Audio Noise from Shields

[flyvans.com]

Hi,

i'm still troubleshooting some noise in the audio system coming from a lcd-backlight inverter.
tried many many things and to make a long story short, when i "ungrounded" the shields, all noise was gone and everything seems to work just fine!!!
anyone have a clue where to look further?
is it a problem to let the shields "float"?
what i haven't had time to check any more today is wheter the shields remain grounded through an alternate path, which of course could explain part of the mystery. i highly doubt that would be the case though.
funny that the shields which should prevent problems actually cause some...

thanks for experience/tips/advice.

rgds,
bernie

[apkp777]

If un-grounding the shields worked then great. No problem. However, it's possible that your inverter (nasty noise makes) ground is energizing the airframe and to your shield?. Big noise makers are tough to isolate. You may try installing a Condensor in the path to ground from the inverter. I have been out of the R&E loop for a lot of years so, there are some that probably have better solutions.

[longranger]

Lacking specific direction from installation manuals, a good rule of thumb is to only ground shields on one end (usually the source end), and float the other. The idea is to preclude the shield from carrying current, due to slightly differing potentials at different points in the airframe.

[flyvans.com]

yeah we observed the single end grounding of the shields rule.
as a matter of fact wiring is just about per the gma-340 install manual.
will debug further but might as well leave the shields float in the air.
need some more time.

rgds,
bernie