8mm Forum: optical sound problem on ST1200HD

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Posted by Eric Baucher (Member # 809) on May 16, 2008, 08:20 PM:

I finally got an optical feature, put it on and I get no sound. mag sound works fine, the exciter lamp is lit but sound is VERY VERY low. only on the loudest parts of the soundtrack can you detect any sound. whats wrong? I was happy to have an op feature finally.

Posted by Kevin Faulkner (Member # 6) on May 17, 2008, 06:03 AM:

It could be many things but first, without film running through the machine but with it switched to optical do you get a loud thudding noise if you put a bit of paper between the optical lens and lamp. (push paper in and out to break beam of light).

Kev.

Posted by Maurice Leakey (Member # 916) on May 17, 2008, 06:13 AM:

Kev

In one cinema I worked in we used to do just that. First thing in the morning afer switch on it was to check the two soundheads. This was in the days of 2000' spools and changeovers.

But we only did it if the Chief wasn't around. He swore that it would damage our auditorium speakers.

Posted by Barry Johnson (Member # 84) on May 17, 2008, 07:54 AM:

And quite right too.
Being a retired Chief Projectionist,I took the same stance.The reason is because interrupting the light beam and causing a 'blip' accellerates the cones within the speakers and can,damage or even destroy them giving you distorted sound after the event.With the power driving large auditorium speakers it happened quite easily.Especially if using high powered power amps.Dont do it.

Posted by Joerg Niggemann (Member # 611) on May 17, 2008, 09:25 AM:

Do it, but at low volume ;-)

Posted by Jan Bister (Member # 332) on May 17, 2008, 08:34 PM:

*chuckles* this happens to remind me of a piece of techno music I have somewhere on an old cassette tape, it goes something like this:

(club dance beats)

"THIS SHOULD BE PLAYED AT HIGH VOLUME"

(more beats)

"PREFERABLY IN A RESIDENTIAL AREA"

[Big Grin]

Posted by John Whittle (Member # 22) on May 17, 2008, 11:16 PM:

As Kev said, it can be many things. Doing the paper test will tell you if the projector alone is producing enough light and the solar cell or other pick up is working.

Beyond that, there can be problems with the print or projector. Since prints fade and if the print was not "applicated" then as the cyan dye fades, the film doesn't hold back as much light as it should. Alternatively it can be either an electrical or mechanical problem in the projector. If the thump test works and several prints exhibit the same problem but the color isn't faded, then you could have an amplifier problem, bad solar cell or optics out of alignment. Or the print might not be guided properly past the scanning lens.

The tolerances on Super8 are so small that any thing off of perfect results in some problem from slight distortion to no sound at all. If it reads too far on one side then you'll hear noise from the frame lines, etc. If too far out, then nothing.

To focus or align the optics you need special test films which are made for focusing and alignment. Don't try it without them, you'll invariable wind up the weeds and have to send the machine off to someone with the proper equipment.

John

Posted by Eric Baucher (Member # 809) on May 18, 2008, 07:06 PM:

thanks for the help. Did the paper test, got nothing, then when I flipped the switch back to mag, that didnt work for a few mins till I moved the switch to optical and back again, then the mag sound came back again so I think it could be the switch. so where do I go from there?

Posted by Paul Adsett (Member # 25) on May 18, 2008, 08:00 PM:

I have to agree with John's comments about trying to align the optical lens assembly by yourself. The particular design of the mount for the optical relay lens assembly does not garner any praise for the Elmo designers. To put it bluntly it is awful. Instead of designing precision X-Y adjustments for the optical track lens, Elmo pulled the same stunt that they adopted for the main projection lens mount, that is oversize holes for the mounting screws, which completely eliminates any precision convergence positioning of either of these optical assemblies. They are both literally squirmy hit and miss adjustments.

Posted by Josef Grassmann (Member # 378) on May 21, 2008, 03:26 PM:

be carefully with adjusting optical lens.
I wouldn`t recommend it. In most cases it becomes worser than before. A optical lens will not move out of focus during whole life of any projector.
Look behind small rubber roller with a small torch. There should be visible the silicon chip about 2.5mm (1/10")long from the grey plastic holder.
If difficult to see, remove small philips screw and draw off the rubber roller. We got some St1200 for repair where the silicon chip has been broken off. The silicon chip ist "free standing" and approx. 0.5mm thick and extrem brittle. Take greatest care when cleaning. Watch whether light from exciter lamp hits the silicon chip, darken room if ness.

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