Film-Tech Forum ARCHIVE: Film skewing in RCA 1040 soundhead

This is topic Film skewing in RCA 1040 soundhead in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Christopher Seo (Member # 7) on 06-23-2003, 07:10 PM:

Hello all,

I've got a problem, apparently with only one of the RCA 1040s at work. Occasionally the film will somehow get skewed such that the Lt track drops to nearly nothing. I have verified this on both stereo and mono films with an oscilloscope in X-Y mode. Gently tugging on the film as it exits the (Century C) projector holdback sprocket restores the Lt-Rt balance. I have verified correct lateral alignment/levels with Cat. 97 and 69T.

I haven't caught it doing this enough times to determine whether it's happening at a splice, or what. However, the film looks well-seated, the lateral guide roller spins freely, and the spring-loaded flange seems to move freely as well. Nor does the film make any unusual noise when it skews around. However, I have noticed that small deviations in X-Y plot angle (from 45 degrees) correlate to an increased buzzing sound coming from somewhere in the soundhead film path.

Any explanations/suggestions would be much appreciated. I don't know if this is a new problem with the soundhead since it's not noticeable in the booth, but definitely noticeable in the auditorium as the left channel drops out and center shifts to right!

Edit: After playing around with some old trailers, I do see that the soundhead lateral guide roller can be made to pinch the film, and the film will stay pinched until it is pushed back into place. Is there a way to adjust the stiffness of the spring-loaded flange?

[ 06-23-2003, 08:15 PM: Message edited by: Christopher Seo ]

Posted by Mark Gulbrandsen (Member # 72) on 06-23-2003, 08:16 PM:

Be sure that the lateral guide/impedance roller casting is not bent, or cracked and running at a slight angle. This is VERY common on Simplex 4 star sound heads, and could happen on an RCA as well and these old die castings can be fragile. This would easily cause the film to skew to one side and sit there. I've seen 4 star sound heads in which the film wouldn't even stay in there at all...... It walked right out of the scanner.

Also check bearings, impedance roller, and all parts associated with that section. Replace anything thats worn.
Mark @ CLACO

Posted by Gordon McLeod (Member # 33) on 06-23-2003, 08:19 PM:

often it is too much side tension from the spring on the flange of the roller causeing the thinner estar stock to buckel

Posted by Paul G. Thompson (Member # 655) on 06-23-2003, 08:40 PM:

In addition, make sure the cushion roller is not stuck. Also if I recall correctly, one of the lateral guide flanges is spring loaded. When you push on it, it should snap back when you let it go. If it is stuck or does not snap back, chances are someone was using too much WD-40. It will jam those things up quicker than a bumble bee getting smashed in your face when riding a motorcycle.

Also check the alignment of the CS sprocket in the soundhead, as well as the holdback sprocket in the projector. The holdback is probably not out of alignment, but with that fruit-cake way the projector bolts to the 1040/1050, the whole projector could be "cocked" by a couple of degrees or so. Grab ahold of the projector head and give it a twist. If it moves, you probably found the problem. Re-align it and tighten down the bolts with a wrench you don't have. I had to make a wrench to fit by grinding it down on a grinder. (actually, a tappet wrench will probably fit...if you can find one....)

Posted by Don Sneed (Member # 955) on 06-23-2003, 09:26 PM:

see if the sound drum moves in/out, I have seen this same thing cause by the sound drum moves causing the drop out...

Posted by Paul G. Thompson (Member # 655) on 06-23-2003, 09:40 PM:

....or the rotary stabilizer dragging on the cover of the gear side of the soundhead. If it is, stuff some washers into the bolt-up pattern of the cover.

Posted by Sam Hunter (Member # 1119) on 06-23-2003, 11:00 PM:

I had that problem when I first got my 9030. I found that the lateral guide needed a good cleaning out. Gave it a good cleaning and replaced the roller and haven't a problem since.

Posted by Richard B. Perrine (Member # 409) on 06-25-2003, 09:48 AM:

We've had the problem here with the casting and the bearing.

One bearing is fixed and keeps the laterial guide rollers and the shaft in place. However, I've found several soundheads 1040 and 9030.....that the casting changes or expands....allowing the bearing and shaft to shift in and out slightly. this is independant of the adjustments for the buzz track....and annoying when it hits a splice and the shaft shifts position andstarts scanning the timecode or the sprocket holes.

Our solution was to disassemble the laterial guide roller assembly....taking out the bearings,shaft and rubber roller....the drill a very small hole and tap the casting for a screw to hold the bearing in place.

RBPerrine@aol.com

Posted by Bob Koch (Member # 1062) on 06-27-2003, 07:18 PM:

Try all these suggestions as any one of them could be the cause.
Many years ago, when working for Photophone, I had a 9030 that would do this and I tried everything including many of the above and I really had a caustic projectionist on my hands. Finally replaced the stud that screws in the frame that carries the lateral guide roller assy and this did it. Must not have been parallel to the drum or something. I was so damn glad to get it corrected I never investigated further.