Film-Tech Forum ARCHIVE: Stereo Cell Alignment Issue-

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Posted by Bill Duelly (Member # 3612) on 02-20-2009, 08:26 PM:

I have a Sony DFP 3000 Processor, JAX light and stereo cell in a RCA 1040 sound head. When running Dolby Tone, the level on the right channel seems to bob up and down a bit, but the left channel seems fairly steady. When I think I have it up to an average level, and then put a reel on, it appears that the right channel could be a few hashmarks weaker. As it is, the gain diffrerence between the two is about 2.0 DB. Also as an FYI, it is aligned for minimal cross talk as well.

Could this be a sign of one side of pickup cell going bad?
(I also checked to make sure the lens optics were clean. Also, there is a new LED array in the JAX light so it shouldn't be that) Or could there be something else at play? Anyone else ever come accross this?

Posted by Monte L Fullmer (Member # 2797) on 02-20-2009, 08:32 PM:

you might have some oil in that slit lens that could be an issue.

Have an extra slit lens around to swap out and try?

Big problem with the Jaxlight on existing slit lens/photocell assemblies is that the lens and photocell originally work together to accomodate the full light spectrum of the white light from the exiter lamp.

The emissions from the red LED of the Jaxlight isn't strong enough to go through the glass elements of the slit lens and the cell isn't sensitive enough for red light frequency as for normal full spectrum white light. Thus, you're only getting half of what's needed.

-Good luck -Monte

Posted by Bill Duelly (Member # 3612) on 02-20-2009, 08:58 PM:

The only other slit lens I have is a wider mono one. I heard tell of opening a lens to clean it. Is it a difficult process?

Posted by Monte L Fullmer (Member # 2797) on 02-21-2009, 03:46 AM:

Sorry, can't answer that one on how one would take apart a slit lens assembly outside of sending them to your supplier who knows where to send them in for professional cleaning.

Posted by Marin Zorica (Member # 1716) on 02-21-2009, 04:57 AM:

First clean all optics including cell, I did have seen some small damage to cells but they still performed well.

Are this happened before or, maybe something is wrong with wiring or grounding on that channel?

Posted by Ken McFall (Member # 845) on 02-21-2009, 09:40 AM:

Jax lights are awful and very critical to align to get the most out of them. You may well find that the uniformity is.... will be, poor.

Get a loop of some CAT506 uniformity test film. Feed the left and right test signal from the processor into one channel of your analyser and feed BOTH left and right test signals from the processor in to it.

You should ideally see six peeks representing three signals on each channel from your processor. The aim is to get the peeks all the same hight so that the film is illuminated evenly across both channels.

You may find you have to shim the Jax light on the inside, outside, rear or front or a combination to get the best results possible.

As for you having a mono lens tube I'm not heard on one before. I'd give it a try and run some buzz track. You should be scanning to the maximum width without any signal from the edges of the sound track.

It's a time consuming job to experiment with different parts and having to re do the a chain each time but it may reward you with an overall better sound.

If all else fails dump the Jax light!!

Regards.

Posted by Gordon McLeod (Member # 33) on 02-21-2009, 11:27 AM:

I don't think one can take a slit lens apart
Put a scope on the output and see if the level fluctuation you are seeing is the dolby tone or background noise
then reverse the cell connection at the jax light preamp and see if the problem moves

Posted by Louis Bornwasser (Member # 3063) on 02-21-2009, 03:06 PM:

Many of the old B&L lenses unscrewed. I haven't unscrewed an RCA lens, but they are all build alike. Be sure to reseal!

BTW: the only good Jax lite is one in a museum, that is not powered up. Louis

Posted by Phil Hill (Member # 371) on 02-21-2009, 03:14 PM:

Why do so many people put down JAXlights? It seems like a viable solution to the cyan track issue.

I'm not particularly fond of their preamp... I think it sucks. But properly modified, it works great.

Please be specific in your pro and/or con comments.

Posted by Gordon McLeod (Member # 33) on 02-21-2009, 03:18 PM:

I believe that Ray Derrick made a modified preamp for them down in Oz
The Led source is by itself more than clever

Posted by Bill Duelly (Member # 3612) on 02-21-2009, 04:35 PM:

I did give things a thorough cleaning today, having to pull the lamp socket out to get to the back of the slit lens. When I put it back in, I had to readjust (raise) the levels. The right side still needed more gain, but it did seem more stable. We'll see.

BTW, I had also reversed wiring like Gordon suggested and it is NOT the pre-amp.

Posted by Bill Enos (Member # 440) on 02-21-2009, 06:50 PM:

Make one of Jeff Strickler's homebrew red led replacements. We made two of them and used them for 3 years without having to touch anything. They seem to be brighter than the Jaxlight and have a wider angle and covered the slit lens completely. They were eventually replaced by BACP reverse scans.

Posted by Kenneth Wuepper (Member # 1174) on 02-21-2009, 10:09 PM:

Bill,

Try looking at a Dolby installation for the A chain alignment. There you will find a simple way to "see" the light coming through the slit lens. Perhaps that will simplify your alignment as well as answering your question of coverage of the track.

In the CP-55 manual in the manuals section of this site you can see this process in the 4.4 section of drawings.

Hope this helps.

KEN

Posted by Monte L Fullmer (Member # 2797) on 02-21-2009, 11:58 PM:

Dang,forgot about that old 'paper trick' to see the filament display..that would work.

Posted by Bill Duelly (Member # 3612) on 02-23-2009, 09:02 AM:

Well those tips have offered some guidance to go further as well as jarred the memory. I may be on to the root cause of all things evil in this setup... A little history first to set this up.

About 10-12 years ago, the soundhead was at the old Rangertone to modify for stereo. The put a newwcell in, but for the narrower slit lens, they did NOT use one for the 1040 but took another on that was short & stubby. Doing so, they took off the tightening knob and put in a new lock down screw on the side. It is aslo apparent that they did some minor boring to that lense hole.

With the bright incadessent, there was always plenty of light to work. When the JAX went in, the short lens was NG for generating enough light. So I was able to obtain a proper slit lens. I installed and aligned using the scopes, but after contantly doing that, it never really seemed to hit the perfectly clear sound.

So after very careful study this past weekend, what had happened was that after I hit the right spot on the scopes, and then tightened, the tightening process (with their new set screw) was actually rotating the lens ever so slightly (changing azimuth) and with the wiggle room, was also shifting it horizontaly so it was giving weaker signal to the right channel area.

Sooo.. it will be some work to shim the lens so it won't shuffle in the next alignment. It at least looks like I may be on the right path. As always, gentlemen, thank you for your assistance!

Posted by Bob Koch (Member # 1062) on 02-23-2009, 03:01 PM:

The standard optic for the MI1040 can be cleaned. In the long ago I had operators that oiled the projectors as though they were locomotives. I had a little saw blade to remove the sealant from the back factor and it unthreads and exposes the slit assy which is easily removed.Used to clean it with a piece of scraped scrap film. front factor also can be unthreaded and cleaned. Used to reseal them with a mixture of litharge and gylcerine.With single screens and in my territories,where travel time was measured by hours,not miles, doing things like this were manditory.
Sounds like a really prostituted lens set up on your 1040. I installed lots of Dolby equipment before I retired but never saw anyone attempt to use a 1040

Posted by Bill Duelly (Member # 3612) on 02-23-2009, 07:59 PM:

Well, just finished 2 hours with it and it sounds like I am golden.

No hook on the azimuth display, some strips of splicing tape to shim...High freq seems in place (even after locking down.

Again, many thanks everyone, ALL suggestions helped me get my brain kick started to tackle this [Smile]