Weird video interference problem! HELP!

lookinco · 10-08-2004, 11:11 AM

Right now my computer is connected through my headunit. The headunit is a Pioneer with a 7" indash LCD. Right now on the screen there is interference with horizontal bars scrolling up and down. As I step on the gas and engine rev up, the interference's frequency will change. So it's very similar to an alternator whine but now it's video instead of audio.

I tried to unplug the RCA going into the headunit -> no interference and no change with engine rev

I tried to plug back the RCA into the headunit -> interterence that changes along with engine rev

The interference is there ONLY when the engine is turned on. Everything including headunit, computer, other screens are wired from 12v straight from battery and to the same ground in the trunk. All other screens do not have any kind of interference whether the engine is on or off. The only screen that has interference is the one with the Pioneer headunit.

One thing I noticed was that when I grounded the shield of the RCA cable, the interference decreased.

So what exactly is the problem and how could I fix it? Do I have a ground loop between the video source and my headunit? If yes, how could I eliminate it. Would buying one of those Video Ground Loop Isolator fix the problem?

canadamatt · 05-01-2007, 04:46 PM

sorry i have no answers or anythin but i thought i'd empathize.

i have a inovatek in car LCD screen head unit. with the engine off, everything plays great including the screen but when i turn on my engine a very annoying noise is produced out of the rear speaker which are amplified. this sound's frequency is directly proportional to the revolutions of my engine.

i am hoping that if someone can answer your question, the solution may be helpful for my situation.

thank you

chaotic · 05-08-2007, 07:41 AM

Quote: Originally Posted by canadamatt

sorry i have no answers or anythin but i thought i'd empathize.

i have a inovatek in car LCD screen head unit. with the engine off, everything plays great including the screen but when i turn on my engine a very annoying noise is produced out of the rear speaker which are amplified. this sound's frequency is directly proportional to the revolutions of my engine.

i am hoping that if someone can answer your question, the solution may be helpful for my situation.

thank you

your issue is simple to fix, same issue i had. Go to circuit city and get a ground loop isolater cost me $17. Do you use some sort of audio connection like RCA or stereo headphone connection. If its RCA this makes your life very easy it has RED/WHITE in and RED/WHITE out. Took me 5 seconds to completely remove interference. I'm still trying to find out the solution to my video distortion now

Good luck

SubieRX · 05-15-2007, 02:10 AM

Hey guys! This is my first post. I've been lurking for a bit, and its a great site!

Here's my problem:

I'm having the same horizontal lines running up and down the screen. When I rev or give it gas, the frequency changes and the lines speed up as well.

But for my screen, it makes no difference what its connected to. I can have the RCA's unplugged, and the only wires running into it are the 12V+ from the battery, and the ground wire (all grounds are ground to a single point on the chassis). The power wires are far away from the RCA's, and moving the power cord around doesn't affect the interference. I've installed a cheap DC noise filter I got off ebay, and it didn't do anything at all. It looks exactly the same as before I wired it in.

Also, when the engine is off, the screen is crystal clear. No lines at all.

Anyone have any insight on this? I'm pretty sure its not a ground loop issue, as I all the grounds go to one point. And if its alternator whine or something similar to that, wouldn't the DC noise filter clean it up? This is driving me insane.

Edit: I'm not running a CarPC, at least not yet. I just have a pyle LCD screen custom fit into my dash. I have a JVC headunit that runs an RCA into the LCD.

SubieRX · 05-16-2007, 06:30 PM

Bump anyone?

05-16-2007, 06:57 PM

You're getting some sort of EMI that's affecting your display. How's the shielding and grounding?

SubieRX · 05-18-2007, 04:36 AM

Thats what I thought it was at first... I have everything grounded to a single point on the chassis with 12ga wire. I've also pulled the screen out of the dash while everything is still hooked up and checked to see if the frequency changes or not when I move it around. At least to me, the frequency of the noice remained exactly the same whether the screen was placed in its original spot, or moved around further away from all the other electronics. I could be dead wrong since I'm new to all of this, but if it was EMI, wouldn't the frequency change when I moved the screen around?

I was thinking about building a makeshift faraday cage to test whether or not its EMI, but I haven't gotten around to it just yet. Any suggestions guys?

uhohrobbo · 05-18-2007, 06:02 AM

How long is the VGA or RCA cable to your monitor? I did try using 10M VGA cable with my lilliput screen and the picture quality was rubbish. When I replaced it with a 3M cable it was fine.

Try using a shorter cable (just to see if it gets any better). If the short cable works I guess you might need to buy / make some kind of intervference filter. Maybe even change the signals to RS-422 but I guess that would be a last resort.

05-18-2007, 11:15 AM

I almost forgot, does the VGA cable have ferrite cores on each end? Shorter cable definitely helps. I wonder why these screends don't have DVI :-(

Thelgord · 05-18-2007, 11:27 AM

Not EMI, but alternator noise. This has been an issue as far back as CB Radio's in the late 60's. Try an inline voltage regulator/noise suppresor. You can find them fairly cheap at radio shack. Also, try using more than one grounding point, or changing or cleaning your ground point.

SubieRX · 05-18-2007, 02:16 PM

Thelgord, I have a DC noise filter that have wired in right now, and it didn't make a difference. Is a filter different than an in-line voltage regulator?

Thanks for the help guys, the RCA is already a 3m though. That was one of the first things I tried and the noise is still there. Man, this is driving me nuts.

Sal R. · 05-18-2007, 03:15 PM

I'm having the same problems, though I think mine is a shielding problem.

It's not as bad as it was before, but two things did help:

Moving the VGA line away from any other power/signal lines and changing my ground.

Hope that helps. I'm still getting a faint interference, but it's not longer engine driven and is less noticeable. It's still there tho.

Hindmost · 05-20-2007, 03:50 PM

You may try shielding your cables somehow or shielding the back of your display. Try covering the back of your display with tinfoil as a test to see whether it makes any difference. Some will laugh but this is an excellent way to help identify just what the interference is affecting.

uhohrobbo · 05-21-2007, 10:28 AM

Yeh I was going to suggest wrapping tin foil around the cable. But there is no pint in doing either unless you ground the tin foil!

Have you tried using a VGA cable? Or a different RCA?

tracker64 · 05-21-2007, 10:45 AM

OK, change your video cable, heres why

check video extension cable i tried had same issue, i had a 25 foot SHIELDED cable laying around, decided, what the hell ill give it a try, and no video distortion. I use THX cabling for audio as well from trunk to front headunit, everything sounds and looks great

hope this helps you!

Tony