Film-Tech Forum ARCHIVE: Dolby Digital Alignment

This is topic Dolby Digital Alignment - Cat. 701 in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Manny Knowles (Member # 1171) on 07-16-2003, 08:53 PM:

Okay I now have TWO Cat. 701 readers that are tracking F-F-F (CP500) and 7.-F-F (CP650).

One of them seems to need a new LED which I have and will install tomorrow (have to fly over there). The other reader (with the CP650) is less than a year old.

I ran a 69T loop and monitored the results on my oscilloscope. Everything seems fine. In fact, I got 5-5-F while reading the loop. Some of the trailers on the movie played fine and then the movie came along and crashed again (reverted to analog). So I'm thinking that the print is damaged.

Sidebar...The movie in question was SINBAD which, as I noted in another thread, was shedding. I used FilmGuard on it and instead of getting 7's and F's I got 6's and F's but it still reverted to the analog track. Oh well. Can't win 'em all, I guess.

While I still had the oscilloscope connected -- and running the test loop -- I tweaked the focus of the reader back-and-forth and the best I could get was that same 5-5-F that I had in the first place.

Two questions --

(1) Is a 5 really the best I'm going to get on that system? Currently the best I am getting is a solid 3 on another system of the same age. They were installed one day apart.

(2) I know that some digital LCD scopes are inappropriate for this type of alignment but why is this? My scope is a Tektronix 220 (not sure about the number but I think that's it). The only trouble I had was that the display did some funky stuff while I was adjusting the focus...but, then, I have to say I don't know if that would've happened on an analog scope.

BTW, an analog scope is on the way. A loaner from a friend in Florida. In the meantime, any tips, advice, observations and general discussion on the topic would be greatly appreciated...

Posted by Greg Mueller (Member # 17) on 07-16-2003, 09:18 PM:

Don't know if they're the same or not, but I had a 700 that wouldn't read (at all) until I adjusted the lateral guide roller, then it worked fine. The guide roller adjustment on the 700 is the worst design I can imagine. You have to practically disassemble everything to make the adjustment. Really poor design engineering.
Anyway, maybe you need to adjust the lateral guide roller

Posted by Mark Gulbrandsen (Member # 72) on 07-16-2003, 09:25 PM:

Greg,
You don't adjust the roller....You laterally shift the entire video pickup card in the rear of the unit.......
I've seen dozens of 700's and 701's wear this way...not at all uncommon.
Mark @ CLACO

Posted by Gordon McLeod (Member # 33) on 07-16-2003, 09:51 PM:

The reason LCD scopes don't work for alignement is at best they don't update the display fastenough to allow for mechanical movements of the device you are aligning
Have you used the Dras program to check for jitter?
Also how centred was the data blocks between the perf and what was the video level reading

Posted by Manny Knowles (Member # 1171) on 07-16-2003, 10:01 PM:

Interesting about the lateral adjust. Will try that.

The reading on the video level was 4V.

Gord -- about the update speed...is this why I still had a reading for a while after the motor had stopped?

Not sure what you mean about centered data blocks -- you mean "eyeball the print" or you talking about something I should be looking for on the scope?

Posted by Greg Mueller (Member # 17) on 07-16-2003, 11:22 PM:

Mark
Yes, you can adjust the lateral guide roller.
You have to take off the back cover and flywheel and spring. Undo the clamp screw (upper arm) and turn an allen headed bolt which moves the lateral guide roller in and out against a spring on the shaft on the outside. It's the only physical adjustment in the film path. If you read the DA20 manual it's documented there in Section 3 (3.5 "Film Path Alignment") In this particular case the guide roller had been "adjusted" in so far that the film was hooking on the sprocket teeth and buzzing as the film went through. Looking at the film on the sound drum you could see that the digital field was inboard of the sound drum maybe .010
After adjusting the lateral guide roller the buzzing went away and the unit performed fine.
Before adjustment it would not go into digital. Afterward it worked fine. Again this is for the Cat 700 and I don't know if it's the same for the 701/702 or not, but it sure is clunky

Posted by Mark Gulbrandsen (Member # 72) on 07-29-2003, 08:47 PM:

Greg,
Yes, that is an adjustment available on all CAT series penthouses and should really be set with a height gauge to the same height as the other rollers flange...... Using a height gauge in the booth is not generally possible so following the manual will get you close enough for it to work. Oddly this not a normally needed adjstment unless replacement of the roller or disassembly of this part has been done for some reason. The rollers do wear a bit over years.
Mark

Posted by Greg Mueller (Member # 17) on 07-31-2003, 09:29 AM:

Yah I read that part. I just adjusted it until the film's sprocket holes were centered around the sprocket teeth. It runs smooth and quiet now. An adjustment that is not often needed, but handy if needed

Posted by Jon Bartow (Member # 241) on 08-02-2003, 06:58 AM:

Manny, look at the Component Eng STRD30C manual. It gives good, detailed instructions for what to look for, etc. when aligning a Dolby Digital reader (basically it has good pictures which the Dolby manuals are missing) Gordon is refering to the "X1" and "X2" measurements i.e. lateral position. Use a scope and the DRAS software at the same time. The 700 should be able to read better than a 5 with a good PRINT not with a loop of test film. With a loop, even with FIlm-Guard the best I've ever been able to get is a 4. (That reader then tracked a 0. with a print later that same day)
Good luck!
Jonathan

Posted by Manny Knowles (Member # 1171) on 09-30-2003, 12:11 AM:

For those of us who need closure:

An alignment of the SRD head solved this. Now tracking as low as 2 but sometimes as high as 4. I'm happy. [Smile]

Posted by Jack Ondracek (Member # 1466) on 09-30-2003, 12:17 AM:

Manny...
Make sure the temperature at the pickup is no more than 42 degrees F, there's plenty of ice over the cold plate and the gas pressure at the rollers is around 100psi... it'll work fine.

... wait... wrong thread... sorry! [evil]

Posted by Manny Knowles (Member # 1171) on 09-30-2003, 11:07 AM:

You may know a lot about making good fountain soda but you don't know JACK about sound!!! [Big Grin]

Posted by Matt Zeiner (Member # 1914) on 09-30-2003, 12:30 PM:

I got a good tidbit from Lonny before he left Dolby regarding measuring jitter. I was working on an Ernemann basement reader and both DRAS and my scope were telling me that everything should be fine - yet it was still faulting out. As it turns out, with some types of jitter, the DRAS program can be fooled into "thinking" that there is no jitter, when there is. He told me to check the right-hand clamp signal (goalpost on the right of the display) - the jitter was perfectly visible there. Apparently someone had replaced the main drive belt and installed it inside out (an easy mistake and not so easy to spot) and tightened the crap out of it causing rapid jitter in the soundhead...I don't know how long it was running that way, but Im sure that there may be a few bearings in that machine that will need replacing soon - whoever changed the belt must have used a pry-bar to tension it [Roll Eyes]

Point is - all jitter should be clearly visible in real time on the right-hand goalpost.

Posted by Manny Knowles (Member # 1171) on 09-30-2003, 01:47 PM:

Something that I mentioned in another thread -- but it bears repeating here in case someone is reading this later on after doing a search:

Turns out that the Dolby test films will give high error rates (around 5) even when the head is aligned properly.

I've taken to using trailers now.