Strange problem with a new design-maybe a GND issue?

[udir]

Hi There
I am experiencing a weird problem with my newly design.
Its basically a simple carrier board with SOM that operates a touch screen and 2 other applications.
This device is Fed from simple 12 V DC power adaptor and is said to be "floating".
When I started testings and an external lab, they used a probe that generates a low voltage signal in a high frequency and touched either the power supply cable when its connected to the machine or the touch screen itself, and it suddenly froze! when i touch the screen nothing happens.....only restart helps.
I have no idea why it happens as the device is suppose to be floating.any idea how to attack this?
Ron

 

[jiripolivka]

With devices said to be "floating", then connecting another device referred to a ground often causes problems. I think a "floating" device allows to ground one of the DC lines, then the connection becomes safe. Make sure the positive and negative DC lines have a blocking capacitor(s) connected. The best is a parallel combination of a 100 uF and 0.1 uF capacitors . Usually the negative DC line is best to be GND.