8mm Forum: GS 1200 Booming Sound: HELP! @ PAUL ADSETT

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Posted by Chip Gelmini (Member # 44) on May 05, 2018, 11:17 AM:

Booming Sound on GS 1200

This notice will best be read by those who own the GS 1200. On one machine, I have lost that “booming” sound, but first you must understand what I mean by this. Please use your projector the following way to help me with the diagnosis:

Use built in speakers. Do not connect to audio system otherwise.

Run a test reel that you know has fairly good sound on it with average VU meter movement.

Use a mono print.

Set the track 1 volume knob to about 1 & ½ using the numbered scale printed around the knob.

Observe how low your sound is at that point.

Next, turn the volume knob up to # 2 using the same printed scale and notice the booming sound.

The test is complete.

So my problem is based on the above:

At volume setting # 2 – it is as low as on your projector when set to 1 & ½.

On my projector turning it up to # 3 makes it booming.

This is more than just turning the sound up. I believe this is a problem with magnetic sound control.

The volume is much more normal with optical. Therefore, this is a problem with magnetic only.

What can I check for this. Do you recommend demagnetizing the head? The projector is a 3rd generation with black indicator lines on the volume knobs.

Thanks in advance for any information.

Chip Gelmini

Posted by Mike Spice (Member # 5957) on May 05, 2018, 02:26 PM:

de magnetizing the heads is a highly unlikely solution, cleaning the heads with ipa is always a good idea, but again, unlikely to be the cause of your problem

Posted by Paul Browning (Member # 2715) on May 06, 2018, 06:52 AM:

Chip you may have a flat spot on the carbon track of the volume control, perhaps the previous owner set it there when showing his movies, these are now over 30 years old, does the volume switch crackle or sound scratchy when turned?, if so you may be able to cure it with switch cleaner....

Posted by Maurice Leakey (Member # 916) on May 06, 2018, 01:45 PM:

You should first just turn the volume controls forwards and backwards many times. This will self lubricate the carbon track.

Posted by Chip Gelmini (Member # 44) on May 08, 2018, 09:13 AM:

Thanks support still required as nothing has worked so far.

Posted by Paul Adsett (Member # 25) on May 14, 2018, 07:59 PM:

Chip, something you might try if you have about an hour to spend:
On my GS'S I have found that the electrical contact interface between the amplifier module and the main chassis board often gives a problem because of corroded or poor contacts. Remove the amplifier cover and then remove the four bolts which bolt the amplifier to the chassis. Now gently pull off the amplifier module from the connector on the chassis. Then clean the electrical interface contacts on both the amplifier and the chassis with some contact cleaner. While your at it, blast the innards of the power supply with air to blow out any dust. Also try to get some contact solution down into the volume and tone control pots.
When you have done all this it may or may not solve your problem.

Posted by Jean-Pierre Labus (Member # 6090) on May 15, 2018, 09:58 AM:

You can read GS200 technical manual

http://www.film-tech.com/warehouse/manuals/GS1200SERVICE.pdf

Best regards

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