8mm Forum: Diagnosing sound problems in projectors

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Posted by Paul Brandes (Member # 2046) on November 05, 2011, 09:31 PM:

I would be interested if any of the knowledgable people on this site could offer any suggestions about where to start diagnosing a projector that wont play sound. I have a Bell and Howell,DCR Filmosonic sound projector that has no sound output. I have put a sound film through it, picture is fine but no sound. I just wanted to get an idea of where to start as I have no real technical knowledge about this. Also, I havent been able to find a technician who caters to this type of repair. I would be grateful for any help.
Thank you

Regards

Paul

Posted by William Mouroukas (Member # 2764) on November 05, 2011, 09:43 PM:

I take that you've checked the basics such as speaker connections, cleaned the audio head, turned the volume Nob several times to clean the pot contacts.
You could contact Frank who I understand services some makes and is based in Queensland:
dogtor@projectorheaven.com.au

Posted by Paul Brandes (Member # 2046) on November 05, 2011, 10:38 PM:

Thanks William,
Yes I have checked all those things.I was hoping to find someone closer to me in the event that something can be done to fix the problem.

Posted by Steve Klare (Member # 12) on November 05, 2011, 11:23 PM:

A good clue what's going on is what you hear when you mess around with the volume control. If you turn the volume up and hear low frequency hum from the speaker that means at least you have power going into the sound circuit and a signal coming out to the speaker. Real dead silence means somewhere something is disconnected or some circuit element has failed.

Something to try if you have some sort of external speaker or headphone jack is to plug into those and see if sound is coming through that route. If it does then you have a dividing line of where the problem is and where it's not.

Posted by Paul Brandes (Member # 2046) on November 05, 2011, 11:56 PM:

Hi Steve,

Thanks for your advice. There is some hum when I turn up the volume and there is an external jack for a headphone. I dont think I have the right size plug as the only headphones I have are too small to lug in so ill need an adapter.

Regards

Paul

Posted by Steve Klare (Member # 12) on November 06, 2011, 05:56 AM:

OK, That's a beginning...

I don't actually know this machine,so I'll have to guess based on ones I do know.

One thing that I've seen cause a loss of sound is the film not being pressed down on the playback head. The Elmos (As an example) have a mechanism that opens up the passage past the heads for every setting except forward projection but clamps down on the film when it's time for sound. I've seen this get hung up so the film is not touching the head and there is just hum.

Is there any mechanism moving above the heads on your machine when you change from "thread" to "project"?

A test for your head is to move a piece of metal close to the head(something small like a ring will do) and see if the hum changes. This can't work if the head is enclosed and shielded like a Eumig 800 series.

Posted by Paul Brandes (Member # 2046) on November 06, 2011, 01:48 PM:

I can't see any mechanism moving above the heads when I switch from thread to project. All I can see is the bottom section of the sound head move up and press against the top section when I turn the main switch from project to "sound". The rubber wheel is also brought into contact with the the flywheel shaft at this time.

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