Film-Tech Forum ARCHIVE: smart IIb processor hiss

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Posted by Charles Caron (Member # 3247) on 03-14-2008, 12:04 AM:

Greetings from the ubercrappy 7 [Wink]

... mod 2c, center & surround channels only. BACP red reader. center channel has loud white noise type hiss,surround channel very light hiss, no hiss on nonsync. Red reader blocked/powered down, noise lessens slightly. Processor off, no noise.
Second symptom/problem? touching red reader produces 60cy hum.
Bad ground to sound head? ground loop? If I missed in my search, please point me to the proper thread, Thanks, Charles

Posted by Demetris Thoupis (Member # 833) on 03-14-2008, 10:35 AM:

Check the BACP manual regarding a ground fix. If I remeber correctly you should link the (-) connection of the power supply input to the Ground of the Reader and then to your rack chassis ground. Do you have that hiss when you have the reader off? If you have a ground issue you should see the two green leds on the BACP reader slightly glowing when you have no film on the path and you have the reader ON. If you have the reader on and you don't see a slight glow on the Leds then most probably you are OK. Just a suggestion.
Demetris

Posted by Gordon McLeod (Member # 33) on 03-14-2008, 12:21 PM:

On smarts website in the tech tips used to be a fix for reverse scan and Jaxlight hum issues
Grouding sounds like an issue
Pull the preamp card and see if the hiss goes away
Also is the hiss there in mono as well as both stereo and sr
if it in all film formats I would suspect the preamp
otherwise the matrix card or the NR card

Posted by Charles Caron (Member # 3247) on 03-14-2008, 11:30 PM:

I swapped out all cards one at a time, swapped out power supply,
no luck. [Confused]

Noise occurs in all except music. Something on the backplane maybe?

Posted by Gordon McLeod (Member # 33) on 03-15-2008, 01:07 AM:

did it go away with the optical preamp removed ?
it could be calibration issues as well and it is clear there is a grounding issue from the comment about touching the reader

Posted by Mark Gulbrandsen (Member # 72) on 03-15-2008, 11:25 AM:

Charles,

First check the Smart modification for reverse scam readers. If its been done then....
Since some buildings have very strange grounding systems try grounding the terminal on the BACP that says (gnd) to the frame of the sound reproducer/projector. Normally this terminal is not connected in a normal install but on a couple of occasions with Smart processors sometimes it does the trick. Inversely if its connected you may want to disconnect it and see if things improve.

Also... like Gord says pull the solor cell preamp and then see if the sound goes away... likewise you can pull the module out of the BACP reader while the solor cell preamp is in place...

Posted by Charles Caron (Member # 3247) on 03-16-2008, 09:08 PM:

Mark: tried both of the above... still no joy [Confused]