Lines in display with thicker VGA cables... Pulling my hair out!!!

**bluepotpie** · 01-26-2009, 02:23 PM

I'm using Xenarc MDT-X7000 in dash motorized touchscreen display in my 2006 Mazda6. The PC is a PC-Chips (model P53 i think) and i'm using the onboard VGA output to go to the screen's VGA input. I've got 5 different VGA cables and 2 different VGA extension cables available for testing. All of the cables are very thick except for one, which is about as thick as a cat5 cable. Also, all of the cables work on other equipment (they were all in use and were pulled out to test the carPC).

My problem is this;

Using any configuration (except 1, which i'll get into later) of cabling (any combination of cables, routing, grounding, shielding, etc.), i get these horizontal lines in the screen that make it VERY hard to make out the picture. The lines are about 1 pixel thick and run all the way across the screen. They appear to be sections of the image that i should see, only shifted very far to the left. If need be, I can upload a picture of this later.

Now, as for the one configuration mentioned above...

The one thinner cable i have works! Picture is great. Only one problem, it's not long enough. It's about 3 feet too short. So to use it i have to have the computer moved to be closer to the cable. This is not an option for the permanent install. I was so excited when i saw that i found a cable that works but the excitement was short lived...

I figured, I just need to use an extension VGA cable now, right? Wrong. The extension cables i have are all very thick (which i thought would be better). When i use any thick cable in the mix of things, my mysterious lines come back!!!

ALSO..... I have an HP laptop (NC6000) that can somehow send a good clean signal to the screen no matter what cable i use. My buddy's Acer mini laptop can't though. We see the lines in the screen using his laptop.

Some of my own theories...

1. the thicker cables have larger wires which have larger electro-magnetic fields, which increase the possibility of crosstalk or noise.

2. Something is different in how the thicker cables are wired. (sharing signal grounds, etc.)

3. The gods are against me finishing this carPC in time to take it 16 hours west to show it off this weekend.

Please help me figure this out ASAP!!!

Thanks guys!

**2k1Toaster** · 01-26-2009, 02:54 PM

Well... you have pretty much deduced the problem, so good job with that

Thing is it is an odd problem. Thicker cables are better (usually). Do all your vga cables (the thin working one versus the non-thin one) have the same number of pins? VGA cables dont have to have all the pins in there connected either so one side may not have all pins. SOme are used for data back from the monitor like type/resolution that sort of thing.

My only guess right now is that the thicker ones probably have all pins exposed so the monitor is sending back data that it is not 800x600 but 800x480 and the graphics chip can't handle that weird resolution... But the thin cable doesnt send it out, so the computer doesnt know or care and just blasts it with 800x600 which the monitor then internally scales down to 800x480 by itself.

Other than that, I am pretty much stumped.

**bbalazs** · 01-26-2009, 06:19 PM

Ok, so you have to open the cable on one end OR make a small interface (male and female vga plug and wires as short as possible) and this tool will serve as an object of experiments.

First do what suggested by 2k1Toaster, unsolder the DDC wires (clk and data).
If it does not help try to disrupt the countinuity of the shielding firstly, in the case of nothing the ground wire(s) after.
Try to make the original (power) grounding of the monitor stronger (thicker wire directly to the metal part of the chassis).

A hard grounding by the way like that is VERY important even for the computer PS.

**bluepotpie** · 01-27-2009, 08:05 AM

Think i've figured something out here...

The smaller cable i have has all 15 pins on both ends whereas the larger ones have 1 pin missing, pin 10. Pin 10 is for "sync. ground" and would explain my issue. What i don't understand is why some other devices (different monitors, different computers, etc.) don't need this pin to work properly.

Any thoughts?

UPDATE:

I've scrounged up another thin VGA cable (with all 15 pins) from another LCD monitor and used a female/female coupler to make it work as an extension and all is good now. Still wondering about that pin issue though...