Laptop can't connect in AC power

[Ozvideo]

I tried to do some downloads from my wife's laptop the other day & was
surprised to find that I could not get a connection if the machine was
still operating from a transformer. If the transformer was connected I
could heard some noise coming from the modem. Unplug the transformed &
it all worked OK. I thought that the phone line which was immediately
next to the power cord was causing this interference but I was wrong
since moving the cord didn't help?

If you know another site which might be a better place to check please
advise.

 

[Ron Hardin]

I tried to do some downloads from my wife's laptop the other day & was
surprised to find that I could not get a connection if the machine was
still operating from a transformer. If the transformer was connected I
could heard some noise coming from the modem. Unplug the transformed &
it all worked OK. I thought that the phone line which was immediately
next to the power cord was causing this interference but I was wrong
since moving the cord didn't help?

If you know another site which might be a better place to check please
advise.

It sounds like a ground loop. The ground on your laptop and the ground on
your phone line are different, producing a current through the modem trying
to equalize the grounds, which shows up as noise. (The modem is a common
element in the power source and in the audio, so differences in the power
sources show up in the audio as well.)

You'd think the laptop would be isolated from the power ground but maybe it
isn't. I don't know how they wire the power transformers. Maybe they carry
the ground wire into the laptop.

You might check the wall outlet is wired correctly, as to reversal of neutral
and ground. There are cheap test things you can plug in that light if something's
wrong.