Intermitent induced noise in my vga signal?

Farrow099 · 12-23-2006, 11:06 PM

I am having trouble with noise in my VGA signal to my monitor... Its very bizzarre because sometimes its perfectly clear, other times its ALL wavy.

I went as far as to wrap my power cable, vga cable, and its switching power supply in EMF reducing tape!

In any event, I noticed while sitting in my driveway, that when I hold the brake it vastly reduces the static being induced into the signal?! So i'm thinking perhaps there is a wiring issue with the brake lights?

Any thoughts would be appreciated, I'm all out of ideas!

TM-868 ebay monitor (i'd try a different one if it wasn't already integrated into my dash!), vga extension with dual ferrite cores.

Motorcity · 12-24-2006, 12:59 AM

sounds like you have a ground issue.

Farrow099 · 12-24-2006, 02:07 AM

Yeah, I've tried different grounds though... There is however a factory equipment ground for something next to my passenger seat which I am going to try extending to the same location everything else is grounded.

Motorcity · 12-24-2006, 10:11 AM

the shortere your ground wires, the better. If possible, ground your monitor and computer directly to the chassis. Also, I suggest that you do not tie into the ground wire of another accessory. Give the monitor and computer their own ground points.

Farrow099 · 12-24-2006, 06:36 PM

*UPDATE*

I wrapped the power and vga in the tape, no effect...

On the upside I found an ebay seller that sells split bead ferrite cores, so I ordered 2 of those for $7.50 and i have much more confidence that that will clear it up

jason12 · 12-24-2006, 07:58 PM

Don't think ferrite beads will work. They are designed for very high frequencies.

The ground noise is observed when return current of one device (alternator for instance) chooses the path of ground connection between carputer and monitor. To minimize the grounding issues monitor and carputer have to be connected to the car chassis at one point.

This is why powering of the monitor from the carputer's power supply is so successfull.

Farrow099 · 12-24-2006, 09:40 PM

I tried powering and grounding the monitor's dc-dc regulator from the same distro blocks as the laptop (and everything else) but it didn't make any difference.

I'm considering running my ground distro block straight back to the battery and grounding EVERYTHING to it for good measure... But I'm fairly certain this particular problem is not due to grounding. (I've tried several locations)

The vga out of the monitor doesn't have any filters, only the extension from the trunk does - which is only half the distance.

But I could certainly be wrong

TruckinMP3 · 12-24-2006, 09:47 PM

How are you getting 12v positive and ground to the monitor?

Farrow099 · 12-24-2006, 10:35 PM

I had it (for 6 months) coming directly from the distro blocks that everything else is hooked up to... But I recently rewired both positive and ground (in an effort to reduce noise) directly to the fuse box. Moving it had no effect.

*NOTE* I have very little noise in my audio - inaudible with the engine running. And my monitor only gets "wavy" with the engine running.

TruckinMP3 · 12-25-2006, 09:54 AM

If your Power Supply can handle the load of the monitor, I would suggest getting 12 volts from that. The power will be cleaner than the fuse box or the battery directly. It may fix the noise.

Farrow099 · 12-27-2006, 04:14 AM

Its a laptop

As an update, I decided to dispell the possibility of grounding issues and ran the ground for everything all the way back to the battery... Only took 3hrs start to finish, haha. No difference.

jason12 · 12-27-2006, 12:45 PM

I wonder if it's the monitor's fluorescent lamp circuitry introduces the noice. The fact that holding a brake lowers the noice kind of explains it. Brake is on - voltage at the monitor gets lower - lamp inverter operating frequency shifts - lower noise.

On my monitor (DWW-720) some wavy noise is slightly noticeble sometimes on dark objects. I think it is lamp inverter frequency beating against refresh rate of the monitor.

Farrow099 · 12-27-2006, 01:41 PM

Its funny you mention that; I had previously installed a voltage booster on my alternator (basically a diode that tells the regulator to increase voltage another half volt).

THAT caused my monitor (or regulator) to make noise in my audio system. Removing the booster dropped my voltage to 13.8v plus or minus and completely got rid of the noise in the audio system. I did alot of testing to find that it was the coming from the monitor btw. Switching the voltage on the regulator changed the pitch of the noise, car on/off changed the pitch with each voltage setting on the regulator, and ofcourse then running the car at 13.8 got rid of the noise.

The monitor/regulator seem to tolerate any voltage between 11.5 and 14 volts while on the 12v regulated setting. Anything more makes a high pitched noise, anything less makes a low pitched noise.