Film-Tech Forum ARCHIVE: CP55 Hum

my profile | my password | search | faq & rules | forum home

»	Film-Tech Forum ARCHIVE » Operations » Film Handlers' Forum » CP55 Hum

Author

Topic: CP55 Hum

Richard May
Phenomenal Film Handler

Posts: 1057
From: Floral Park, NY USA
Registered: Aug 2004

posted 02-26-2008 07:23 PM

I couldn't seem to find the answer with the search so here goes. I have a bad buzz in L,C,R,and Surrounds. All formats including non sync. I pulled all the inputs out of the amps and it goes away. Sounds like the processor. Problem is, the fader does not control the hum. Stays same level no matter what setting. Mute too. In bypass it stays the same also. Tried ground wires here and there. Diconnected the monitor leads. Turned off Reverse scan. Nothing. Also noticed that the Cat 249 regulator card is very hot. Any other ideas?

| IP: Logged

Adam Holland
Film Handler

Posts: 66
From: Oak Grove, LA
Registered: Nov 2007

posted 02-26-2008 08:07 PM

I don't know what type of system you have but have you tried jumping your ground. I have had a problem that sounds similar to what you have at several athletic stadiums I have worked at as a public address announcer, both Division I-A and High School. It happens when I plug my computer in then tie it to the sound system via an 1/8 to RCA cable.

When I take a simple three prong to two prong adapter that you can buy at your local hardware store and plug the amp into it then into the wall the hum goes away.

I also had the same problem at the FISKE with our current set up showing a movie. I did the same thing but this time used the adapter to plug the computer in and it worked as well.

Due to waiting to get a state grant for new 35mm equipment we are using a computer and an LCD projector at this time in our project.

| IP: Logged

Ken Lackner
Phenomenal Film Handler

Posts: 1907
From: Atlanta, GA, USA
Registered: Sep 2001

posted 02-26-2008 08:29 PM

I have run across auditoriums that have had hums similar to what you describe. I tried the same troubleshooting steps with very similar results. I finally figured out what the problem was. The processor outputs were not wired correctly. Instead of individually sheilded pairs, all channels were wired with a single multi-conductor cable. What's even worse (and I could not believe this) was the negatives were not even connected. Removing these cables and running individually sheilded pairs for each channel corrected the hum.

| IP: Logged

Richard May
Phenomenal Film Handler

Posts: 1057
From: Floral Park, NY USA
Registered: Aug 2004

posted 02-27-2008 07:12 AM

All the processor inputs are individual cables. I did not try lifting the ground. I will do that next. I am wondering if there is a power supply issue. I thought I remember reading somewhere about power supply issues with the 55.

| IP: Logged

John Walsh
Film God

Posts: 2490
From: Connecticut, USA, Earth, Milky Way
Registered: Oct 1999

posted 02-27-2008 08:19 AM

My first guess would be the power supply. I assuming this is a problem that just started happening, rather than a new or recent installation?

| IP: Logged

Richard May
Phenomenal Film Handler

Posts: 1057
From: Floral Park, NY USA
Registered: Aug 2004

posted 02-27-2008 08:40 AM

Hi John. This unit has been running at this theater for over 20 years now. I was thinking the power supply. I found it strange that the hum didn't change with the fader or mute.

| IP: Logged

Steve Guttag
We forgot the crackers Gromit!!!

Posts: 12814
From: Annapolis, MD
Registered: Dec 1999

posted 02-27-2008 09:50 AM

Power supply, possibly, I would look to the Cat 249 regulator board first. It was not the best thing in the world and was replaced by the Cat 249A in the CP-65. I've had many Cat 249s go bad (and almost all overheat...pull it out and I'll wager you have a large blackened area on the board). The cat 249A also uses larger filter caps.

Steve

| IP: Logged

Richard May
Phenomenal Film Handler

Posts: 1057
From: Floral Park, NY USA
Registered: Aug 2004

posted 03-06-2008 01:52 PM

Very weird. Found an old 1/4" chassis mount female plug attached to front of console. It was used for the old FM style hearing impaired unit. It was hooked up to center channel out on processor. Disconnected it and entire hum went away. Thanks for all your replies.

| IP: Logged

Frank Angel
Film God

Posts: 5305
From: Brooklyn NY USA
Registered: Dec 1999

posted 03-10-2008 09:05 AM

quote:
I have a bad buzz in L,C,R,and Surrounds.....Disconnected it and entire hum went away.

Very different sounds, usually with different possible causes. Which was it, actually?

| IP: Logged

Richard May
Phenomenal Film Handler

Posts: 1057
From: Floral Park, NY USA
Registered: Aug 2004

posted 03-11-2008 10:57 AM

Buzz like a bee...lol. Sorry Frank. You're right. Two toatally different things.

| IP: Logged

All times are Central (GMT -6:00)

Printer-friendly view of this topic

The Film-Tech Forums are designed for various members related to the cinema industry to express their opinions, viewpoints and testimonials on various products, services and events based upon speculation, personal knowledge and factual information through use, therefore all views represented here allow no liability upon the publishers of this web site and the owners of said views assume no liability for any ill will resulting from these postings. The posts made here are for educational as well as entertainment purposes and as such anyone viewing this portion of the website must accept these views as statements of the author of that opinion and agrees to release the authors from any and all liability.