Film-Tech Forum ARCHIVE: Dolby Digital reader failing

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Posted by Stephen Frazza (Member # 2320) on 08-09-2012, 07:53 AM:

On a Dolby CP650 and a BACP digital reader I kept getting high error codes and then complete failure on different prints.
So I swapped out the reader with one from another house that I knew worked and I even swapped out the cat 773 in the 650 and still got the same problem.
When I hook up the alignment software I get vertical jitter errors.
I spoke to dolby and they say its the projector (Simplex XL) not pulling the film correctly.
Would this be an intermittent issue or is there something else it could be?

Thanks

Posted by Randy Stankey (Member # 64) on 08-09-2012, 10:09 AM:

The upper/feed sprocket pulls the film through the reader. It should insulate the incoming film path from the intermittent.

If that sprocket is jittery enough to boink the reader, you've got a really big problem.

Look at the system with an oscilloscope. That will tell you a whole lot more than DRAS will.

I bet you'll see the trace moving in and out like a wave.

Watch the scope while you look at the film coming across from the platter to the upper/feed roller on the projector. I'll bet you'll be able to see the oscilloscope moving in and out in sync with the film bouncing up and down.

A classic sign of not enough tension.

Check that the reader is properly threaded and the two spring loaded tension rollers are set properly.

Be sure the film feeding in from the platter has enough back tension on it.

A Kelmar film cleaner in the path before the reader, either on the projector or on the platter will also add some back tension and make the system read better, too.

Posted by Stephen Frazza (Member # 2320) on 08-09-2012, 01:40 PM:

Unfortunately I do not have a oscilloscope. It seems to have enough back tension and the film is not bouncing coming from the platter. The platter even has a tension fail safe on top of the pole on the platter. I even tried pushing down on it with a roller to create more tension but doesn't seem to help at all.
The reader I know works because it just came from a house that went digital and it was working fine in there.
I guess I'll have to look at the feed roller tomorrow.

Posted by Randy Stankey (Member # 64) on 08-09-2012, 03:21 PM:

If the upper feed sprocket in the projector which pulls the film in isn't running steadily, the whole projector won't work well.

The sprocket will either be making all sorts of awful sounds, you'll loose your upper film loop or the whole projector won't run steadily.

The DRAS software will help you keep a working system in tune but it will not be useful in fixing a system that doesn't work already.

Get a scope or find somebody who does. Hook it up and do a tune up from the beginning. During that time, if there is a problem with the CP650 it will become apparent.

But, if the reader isn't working, the whole thing won't work. And the reader won't work if the film isn't going through it right.

BTW: How about the flywheel on the reader?
Is it on tight and spinning smoothly? No "gravel" in the bearings, etc?

Posted by Tony Bandiera Jr (Member # 2365) on 08-09-2012, 03:47 PM:

Randy is very close but there are some errors with his statements. A problem with the upper feed sprocket generally won't affect the whole projector's stability, and it often won't make noises.

It is a good place to look first, make sure there are no missing teeth on the fiber gear, make sure the sprocket itself is tight on the shaft (the nut in the center isn't loose) and that there is no excessive play. (Check with the projector off, try to turn the sprocket back and forth by hand. Any more than just a tiny amount (about 1/8th of a sprocket tooth) of play is excessive.

But the upshot is that the projector is most likely not running smoothly. Some areas to look at:

If it's an older SH-1000 type soundhead, the intermediate drive gear between the projector and soundhead, loose, worn out or broken free of the bearings; internal bronze gears bad, bad motor coupling.

If a 5-Star (belt drive), bad belts (missing teeth or loose); bad bearings in the sprocket shaft of the soundhead; loose drive pulleys (the setscrews are notorious for loosening up and making the drive pulleys sloppy on the shaft..to check, hold the soundhead sprocket with your hand and try to turn the motor flywheel by hand, any slop is not acceptable). Loose pulley or flywheel on the motor.

Either type of soundhead: Bad motor (shorted windings, bearings, etc.) loose electrical connection to motor or bad contacts on motor relay in automation or switch.

Any of the above can cause vibrations/speed irregularities which will translate into vertical jitter.

Posted by Sam D. Chavez (Member # 1841) on 08-10-2012, 12:46 AM:

If this is a platter house, esp. AW3, check there first. Does it drop out more on one particular platter paying out? The springs that provide hold back tension are often the problem.

Posted by Stephen Frazza (Member # 2320) on 08-14-2012, 08:35 AM:

I'm still having issues. Its a 5 star soundhead. I changed both belts, tightened the drive pulleys, checked all the gears, the fiber gear is fine, there doesnt seem to be any excessive play anywhere - even compared to other similar working machines.
Oh and I swapped out the entire upper feed sprocket for a different one.
I pretty much tried everything everbody mentioned aside from a scope and swapping out motors(connections seem fine)

The platter is a strong DMC but I still dont think it's bounce coming from there.

Any other suggestions would be great. Thanks

Posted by Darryl Spicer (Member # 711) on 08-15-2012, 02:31 PM:

Could be cracks in the rubber of the damping roller that closes down on the film and the sound drum. The sound drum bearings may be starting to dry out causing some vibrations.

Posted by Tony Bandiera Jr (Member # 2365) on 08-15-2012, 05:25 PM:

Darryl, that would be the case if he had a basement reader...but I believe we are talking about a penthouse reader so your suggestion would have no effect. [Smile]

Posted by Monte L Fullmer (Member # 2797) on 08-15-2012, 10:42 PM:

Depends on how old the reader is. Can the current be turned up on a BACP, is does it simply require an LED changeout.

Even if not too old, there could be some LED arrays that have burned out in the beam itself. To find out: Get a piece of black film and fold it over on itself to look through while you looking at the main LED array to protect the eyes (like a welder's glass).

Here you can actually see the individual LED arrays in the beam - some use a single array and others use a double array. If any arrays are burnt out, it could cause read issues by the camera to cause high error count - meaning an LED replacement is in order.

Also, the lateral guide rollers on the reader could be off (or worn to one side) where the beam isn't center with the track on the film - why of the "o-scope" , or at least WinDRAS to check alignment.

Posted by Darryl Spicer (Member # 711) on 08-16-2012, 02:02 PM:

quote: Tony Bandiera Jr
Darryl, that would be the case if he had a basement reader...but I believe we are talking about a penthouse reader so your suggestion would have no effect.

Well, That's what I was thinking too Tony but then he posted this.

quote: Stephen Frazza
I'm still having issues. Its a 5 star soundhead.

Posted by Tony Bandiera Jr (Member # 2365) on 08-16-2012, 03:14 PM:

I see your point and you are right, but AFAIK BACP doesn't make a Digital Basement reader. [Smile]

Posted by Clint Koch (Member # 1179) on 08-16-2012, 04:45 PM:

The BACP DSTR-20 is the only version and it is indeed a penthouse reader.

Posted by Stephen Frazza (Member # 2320) on 08-16-2012, 09:32 PM:

It is a penthouse reader, a merely mentioned it was a 5 star because Tony posted about a 5 Star or SH-1000 sounded.

And the reader I swapped in just came out of a house that went digital and it was working fine in there. That is why I don't think its the reader. But at this point I don't know what else to check.

Posted by Monte L Fullmer (Member # 2797) on 08-16-2012, 11:07 PM:

Do this trick: find a brand new trailer, cut a length from the trailer to make a good sized loop to thread through the reader and the entire projector and turn it on.

See what the error rate does. If your error rate suddenly drops, I then blame the print (or your platter is scratching up the data section of the film and this will definitely cause dropouts), then do a print swapout with another print to see if the problem follows.

Good luck - Monte