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Author Topic: Hum/buzz when SH-1000 door is closed David E. Nedrow Master Film Handler Posts: 368 From: Columbus, OH, USA Registered: Oct 2008 posted 12-10-2011 08:07 PM                        We're still limping along with a seen-better-days USL JS 195, sans SR/A card.* Thankfully, virtually everything we show is DTS, so we usually don't run into any trouble. Every once in a while though, we get a film with no DTS option and have to run the analog track. In addition to the usual problems with the analog chain we experience, a new one popped up this time. We started MARGIN CALL Friday and during the first show, there was a pretty good low level sustained hum, along with a higher pitched buzz, that started as soon as the queue activated stereo. I had no idea what was going on. I checked everything and switched first to mono, then to bypass, which at least made it less disconcerting for the audience (hey, passes for everyone). After going to bypass, noting that the problem was still there, I opened the door of the SH-1000 to make sure everything looked correct. I verified that the film was latched over the sound head, etc. I had pushed on the latch to make sure it was tight, and checked the monitor for the noise. It was gone. Huh, something must have been loose. I then closed the door and, while walking past the monitor, realized that the hum was back. Hmm, could it be the door? Yes it could. With the door open, no hum. Door closed, hum. My thought is that something is at the outer limit of a tolerance, and the pressure of the door "stop" against the sound reader assembly is pushing it beyond and into audible land. It's a BACP RSTR-2000 reader and LED, but, at some point in the past, thick adhesive was packed around the locking screws that hold the reader. I'm not sure if I'll be able to do anything there. So, what should I look at first in re: adjustments? I'm pretty sure I have all the audio test films I need for analog. One other note. I've never been able to get the correct level out of this reader. It's output is well below Dolby ref. -David  |  IP: Logged Scott Norwood Film God Posts: 8146 From: Boston, MA. USA (1774.21 miles northeast of Dallas) Registered: Jun 99 posted 12-10-2011 08:17 PM                        My bet is that some light leakage from the port glass reflection or the shutter area of the projector is being reflected into the soundhead, which would cause a 48Hz hum (assuming a 2-bladed shutter). Usually, this happens when the door is open, not closed, however. As for the level, you may need to loosen the three screws the hold the LED part of the reader and rotate it slightly while running cat. 69T. There is some play there and you will see when the output peaks by looking at the meters on the processor. When you find the output peak, tighten the screws and re-set Dolby level. If this does not solve your problem, you can cut one or both of the links on the circuit board (which pulls straight out of the "lens" assembly of the reader) to increase the current to the LED (and reduce its life by a corresponding amount).  |  IP: Logged Martin McCaffery Film God Posts: 2481 From: Montgomery, AL Registered: Jun 99 posted 12-10-2011 08:17 PM                        Do you have a bright light near the soundhead? Stray light bouncing around the reader when the door opens is the first thing I'd check.  |  IP: Logged Darryl Spicer Film God Posts: 3250 From: Lexington, KY, USA Registered: Dec 2000 posted 12-10-2011 08:55 PM                    quote: David E. Nedrow I then closed the door and, while walking past the monitor, realized that the hum was back. Leave the door open.  |  IP: Logged David E. Nedrow Master Film Handler Posts: 368 From: Columbus, OH, USA Registered: Oct 2008 posted 12-11-2011 01:35 AM                        Gee, thanks Daryll. I knew there had to be someone who couldn't resist. "Doctor, Doctor, it hurts when I do this." "Well, don't do that. " In all seriousness though, I did check for reflections, etc. No port windows, no lights on in the booth. The 48Hz shutter hum sounds promising. I suppose the light could be reflecting off the inside of the sound head inspection window. I'll put some black paper tape on the inside of the window and check for hum (door closed).  |  IP: Logged Ian Parfrey Phenomenal Film Handler Posts: 1049 From: Imbil Australia 26 deg 27' 42.66" S 152 deg 42' 23.40" E Registered: Feb 2009 posted 12-11-2011 05:35 AM                     Easy stuff first. Is the hum 48 or 60hz? The answer to this will automatically eliminate one half of your (if applicable) stray light problem. 48Hz? - Then it has to be post shutter light bounce. 60Hz? - then it is either reflected flourescent light OR a possible LED power supply issue. The latter seems unlikely as you mentioned is goes when the door is opened. See if you can nail down the frequency and take it from there. Cheers  |  IP: Logged Kenneth Wuepper Phenomenal Film Handler Posts: 1026 From: Saginaw, MI, USA Registered: Feb 2002 posted 12-11-2011 06:45 AM                     Then there is also the possible pair of frequencies derived from the scanner centering. Too far in and you hear the DTS time code. (Like a vacuum cleaner in the lobby) or the sprocket holes (106 Hz). Since the closing of the door in this model sound head moves the tension roller closer to the sound drum, you could have a loose lateral guide setting and that will cause either of the noises mentioned depending on the scanning error. The adjusting and locking of this scanner is essentially a technician related adjustment requiring the use of test film and additional test equipment to have a properly done job. I would recommend also that you simply leave the door open until you can have a technician do a proper alignment of the scanner. KEN  |  IP: Logged Dave Macaulay Film God Posts: 2321 From: Toronto, Canada Registered: Apr 2001 posted 12-11-2011 10:01 AM                     I would remove the little rod that prevents the door from closing when the lay-on roller is not latched. That's the only mechanical thing that could do aything with the soundhead action, shifting the film so the DTS track, frame lines, or sprockets are picked up. If it still buzzes, you probably have an optical issue - light is getting into the reader. The BACP reader is pretty good at rejecting strange light sources but it can get interference. Fluorescent lights are a source of 120Hz buzz and light bouncing off the shutter is 48Hz. A 60Hz buzz is almost always a grounding issue. Make sure the soundhead case is properly grounded and that the optical reader output cables have the shields grounded at the processor end only.  |  IP: Logged Louis Bornwasser Film God Posts: 4441 From: prospect ky usa Registered: Mar 2005 posted 12-11-2011 11:10 AM                        I like Dave's rod idea. Especially true if door sags. Louis  |  IP: Logged Sam D. Chavez Film God Posts: 2153 From: Martinez, CA USA Registered: Aug 2003 posted 12-11-2011 12:08 PM                       I have not seen an "interlock" rod on the door of the Simplex soundhead in many years but it does sound like this door has one of these rods. It can be removed one way or another.  |  IP: Logged Tony Bandiera Jr Film God Posts: 3067 From: Moreland Idaho Registered: Apr 2004 posted 12-11-2011 11:46 PM                     Yep, Dave hit on the most likely culprit. BUT, as Scott and Ken hit upon, you MUST first get the reader and LED aligned properly before you go any further..and it is NOT a "do-it-yourself" project, you must have all the proper test loops and a 'scope AND an RTA to do it right..otherwise you're just pissin into the wind.  |  IP: Logged Kenneth Wuepper Phenomenal Film Handler Posts: 1026 From: Saginaw, MI, USA Registered: Feb 2002 posted 12-12-2011 08:18 AM                     Regarding the rod on the door of an SH-1000 sound reader: There is a possibility that an operator could leave the pad roller disengaged and start a reel without sound. The SH-1000 heads had that little fail safe by making it impossible to close the door when the pad roller was not properly engaged. I have seen the paint worn thin on the top of the doors of these units where the last act of threading was to run your hand across the top of the door to be sure the roller was engaged and the door was closed properly.  |  IP: Logged Robert Koch Film Handler Posts: 93 From: Williams Ca USA Registered: Apr 2006 posted 12-12-2011 01:31 PM                     The reason all those rods are missing is that the door would1`nt stay closed with the pressure roller latched at the end of the nite so to avoid flat spots on the felt roller you removed the damned rod.  |  IP: Logged Monte L Fullmer Film God Posts: 8367 From: Nampa, Idaho, USA Registered: Nov 2004 posted 12-13-2011 12:23 AM                     ..why at the end of the night, I leave all gates, traps and the door open - after I gave a good scrubdown in a booth that had the XL DeLuxe equipment..  |  IP: Logged Robert Koch Film Handler Posts: 93 From: Williams Ca USA Registered: Apr 2006 posted 12-13-2011 02:06 PM                     I tried to correct my post yesterday, but failed. Should have said door wouldnt stay closed with pressure roller UNLATCHED, and this was the reason to remove the rod.  |  IP: Logged

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