Film-Tech Forum ARCHIVE: Dolby Cat 701 roller and guide adjustment

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Posted by Frank Dubrois (Member # 3042) on 02-01-2007, 06:36 PM:

How are the rollers or guides adjusted for tension? I think our guides have too much tension on the film causing it to go into failure. I have looked at the manual, and see a couple arms inside the cat 701 unit that look like they can be adjusted, but I was wondering which screw to loosen for the adjustment, and do I have to adjust both arms, or just the one I suspect is causing the problem. Any help would be appreciated. Thanks!

Posted by Louis Bornwasser (Member # 3063) on 02-01-2007, 06:41 PM:

You absolutely MUST have enough film tension to positively lock the film on the drum. With slippage you get faults and film damage. Louis

Posted by Frank Dubrois (Member # 3042) on 02-01-2007, 06:55 PM:

Is there such a thing as too much tension? I noticed a film playing with an error rate that went from 5 to F or from 4 to F or from 7 to F, but when I lifted the upper arm, the error rate stayed around 4. It made me think that possibly there is too much tension on the film.

Posted by Mark Gulbrandsen (Member # 72) on 02-01-2007, 07:00 PM:

Frank,
Assuming this is just a normal wear thing.... You either have a worn lateral guide roller(the one with flanges) or low video level... or both. A worn lateral guide roller is easy to spot... look for a raw alumnium edge...usually the inner edge opposite the sound track. It sticks out like a sore thumb. This allows film to weave back and forth sometimes going out of range of the CCD sensor... so when it drifts back in you get a pretty low reading and when it drifts out of range you get an "F". Simply installing a new roller brings them back spot on every time... at least when someone else hasn't tinkered with them. ALSO... If you remove the flanged lateral guide be sure not to loose the spring washer and spacer washer that are behind that inner bearing on the roller! They tend to stick to the bearing and then drop off on the floor.

Naughty Frank...! What ever you do don't mess with the tension or back side lateral guide adjustments. You'll have to return the reader you tinkered with to Dolby to have it properly re-set. Setup your at least 60mhz scope and laptop in the appropriate manner and diagnose it properly!!

Mark

Posted by Frank Dubrois (Member # 3042) on 02-01-2007, 07:53 PM:

quote: Mark Gulbrandsen
Naughty Frank...! What ever you do don't mess with the tension or back side lateral guide adjustments.

I didn't. I looked at it, and thought I better ask before touching anything back there. i will look for the worn parts.

Posted by Cameron Glendinning (Member # 3516) on 02-01-2007, 11:08 PM:

quote: Mark Gulbrandsen
or low video level...

Every now and then you have to replace the bulb, has it been changed recently?

Posted by Frank Dubrois (Member # 3042) on 02-01-2007, 11:52 PM:

The LED is new. There is no consistant error rate with this unit. It can play fine for a part of the movie, in the 3's or 4's, then all of the sudden goto F for no apparent reason. This has happened for several different movies we have had there.

Posted by Mark Gulbrandsen (Member # 72) on 02-02-2007, 09:13 AM:

Setup your at least 60mhz scope and laptop in the appropriate manner and diagnose it properly!!

Posted by Monte L Fullmer (Member # 2797) on 02-02-2007, 09:54 PM:

...Yeppers, like I gotta do with 14 CAT-70x units in my area - replace all 14 sets of rollers that I just received from Dolby.

Each of these units have badly worn upper lateral guide rollers with raw, sharp-edged metal flanges to where one can easily move the film across the drum to get a good error count and stop the "4 to F" readings.

quote: Mark Gulbrandsen
If you remove the flanged lateral guide be sure not to loose the spring washer and spacer washer that are behind that inner bearing on the roller! They tend to stick to the bearing and then drop off on the floor.

...and make sure that you have the right sized snap ring pliers to take that snap ring off that holds all of this on that shaft...and be careful because those snap rings love to disappear when they fly off the tips of the pliers when not properly seated on the tips..

- Monte

Posted by Frank Dubrois (Member # 3042) on 02-04-2007, 12:53 AM:

How long is a set of these rollers supposed to last? Any clue as to how expensive a set of rollers are? also, I'm curious if the washers and end clips are something a hardware store might have? I think they were 1/4" washers? One flat, one curved and then the end clip.

Posted by Monte L Fullmer (Member # 2797) on 02-04-2007, 03:33 AM:

quote: Frank Dubrois
How long is a set of these rollers supposed to last?

..it's all related to the user on how he takes care of things.

If a user doesn't use the proper gap space inbetween the two rollers and let the rollers run on to each other while the film is in motion for a week, it pretty well toast for these rollers.

Yet, what is good is that if the gap collapses like if a bad splice or something to let the film jump off of the large register sprocket, one just opens up the upper roller, pull on the film slightly to back the film one sprockettooth and then close the assembly,while the film is still in motion, this allows the proper roller gap to be reset. Done this trick many times.

Granted, when the film runs out of the assembly, the rollers do snap into each other, thus there is actually no total preventiveness in this snap closing technique..unless the user is right there when the film runs out to catch this assembly before they snapclose, then they can last quite the long time.

-Monte

Posted by Monte L Fullmer (Member # 2797) on 02-07-2007, 03:17 AM:

UPDATE: After doing a roller changeout on 14 readers, the error count drastically changed from between 7.5 and F, clear down to a good solid 5 on majority of some readers.

.. and I did get some 1.5's to a settled-in 3's on rare occasions with some other readers.

Posted by Mark Gulbrandsen (Member # 72) on 02-07-2007, 03:13 PM:

Thats still pretty high if you ask me. 1. to 3. would be normal for new film with some running at 1's and 0's these days. I think you just need to fine tune your technique.

Mark

Posted by Monte L Fullmer (Member # 2797) on 02-07-2007, 09:20 PM:

Oh, I do agree with you Mark, but when most of these houses run used film, one can wonder on how the condition of the prints.

thx-Monte

Posted by Frank Dubrois (Member # 3042) on 02-13-2007, 01:03 AM:

didnt fix the issue...

Posted by Monte L Fullmer (Member # 2797) on 02-13-2007, 06:17 PM:

...then, you need to get a tech over there and have him look at the readings via scope, for you could have LED's that have simply reached tired status, scanner drum bearings have reached their useful life, or an alignment issue is in store.

(How about the camera lens, have you cleaned it to ensure to capture all of the brightness from the LED?)

Posted by Gordon McLeod (Member # 33) on 02-14-2007, 08:49 AM:

I think the most important advice was missed that mark said hook up a scope
Also dras will tell you in the jitter reaqding a lot about how well the damper is working

Posted by Frank Dubrois (Member # 3042) on 05-20-2007, 03:21 AM:

quote: Mark Gulbrandsen
Thats still pretty high if you ask me. 1. to 3. would be normal for new film with some running at 1's and 0's these days. I think you just need to fine tune your technique.

How do you fine tune installing a roller? Or were you talking about the scope/laptop set up? I thought the adjustments on these things were strictly "by the numbers" types of adjustments. By that I mean, the last time I watched a tech fix a dolby reader, it whipped out his scope and laptop, adjusted it according to proceedure, and left. He didn't test it, he didn't go down and listen to it. We got an error reading of about 5-6 with a new LED and new rollers. Not very fine tuned if you ask me.

Posted by Mark Gulbrandsen (Member # 72) on 05-20-2007, 07:52 AM:

quote: Frank Dubrois
We got an error reading of about 5-6 with a new LED and new rollers. Not very fine tuned if you ask me.

Did you call the tech back in after you saw it this high... or was this some other place you were at? What film did he use to align the reader? Perhaps the film being run at the time was this bad, it happens. Best thing to do is watch a brand new trailer pack and see if it stays high or varies a bit up and down. Too high of video level can aleo result in higher error readings I've only had one dashpot fail and one scratched light pipe in a cat 700 over the years that caused strange problems. Installation of a new lateral guide roller and led sets em straight 98% of the time. The other 2% of the time you might have bad bearings or a bad dashpot. I aloso once had a factory new CAT 701 that had the spring washer missing from behind the roller. This penthouse played back inconsistantly high and then low error rates sometimes in the same reel of film. Did you replace the LED with a factory mount assy or just the led or not at all? How did you align it?

If yours was "messed with" then sending it back to Dolby for service will set it perfectly straight again.... that is if you don't trust your local tech. Donno Frank but you seem to drag these simple technical problems on and on and on. Is anyone still comming to your theater any more? And what about your avitar photo? YYou've been on here for years now and STILL no photo. I think Brad should cancel your subscription until you send in your photo.

Mark

Posted by Steve Guttag (Member # 268) on 05-20-2007, 11:27 AM:

One can't judge the error numbers on a print...depending on where the print was in the run, the quality of the recorder and its alignment...the reader being used to judge the film and its alignment as well as lens all factor in.

I have readers that will track in the 0s on some films and 5-6 on others...often one can see a noticable change between previews as well as previews to featres. I've had features where the azimuth jumped from 0 to -12 on bad reels...it showed up as much higher error rate and dropped blocks.

Despite Mark's 60MHz statement as slow as a 20MHz scope can be used very effectively. However, the faster scopes allow one to see things more clearly, for sure. The 100MHz Tek scopes we use were a marked improvement over the scopes we had been using though we were able to use the slower scopes with identical results...it just took a wee bit longer to judge if we were in the sweet spot.

The CCDs and lenses have changed as have the models...the latest units (like the Cat 702s) have faster lenses as well as the higher density CCD which made focus much more critical since the depth of focus is so shallow. Again, different reader brands will react differenty since different lensing is used.

We bought our test film in bulk and had it measured...thus we know where its azimuth and lateral alignment is...we also noted the best focus that could be achieved with it via DRAS using the white light readers (Cat 699 and Cat 700)...it was rather interesting to note the differences that ensued as it was checked on Cat 701s and Cat 702s (or BACP DSTR-2000) as well as Kelmar and CE basement readers.

Note the dash pots can certainly be adjusted in the field...you just have to know what you are doing and what you are looking for. They can even be more precisely optimized for the film transport system you have.

Mark is definately correct that excessive LED level will take away from the error reading...With an LED based reader, going above 4Vp-p doesn't buy you anything (4.5Vp-p on a white light reader). Going above 5Vp-p on any reader will start to clip the signal and increase errors.

A quick fix (though not permanent) on a Dolby penthouse reader for the lateral guide roller is to rotate it around. More often than not the film has been biased to the inboard side and has worn the aluminum away to the point the film is no longer laterally centered. Rotating the roller around will buy you some time until the new rollers arrive.

Steve

Posted by Frank Dubrois (Member # 3042) on 05-20-2007, 03:01 PM:

quote: Mark Gulbrandsen
Donno Frank but you seem to drag these simple technical problems on and on and on.

I'm just looking to get it solved, that's all. I didn't know that aligning a Dolby penthouse reader was so damn easy, wow, I feel so stupid. Although I appreciate your help, you simply must understand that not everyone knows everything there is to know about projectors. It's an ongoing learning process for me. [thumbsup]

Posted by Brad Miller (Member # 2) on 05-20-2007, 03:14 PM:

quote: Steve Guttag
I have readers that will track in the 0s on some films and 5-6 on others

5-6 Steve? Ok then I am officially lucky when it comes to SRD. 0-3 is what I see all the time. Every once in a blue moon I see a 4, but I haven't seen a 5 in.....heck, forever!

Posted by Mark Gulbrandsen (Member # 72) on 05-20-2007, 03:34 PM:

quote: Steve Guttag
Despite Mark's 60MHz statement as slow as a 20MHz scope can be used very effectively.

Definately! The 60mkz minimum I reccomend is mainly for easier triggering of the waveform. Its sometimes very hard to get a low bandwidth scope to trigger on a very fast leading edge where you want it to trigger. Higher bandwidth scopes are much mroe capable in the triggering realm. The 100mhz Tektronix stuff excells at it and I generally don't even need to use the clamp signal to trigger the video waveform.

Frank, I definatley reccomend you get a decent scope and laptop and a dightal cemera and post photos here of your waveforms. We can certainly provide you better assistance if you do... otherwise its a guessing game.

Mark

Posted by Mark Gulbrandsen (Member # 72) on 05-20-2007, 03:36 PM:

I've never seen tracking as high as 5-6 on new prints either and rarely on used prints... 4 is about the highest I ever see any more. I used to see this high number stuff
when about 5 to 6 years back and mostly i Idaho and Montana.
The bad thing about high error rates is that it really mankes the error correction system work very hard... this is true in any digital playback scheme... and this can actually degrade the sound somewhat. Lower is much better.

Mark

Posted by Steve Guttag (Member # 268) on 05-20-2007, 04:59 PM:

Yep...5-6 on even genuine Dolby Readers and even BACP. However, these same readers will track down to 0 on films that let them.

Another thing that will get you higher error numbers is having the track magnification wrong. You can get away with 101% but at 102% you will see the numbers climb...get to 103% and you will be getting block errors too. The same is not true for going below 100%...97% is not fatal.

What is going on when the system scans the film is to locate the 4 corners (they are unique blocks)...once the corners are located, the system knows what the corrective magnification is as well as azimuth/lateral postion. It then superimposes its grid over the bits and reads them. However, too "big" a picture is harder to locate the corner than too small. Rapid bouncing also will make its life harder.

As for error correction versus sonic quality. It has been my understanding that Dolby's error correction restores the signal 100% such that a reader tracking "0" will sound identical to a system tracking solid "8" (with no block failures).

An indication on DA10/20 and CP500 systems of how hard the decoder is working are the column of LEDs on the Cat 671 cards (two locations). The top 4 LEDs in each column (4 columns total) really tell the story on the reader. If they are steady, the reader is alinged reasonably well (not that it can't be improved). What these four LEDs (in all four sets) indicate are if the reader was able to locate each corner on the 1st scanning pass. If one of the LEDs is out or always flashing (you will find it flashing in that case on all four sets) then the reader is not aligned too well since it is constantly missing that corner of the digital block on the first pass). I believe the DA20 makes about 256 scans (I could be very wrong on that one...the number is from memory) and if the system was able to locate the corner on ANY pass then it is represented by the bottom for LEDs (in each set). So if the system gets all four corners on the first pass, it will have the easiest time determining what the position of the whole block is (And magnification) in order to compensate for printing/scanning difficulties.

As to scopes...I have/had a Heath Scope that I used and it had a really nifty ability to LOCK on a signal. It was real handy in the forward scan days using Cat.97...you rotate that knob (after getting the trigger level right) and BANG it was rock solid without flicker and jumping about. It was only a 20MHz scope (I bought it around 1984 or so). It beat a 40MHz Hitachi scope bought about 12 years later. But the 100MHz Teks...well that is like coming in out from the cold...nice crystal clear images. In fact, I use my Tek to do some video work that really a 300-500MHz scope would be more appropriate for (I use a signal that doesn't tax the 100MHz limit but tells me what I need to know)...it is amazing how much better a video picture can be when you get the level and HF correction right (analog systems). It is to video what the solar cell preamp and slit loss is to the A-chain of an optical soundhead. Why SDI (and now HDSDI) didn't catch on for A/V grade video is beyond me. One cable instead of 5 and so long as you keep within its range, the picture is the same at both ends (and to extend the range...reclock and deal with the latency). Even for the home...HDSDI would have been so much better...one cable and it can even carry audio (and its range is about 300-feet!).

Okay...I've drifed off topic (again)...sorry.

Posted by Mark Gulbrandsen (Member # 72) on 05-20-2007, 05:10 PM:

There's an old Heath scope kicking around at work if you want it I can send it to you. I think its an IO-46 something or other. The ability to see the "hair" which is the digital data on the video waveform with a high end scope makes focus so much easier... especially on Sony's stuff.

FWIW: I typically see one error number less on a BACP penthouse than Dolby and then one more number less on a 650 than a DA-20 or CP-500 on any given print. The Christie basement readers work great on the Cine-X35 projector with error rates as low as zero. Christie has decided not to pull that projctor from production just yet.

Mark