Film-Tech Forum ARCHIVE: Dolby Digital problems:

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Posted by Wolff King Morrow (Member # 2226) on 10-10-2005, 06:21 PM:

I need to ask for opinions on what's going on with one of my DD setups. Some months ago I noticed the LED was a little too dim and causing problems, so I had a tech adjust the voltage (which I now know how to do myself). That solved the problem fine and good. I've since made note that the error rate is generally higher than it should be on that projector, where it is on average 6 to 6.5 even with a film cleaner. My other DD projector can hold an error rate of 2.5 without the use of a film cleaner, so I'm suspecting the LED needs to be replaced. The voltage dial in the reader appears to be maxed out as it is.

Now though, I've been alerted to a problem with a print of "Two for the Money", which was reverting to analog at usually the 4th reel, though the entire print's error rate was at 7.5 to failing. The problem is the analog has a 50-50 chance of being completely frozen in silence when the DA20 kicks over to it. The only way out of it was to stop the projector, reset the sound rack breakers and reboot the entire sound rack in the hopes of getting the sound to kick back in from being dead. Needless to say, this was unacceptable, so I moved the offending print to a different location.

Now I've read over the DA20 manual and it vaguely mentions the problem of the analog being frozen as something you might have to deal with by cutting off the power to the DA20 and then manually selecting the analog sound on your processor. The only problem is this did not work when I tried it. The sound was still completely silent in analog mode.

At any rate, the tech that services my area is in Europe right now, and the other tech was unable to help me over the phone. I figured I might see if anyone here knows of this problem and knows of a way to successfully bypass analog without it being frozen. Thanks a bunch for your help!

My setup:

Strong Highlight II console
CNA 150 automation
Dolby Digital reader
Reverse Scan LED analog 5 Star Sound

Ultra Stereo DSP -60s processor
DA20 DD processor
Dolby SA-10

BGW amp garbage...

Posted by Monte L Fullmer (Member # 2797) on 10-11-2005, 12:46 AM:

Ummmm..basement reader for a 5-star head... GROOVY! Might have some bad, or iffy bearings in the scanner drum, lateral guide roller bearings. I've got the basic same problem with my basement 5-star SR-D reader. (time to think about CAT-702/BACP penthouse readers...but have to convince the owner on this one..lol)

Easy way is to shut off the DA-20 (open up the back and unplug the power cord for the DA-20), or turn off the power that runs the LED to the SRD camera - either way to "force" the processor to run optical and stay there for the time being.

I hooked up my laptop to my DA-20 and ran the WinDRAS program and I've got jumping around of the "square" like nobody's business on the display due to "5" to "F" error readings.

Rip apart that 5-star and pull out the flywheel shaft and check your bearings...

BGW amps are fine, nothing wrong with them... [Smile]

-Monte

Posted by Wolff King Morrow (Member # 2226) on 10-11-2005, 05:44 AM:

I kind of doubt there's anything wrong with the sound head, its seems more how the DD processor handles kicking over to analog sound. Sometimes the sound is frozen, most of the time it plays. I'm pretty sure there's some sort of processor problem on this one. Just in case, I'll check the bearings as you suggest. It just seems like more of a computer error issue, or at least that's my gut reaction to how it was behaving. Of course, if it were the sound head, that would make it easier to fix and prevent next time. Perhaps I should turn off the DD reader and test it out.

Hee hee! I'm sorry, but the BGW amps blow. Just ask Heath Dutton about this and he'll know exactly where I'm coming from. [Wink]

Posted by Michael Schaffer (Member # 1204) on 10-11-2005, 06:37 AM:

When it reverted, was your analog processor on projector 1 or 2 input?

Posted by Brad Miller (Member # 2) on 10-11-2005, 12:08 PM:

First don't forget that you can have the led too bright! Just turning up the knob isn't the proper way to fix it, but in a pinch you can do it as long as you adjust up and down seeking for the lowest possible error number and realize that may still not be the proper setting, but one that appears to be the best setting for that reel of film.

I've never used those USL processors, so you may want to ask Clint at USL about that issue with the analog. However have you tried physically flipping the two DA20s and see if the problem follows the DA20? None of your settings will be off by doing this assuming both projectors and processors are the same. However remember that you cannot "hot swap" them, so make SURE you have the entire breaker panel powered down before you unplug anything.

Odds are though that your problem is that the soundhead isn't aligned properly.

Posted by Wolff King Morrow (Member # 2226) on 10-11-2005, 04:56 PM:

The thing about the sound head is we literally JUST had a PM visit, where the techs checked the alignment of all the sound heads on each projector.

I'm not sure I can swap the DA20's as the other one is hooked up with a 6AD DTS processor. Unless of course that doesn't matter and they are both configured the same way.

The LED voltage was adjusted by the tech, so I assumed he knew what he was doing. However, when I checked it, the dial was maxed out.

Posted by Louis Bornwasser (Member # 3063) on 10-12-2005, 09:38 AM:

Did this work OK before the tech adjusted it? Louis

Posted by Richard Hamilton (Member # 321) on 10-12-2005, 03:08 PM:

Ha,Louis, I was just reading this post and was going to ask the same question.

Rick

Posted by Wolff King Morrow (Member # 2226) on 10-12-2005, 04:25 PM:

If you mean analog sound, I suppose so. Thing is I never had the sound go completely silent when it kicks over to analog before, so this is a completely new problem for me. The LED voltage on the DD reader had been adjusted several months ago though.

Posted by Michael Schaffer (Member # 1204) on 10-12-2005, 07:38 PM:

It can go silent when it reverts to analog and projector 2 input is activated by accident. That happened in one of my locations a little while ago.

Posted by Robert John Jeromson (Member # 2559) on 10-13-2005, 03:10 PM:

The DA-20's in the last location I worked in would also, occasionally, go silent when reverting to analogue, especially on startup, if the automation was set for digital but the first ad was SR.

Posted by Wolff King Morrow (Member # 2226) on 10-23-2005, 04:48 PM:

I finally caught the problem last night and it was something I have repaired on other projectors before, but I just had forgotten about this particular issue. It was the Kelmar pre-amp box randomly cutting out. Its actually a design flaw in that these older boxes fail in the exact same way after a few years or so of use. The power PCB in the box literally cooks at a specific spot until the damage results in random power loss. The newer Kelmar boxes seem to work more reliably so far.