Film-Tech Forum ARCHIVE: Are LEDs all the same?

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Posted by Randy Stankey (Member # 64) on 02-07-2011, 05:57 PM:

The LED in analog sound head of my projector is working all right but it are coming to the end of their life. It is 15 years old. I have the power supply almost topped out to get Dolby level in the CP-650. I don't have to do it yet but the time will come to change it soon.

I have some LEDs from a Dolby Digital reader that I found in the bottom of my tool box, left over from working at Cinemark.

Are these the same LEDs that can be used for the analog soundtrack? I have the Component Engineering reader.

I also have a BACP DSTR-20 Dolby Digital reader. Again, is this the same LED?

It'd be nice to know that I can use these to replace the old LEDs when the time comes.

Posted by Jeremy Weigel (Member # 4208) on 02-07-2011, 06:19 PM:

Hey Randy,

I take it from this thread that they most likely are the exact same LED.

Posted by Gordon McLeod (Member # 33) on 02-07-2011, 07:08 PM:

The only note of caution there were some leds that didn't meet dolby's specs that did get in the market place

Posted by Randy Stankey (Member # 64) on 02-07-2011, 11:59 PM:

Are those the ones where some of the segments inside were burning out?

I specifically remember that we had to go around and replace a bunch of LEDs with bad segments. The ones I have would have been out of the batch used to replace the bad ones.

Posted by Scott Norwood (Member # 30) on 02-08-2011, 09:59 AM:

Personally, I would order the complete LED assembly. Replacing just the LED part looks rather un-fun, whereas the entire assembly (which would be specific to the reader that you are using) would be a fairly quick swap. Obviously, some of this decision depends upon the balance of available time and available funds.

Posted by Sam D. Chavez (Member # 1841) on 02-08-2011, 10:36 AM:

Randy,

How far back are you going? Were the LEDs Red or IR?

Posted by Randy Stankey (Member # 64) on 02-08-2011, 01:26 PM:

They are red.

They were supposed to replace bad LEDs in Dolby Digital Cat. 701 readers. We had a string of them where some of the elements inside the LED were dying prematurely. We bought them by the dozen.

After I left the job and turned in all my equipment, I kept finding odd things in my tool boxes and in the trunk of my car. I'd find odd nuts, bolts and sprockets and all sorts of odd things. Some of the stuff I sent back. It was probably a year after I changed jobs that I found the LEDs tucked down in one of the pockets in the lid of my tool box, still in their little plastic tray. It'd been such a long time since I was gone, I just tucked them back in there and forgot about them.

Now that I'm working on projector sound systems again, I was reminded that I still have two or three of those babies floating around here, somewhere.

I figured I'd put them to good use.

I got pretty used to installing the bare LEDs versus the modules.
I don't have a problem with soldering them in, if necessary.

Did you say that some of them were glued in place? Or, was it just the heat sink compound that glued them down? Had that happen before.

Posted by Sam D. Chavez (Member # 1841) on 02-08-2011, 03:08 PM:

AFAIK, BACP is the only one intentionally gluing in LEDs and this is only on the Kinoton where there is no room for a retainer.

Posted by Louis Bornwasser (Member # 3063) on 02-08-2011, 04:09 PM:

I've seen very old Component leds that were glued in or is my recall bad? Louis

Posted by Steve Guttag (Member # 268) on 02-08-2011, 04:46 PM:

Your recall is bad.

CE LEDs were always socketed...right back to the IR days. There was a brief period on the switch to the visible RED LEDs where the wires that came from the LED socket were RTVed to the "SPUD" plate...they then made that flex cable thing which is screwed to the SPUD plate.

-Steve