Film-Tech Forum ARCHIVE: Tech Needed

This is topic Tech Needed in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Robert E. Allen (Member # 1351) on 12-12-2013, 09:55 PM:

Hey Guys: I've got a hum in my sound system and I can't figure out why. Besides I'm an operator not a tech. Can you recommend someone for Eastern Oklahoma? We're a 35mm house.

Posted by Paul Maxon (Member # 6211) on 12-12-2013, 10:29 PM:

Is the hum present when the projector is running, or at all times? Im not a super skilled tech, but one of my screens at a second run house needed a new cable ran for the optical reader because it was getting interference from the motor.

Posted by Robert E. Allen (Member # 1351) on 12-13-2013, 01:29 AM:

Good point and I honestly don't know. We notice it only when the machine is running. Mostly on the right channel. But we just put the new print of "Hobbit" on and it seems to be in the left.

Bob

Posted by Louis Bornwasser (Member # 3063) on 12-13-2013, 06:06 AM:

Is Ben Kehee still active??

Posted by Leo Enticknap (Member # 534) on 12-13-2013, 06:10 AM:

Very obvious question, and apologies in advance if it's too obvious: is the hum only there when you're running film? Is it present when you're playing a CD as the audience comes in, too? If turning off the power supply to the optical sound exciter lamp and pickup altogether while a film format (e.g. 05) is selected on the CP gets rid of the hum, then the problem is with the A-chain. If that doesn't, but selecting a different format on the CP (e.g. non-sync) does, then the problem is probably in the circuits within the CP that process the signal coming in from the optical sound pickup on the projector. If the hum is still there when you're playing a CD, then either the problem is one in the CP that affects its entire output, or somewhere else.

Have you put any new item of electrical equipment in the booth recently (especially one close to the cable run from the projector's optical sound pickup to the CP)? If so, try unplugging it and seeing if the hum goes away.

If the hum is in the A-chain or the CP, there are several different things it could be, and a tech on the ground is really what you need. My instinct would just be to rule out the simple possibilities first.

Posted by Tony Bandiera Jr (Member # 2365) on 12-13-2013, 12:46 PM:

Critical info right here:

quote:
... We notice it only when the machine is running. Mostly on the right channel. But we just put the new print of "Hobbit" on and it seems to be in the left.

The problem appears to be that the lateral guide roller is out of alignment....if you're running in normal optical and not Dolby Digital.

Main cause will be that QC of prints is non-existent, and I'll bet that if you could compare the optical track of the Hobbit print to a test loop you'll see it's not aligned properly. Or there is some other issue with the print's optical track.

I no longer have any test films to spare or I'd send you a loop of buzz track and CAT 69T to check the soundhead with. Maybe someone on here can help out with loops if you don't have any.

You can, if you are careful, SLOWLY turn the lateral guide adjustment on the soundhead while the film is running, listening very carefully so that you stop as soon as the hum goes away. It should not take more than 1/4 turn in either direction on a Century or Simplex soundhead. (Any more than that can really throw things out of whack.)

The above is an easy test and MAKE SURE you somehow mark the original position of the lareral guide adjuster before you start so you can put it back if the 1/4 turn either way doesn't help.

Posted by Scott Norwood (Member # 30) on 12-13-2013, 12:59 PM:

Robert--if Tony's suggestion turns out to be correct, let me know and I will loan you the relevant test loops so you can re-align everything properly. With the correct test films, you should be able to do the lateral guide alignment fairly well by ear and the Dolby tone alignment with just the processor and a small screwdriver.

Do you have only one projector, or can you try the same reel in the other projector to confirm that the issue is not with the print?

Posted by Robert E. Allen (Member # 1351) on 12-13-2013, 09:00 PM:

Thanks for the tips guys. As I said I'm an operator not a tech. I'll try them out if I can't find a tech. Louis, is he the one who lives near Tulsa? Do you have a number for him?

Posted by Louis Bornwasser (Member # 3063) on 12-14-2013, 06:10 AM:

Yes. Broken Bow or something like that.

Posted by Steve Kraus (Member # 476) on 12-14-2013, 07:43 AM:

He's the one whose Motiograph mailbox heads up the FT photo section. I've been there. Saw a Century Showscan head.

Posted by Gordon McLeod (Member # 33) on 12-14-2013, 10:55 AM:

1 is it there in all formats
2 is it there if film sound (all formats)with the LED reader lit but no film
That will tend to start to isolate the problem of being in the processor or the reader

Posted by Mark Gulbrandsen (Member # 72) on 12-14-2013, 11:28 AM:

Just convert to digital. Problem solved!

Posted by Buck Wilson (Member # 5885) on 12-14-2013, 01:03 PM:

Let me know if you get a hold of that tech and if he is still doing work please!

Posted by Grant Chambers (Member # 7051) on 12-19-2013, 01:21 PM:

Chris Tyson, Sonic Equipment Company Sonic Equipment Company

Posted by Robert E. Allen (Member # 1351) on 12-19-2013, 07:48 PM:

I called Sonic and they sent a great 35mm tech named Johnathon down here.