Universal charger causes VGA noise, where to ground?

**swift_gti** · 01-02-2007, 08:06 PM

Hi all,
after finally getting my lilliput back from repair i'm hoping to finish my car pc, but my last problem is noise on the screen when my charger is plugged into the laptop..

Here is the scene:
----------------------------------------
Car ISO connectors to speakers + power

^
|

Lilliput 701NP/C indash

^ ^ ^
| USB | VGA | 2x RCA + GND loop isolator
| | | 3.5mm Stereo Jack

Toshiba Laptop

^
| Universal Laptop charger

Car Cigarette lighter socket
-------------------------------------

Now everything works perfectly when running the laptop from batteries, but as soon as I plug the charger in I got ground loop noise, so I tested the charger when it was wired to the same power and gnd as the lilliput screen - not much difference in ground loop noise (maybe SLIGHTLY better)
So I got myself a ground loop isolator and now the noise is gone, but its now finding a route through the VGA lead to the screen causing horizontal lines..

I have quickly tested grounding the metal plate where the VGA, USB, Serial etc.. is on the back of the laptop to a point on my chassis and the picture does improve but there are still lines visible...
I am going to test with the charger back on the same power as the lilliput tomorrow and maybe ground the back plate of the laptop to the same point.

Is there anything else I can try? I was wondering if I should be grounding anything else to the car ?

Thanks for any suggestions!

**carabuser** · 01-02-2007, 08:23 PM

How's your Lilliput powered again? I didn't quite get it from the diagram.

I had a similar problem, but mine was powered by an inverter, running from the cigarette lighter. My way out was to ground the charger of the Lilliput. My laptop charger/power supply is grounded to the chassis as well (different point though). Make sure you know which part of the plug is negative and try to ground it.

**swift_gti** · 01-02-2007, 09:19 PM

hehe, sorry about the poor diagram!

my lilliput is the indash model so it connects directly to the cars stereo wiring loom, which is where i plan to test grounding the charger to tomorrow..