cinema Systems
Film-Tech Forum ARCHIVE


  
my profile | my password | search | faq & rules | forum home
  next oldest topic   next newest topic
» Film-Tech Forum ARCHIVE   » Operations   » Film Handlers' Forum   » Digital LED vs Analog LED failure. Effects on analog? (Page 1)

 
This topic comprises 2 pages: 1  2 
 
Author Topic: Digital LED vs Analog LED failure. Effects on analog?
Eric Robinson
Jedi Master Film Handler

Posts: 538
From: Santa Rosa, CA
Registered: Jan 2005


 - posted 07-23-2006 08:20 PM      Profile for Eric Robinson   Email Eric Robinson   Send New Private Message       Edit/Delete Post 
Posting this topic will either illuminate me as an intellectual or total idiot. I am willing to sacrifice myself; however, due to curiosity.

When one or more LED elements of a visible red LED, typically used in a Simplex basement reader, fail or start failing it can be observed using a scope hooked up to the video and trigger outputs of a dolby processor. I fully understand the effect of the elements which are not perfoming well in a digital reader application. What I'm wondering about, though, is supposing one or more elements fail or have comprimising performance in a visible red LED used for an analog reader. Other than a noticeable lower light output level, are there any other artifacts introduced in this scenerio. Distortion, loss ???

 |  IP: Logged

Mark Gulbrandsen
Resident Trollmaster

Posts: 16657
From: Music City
Registered: Jun 99


 - posted 07-23-2006 09:02 PM      Profile for Mark Gulbrandsen   Email Mark Gulbrandsen   Send New Private Message       Edit/Delete Post 
quote: Eric Robinson
Other than a noticeable lower light output level, are there any other artifacts introduced in this scenerio. Distortion, loss ???

You're correct but there is a little more to it. Add in drastically increased distortion and alot of phase shift. Most decoders cannot deal with this sort of incomming signal problem and they tend to end up doing some very strange things. you might be able to squeek by with a simlge segment failed till you can get back to replace the LED... perhasp a day or so but usually by then the intensity has also petered out for the most part. Any more than one element out and immediate replacement should be done. This is but one very good reason for installing BACP readers... Although I have yet to change even one of their LED's it can actually be changed while the film is running if need be! Levels can then be set when the show is over and the LED has at least had some time to settle in.

Mark

 |  IP: Logged

Eric Robinson
Jedi Master Film Handler

Posts: 538
From: Santa Rosa, CA
Registered: Jan 2005


 - posted 07-26-2006 10:06 AM      Profile for Eric Robinson   Email Eric Robinson   Send New Private Message       Edit/Delete Post 
That's interesting to hear that there are artifacts such as distortion and phase shift. Correct me if I'm wrong, but doesn't Dolby logic decoding base its decoding scheme on the phase relationship of the left and right audio channel. If so, it would seem that phase distortion would cause the decoding scheme to produce unusual results. Is this true?

Also, it is somewhat easy to diagnose a failing digital LED by viewing the video signal on a scope. In the case of the analog LED; however, I'm unaware of any way to view its output performance other than the naked eye. Any suggestions?

 |  IP: Logged

Mark Gulbrandsen
Resident Trollmaster

Posts: 16657
From: Music City
Registered: Jun 99


 - posted 07-26-2006 01:00 PM      Profile for Mark Gulbrandsen   Email Mark Gulbrandsen   Send New Private Message       Edit/Delete Post 
Best thing to do is check the current draw on the led. This is the best way to determine the end of the LED's life. Looking at it with the naked eye is not a good thing. I use a layer of darak film over the led.

Mark

 |  IP: Logged

John Hawkinson
Film God

Posts: 2273
From: Cambridge, MA, USA
Registered: Feb 2002


 - posted 07-26-2006 01:14 PM      Profile for John Hawkinson   Email John Hawkinson   Send New Private Message       Edit/Delete Post 
Well, for an analog LED, I think the big issue is relative gain between the left and right channels. So as long as you run 69T and set your preamp gains appropriately, you are probably just fine.

If one channel is radically different from the other (e.g. several pot turns), then there's a good chance something is wrong (or needs cleaning).

--jhawk

 |  IP: Logged

Steve Guttag
We forgot the crackers Gromit!!!

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


 - posted 07-26-2006 01:35 PM      Profile for Steve Guttag   Email Steve Guttag   Send New Private Message       Edit/Delete Post 
John, you are wrong...the LED in a typical reverse scan system is not as uniform as one would hope. If elements are out, then the uniformity of the light will be off. Merely raising the level based on Dolby Tone will not correct the problem since the light will remain inconsistant where the elements are bad.

Picture, if you will, a dark spot on your glasses...you eye may open its iris a bit more to let more light in...but you still have that dark spot as you look out. Now if you merely put a very weak sunglass over one lens such that your iris could balance things out, then that would be another story. In fact, it wouldn't surprise me at all to find that human eyes do not perceive light intensity identically within the same individual.

 |  IP: Logged

Gordon McLeod
Film God

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


 - posted 07-26-2006 01:36 PM      Profile for Gordon McLeod   Email Gordon McLeod   Send New Private Message       Edit/Delete Post 
As the segments fail the eveness of track illumination gets worse causing level and pahse errors and distortion

 |  IP: Logged

Kenneth Wuepper
Phenomenal Film Handler

Posts: 1026
From: Saginaw, MI, USA
Registered: Feb 2002


 - posted 07-26-2006 02:27 PM      Profile for Kenneth Wuepper   Email Kenneth Wuepper   Send New Private Message       Edit/Delete Post 
Does anyone use the uniform illumination test film "snake Track"?

That used to be a valuable tool for detecting sagging exciter lamp filaments and also crystallized filament wires.

I would think that this test would be equally useful in determining dead or dim elements in the LED array.

KEN

 |  IP: Logged

Sam D. Chavez
Film God

Posts: 2153
From: Martinez, CA USA
Registered: Aug 2003


 - posted 07-27-2006 09:04 AM      Profile for Sam D. Chavez   Author's Homepage     Send New Private Message       Edit/Delete Post 
The snake track has been rendered obsolete by the Dolby 566 illumination uniformity track. It uses 6 tracks alongside each other on octave centers to produce a bar graph display on an RTA. Way better and you can see changes an adjustment in real time.

[ 07-28-2006, 01:15 AM: Message edited by: Sam D. Chavez ]

 |  IP: Logged

Kenneth Wuepper
Phenomenal Film Handler

Posts: 1026
From: Saginaw, MI, USA
Registered: Feb 2002


 - posted 07-27-2006 03:17 PM      Profile for Kenneth Wuepper   Email Kenneth Wuepper   Send New Private Message       Edit/Delete Post 
Thanks, Sam.

I knew that there must be a current better "CAT" way of catching the mouse.

KEN

 |  IP: Logged

Frank Dubrois
Jedi Master Film Handler

Posts: 896
From: Cleveland, OH
Registered: Mar 2005


 - posted 07-28-2006 01:00 AM      Profile for Frank Dubrois     Send New Private Message       Edit/Delete Post 
that 566 test film seems to be some handy stuff. About time I get some.

Mark,

Do you know offhand if NT sells that film? I'm a fan of their stuff since you last brought them up. Thanks [thumbsup]

 |  IP: Logged

Sam D. Chavez
Film God

Posts: 2153
From: Martinez, CA USA
Registered: Aug 2003


 - posted 07-28-2006 01:13 AM      Profile for Sam D. Chavez   Author's Homepage     Send New Private Message       Edit/Delete Post 
Dolby is the only manufacturer of 566. It's very cool stuff in the last days of analog.

 |  IP: Logged

Louis Bornwasser
Film God

Posts: 4441
From: prospect ky usa
Registered: Mar 2005


 - posted 07-28-2006 08:33 AM      Profile for Louis Bornwasser   Author's Homepage   Email Louis Bornwasser   Send New Private Message       Edit/Delete Post 
Because of the way 566 is made it is fairly unlikely anyone else will make it soon. It is the outgrowth of the amazing, 6 channel discrete Dolby format proposed in the early 80's. Dual inventory requirements killed it. Louis

 |  IP: Logged

Mark Gulbrandsen
Resident Trollmaster

Posts: 16657
From: Music City
Registered: Jun 99


 - posted 07-28-2006 09:10 AM      Profile for Mark Gulbrandsen   Email Mark Gulbrandsen   Send New Private Message       Edit/Delete Post 
Frank,
CLACO can supply you with any test film you need in any length or quantity. Call Vince at our office after 9am Mountain time to order. We tke VISA/MC.

Mark

Office 801-355-1250
Fax 801-355-1259

 |  IP: Logged

Eric Robinson
Jedi Master Film Handler

Posts: 538
From: Santa Rosa, CA
Registered: Jan 2005


 - posted 08-01-2006 03:55 AM      Profile for Eric Robinson   Email Eric Robinson   Send New Private Message       Edit/Delete Post 
Now to follow up on Marks comment about BACP readers!

I have only replaced Dolby LEDs so far, can you, (Mark), explain the method of LED replacement for the BACP readers? and why it is so easy compared to replacing an LED of any other brand?

Thanks...ERIC

 |  IP: Logged



All times are Central (GMT -6:00)
This topic comprises 2 pages: 1  2 
 
   Close Topic    Move Topic    Delete Topic    next oldest topic   next newest topic
 - Printer-friendly view of this topic
Hop To:



Powered by Infopop Corporation
UBB.classicTM 6.3.1.2

The Film-Tech Forums are designed for various members related to the cinema industry to express their opinions, viewpoints and testimonials on various products, services and events based upon speculation, personal knowledge and factual information through use, therefore all views represented here allow no liability upon the publishers of this web site and the owners of said views assume no liability for any ill will resulting from these postings. The posts made here are for educational as well as entertainment purposes and as such anyone viewing this portion of the website must accept these views as statements of the author of that opinion and agrees to release the authors from any and all liability.

© 1999-2020 Film-Tech Cinema Systems, LLC. All rights reserved.