What's causing this interference with my projector?

Factual Questions
1

I just bought a new DLP projector, a Toshiba TDP-T45U, to replace my old one which is giving up the ghost.

When I’m watching TV or DVD movies on the projector, I sometimes get a horizontal line that scrolls slowly from the bottom to the top of the screen every 4-5 seconds. Sometimes this line takes the form of a small band of color (either very pale pink or green) that will scroll up and discolor the image as it passes through.

Here is the setup. I have a Comcast HD receiver and a DVD player which are connected to my Sony A/V receiver with component video cables (red/green/blue RCA cables). I have the same kind of cables going from the receiver to the projector with an adapter cable to connect to the projector’s VGA port. The projector is ceiling-mounted, with the cables running through the walls and coming out of the ceiling near the projector (total distance less than 25 feet).

With my old projector, I used the exact same setup (same cables, connectors, everything) and did not have this problem. Also, I am using the S-Video outputs of all the above components to go to my (non-HD) TV set when I don’t want to fire up the projector. I don’t see any of the interference lines on the TV.

My question is, have I got a defective projector that I need to return, or am I picking up interference somewhere in my video cables that I need to locate?

If any dopers have experienced this and figured out how to fix it, I would appreciate your input.

2

Can you pin down the “sometimes”?

From everything you’ve written it reads like the projector.

How’s the picture with another, similar, input?

3

I know something similar happens when you run a DVD output into a VCR input and then run that output to a TV (I had friends in college who had to use this setup. Their TV only had coax input, so they had to use the RCA input of the VCR and then output it through coax to the TV.)

I don’t think this would occur with just a video receiever, though, especially since you said the S-video outputs don’t have this problem. I’d make sure none of the cables are twisted around each other or near any electrical or telephone lines.

4

Do some research on “Ground loop” or “60 Hz hum.”
Your description sounds like it could be a ground loop. If the easy methods don’t work for you, good luck. I’ve been dealing with it for a few years now and for the life of me can’t pin it down.

5

Bingo! But why, “Ground Loop” or bad filter cap in projector?

6

Update: I reseated all the video cables, and it seems to have taken care of the problem. Maybe I didn’t have a solid ground connection on one of them or something.

Thanks, everyone for your input.