How do I clean my video signal?

TheDingo · 11-26-2000, 03:30 AM

Alright, after plenty of splicing and dicing, I was able to get the PC all plugged in running with success. The only problem is that I am getting some sort of feedback on the LCD. It is not major, but just some annoying white lines that slowly run down the screen. I have figured out that it isn't being caused by the inverter, so how do I clean the video signal?
Oh, and if it matters, my LCD is a 6.4" Clarion tapped off the ACC line going in to the stereo and was grounded straight to the car chasis. Would it possibly fix the problem if I tapped the LCD ground to the radio ground?

blkdragon6 · 11-26-2000, 05:25 AM

I'm having the exact same problem. At night it gets really annoying because then it's most noticable. I'm using a Prestige indash LCD and that slow moving white line is really getting to me. You're not alone my brother.

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Chris Snyder · 11-26-2000, 11:38 AM

Make sure that your video cable isn't running next to any power wires.

TheDingo · 11-26-2000, 11:46 PM

Hmmm, well, the cables for the video and power come from cable out of the screen... Other than that, the power isn't very close to the video.

schrodos · 11-27-2000, 02:07 AM

A lot of the time its not power because with DC power it runs very cleanly... a direct current as apposed to ac which you get all sorts of noise from. Usually the only time you get noise from DC is when it is turned on.

The LCD might be picking up interference if you have a radio by it or from your head unit? Have you tried moving it away from where ever it is to see if they went away?

Or maybe poor connectors.

Just suggestions...

Bj · 11-27-2000, 03:21 AM

I gather nobody reads my posts! I had the same problem, and it is caused by having a ground loop in your video. To fix it, disconnect the shield of the video cable at the LCD end. This prevents a ground loop occuring. It's exactly the same as an audio ground loop, except you can't see that. The "Hum" you hear on the audio is the exact same hum that appears on your LCD. You could use a video ground loop isolator (higher bandwidth than an audio type) or just try the shield cutting technique.

It worked for mine old crappy composite setup using an CVA 1000. I have RGB now, so it's no problem. (Pioneer AVX 7000). Upgrade to quality! You can actually read the text!

Anyway carry on....

TheDingo · 11-27-2000, 03:05 PM

BJ: Hmmm, I'm still a little confused about what meant by taking off the shield on the video cable. Do you mean the whole plug? Or just that round metal plate around the center pin?

DodgeCummins · 11-27-2000, 03:16 PM

Once again I have not had that problem. and actually I ran crappy cables for the video.

All my power supplies originate from the same 12v power and ground.

Just like Bj preaches fixing your ground loops. I preach troubleshoot throughly and isolate the problem.

See if you can run a different video source through the same wires with the computer running (like a VCR)

It is a known fact that if you have cables running along side each other that it is possibly to transfer interference that way.

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blkdragon6 · 11-27-2000, 06:07 PM

I also have the same problem when I bring the computer into the house and run it into my vcr. I use a different cable when I plug it into the vcr and the cables are definitely seperated from each other.

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DodgeCummins · 11-28-2000, 08:43 AM

I am taking a stab, but it sounds like a refresh rate frequency problem. I have seen it on some laptops outputting to a VGA LCD screen (small). Basically the screen wants 60 hz but it is getting something different.

In your case, the screen may be set up for a different rate (I couldn't imagine why)

blkgragon- I assume your screen does this even when hooked up to a standard video source like the VCR?

My 4" LCD came pre wired for the RCA video input. Perhaps yours was miswired or improperly soldered.

My LCD right now is sitting next to the desktop and my monitor (touching both actually) I get no interference so I wouldn't think it is the rfi causing it.

The other choice could be power supply...but again I haven't noticed any problem on mine with car voltage, big 2 amp power supply, or an undersized 300ma power supply (it smelt like it was going to burn up)

I say check all the connections and keep troubleshooting,
Good Luck!

TheDingo · 11-29-2000, 02:36 PM

Dodge: I guess the refresh could be a possibility, but it seems like a modern video card with a TV out would adjust the refresh for the output on its own. Anyone know what the refresh of a regular TV is? Worth a try.

blkdragon6 · 11-29-2000, 05:53 PM

US is 60 Hertz. With this in mind, my video card says it's giving out 60 Hertz. Is the refresh rate on an LCD with video input the same as a TV? If this is the case, then the refresh rate theory isn't what's wrong with my system.

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TheDingo · 11-29-2000, 08:44 PM

Yeah, actually can't be the problem. While I'm sure that an LCD screen made with a video input runs at 60hz, I just remembered that I had this system up and running in my home (including the LCD) and it didn't have that problem, so it must be ground noice from the power...

blkdragon6 · 11-30-2000, 12:12 AM

anyone know where to get a video ground loop isolator? Would be nice to try that baby out.

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DodgeCummins · 11-30-2000, 08:10 AM

The reason I threw out the refresh rate thing is because we bought a set of 8" Analogue VGA displays (not NTSC) and were testing them on a Dell laptop.

The displays show the same line or lines scrolling down the screen.

The same displays hooked up to Panasonic Toughbooks did not show the lines.

Both machines were set to 60hz, but the Dell was just far enough off to cause that problem.

Dingo,
Like you said, if it works fine off a regular Video source, then the screen isn't the problem.

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