Net stops working when connected to power supply

[reminder]

i have run into a strange problem.

Currently i am using a 56k modem for internet connection on my laptop. Everything has worked fine previously.

However, recently I could not connect to the net. I have realised that the problem is that if my laptop is connected to a power supply, the net connection stops. If I cut off the power supply, the net connection starts working.

Could this be to do with spyware?

Any idea how to solve this problem?

Thanks

[zaphodiv]

My guess, and this is just a guess, is that the modem is getting mains hum on the line. I just got a new dell laptop that is painfull to have in my lap when just wearing pants due to the leakage current from the unearthed power supply. I used to have an earth lead connected to the shell of a parallel port D connector for an old laptop, I'l have to make another.

Do you have a phone also connected to the line? Use hyperterminal to dial
another phone such a handy mobile while listening to the line. Do you
hear a buzz when the psu is connected?

I thik this is more of a problem in places like the UK with 230Volt electrics with the neutral usually connected to the earth at the local substation. I believe USA electrics typically have a center tap on the local pole transformer connected to earth. The upshot of this being that european live swings 230volts from earth but USA live is only 55volts
from earth. (In general 230volt electrics are vastly superior to 110volt but thats another story).

[lynx]

While I agree that some sort of mains interference can be a possibility, it should never be a problem on a laptop since the power supply should be providing smoothed DC current.

I suspect that the power supply may be failing and allowing an AC component into the supply lead. Protection circuits will be preventing this current from damaging the laptop (at least in the short term). Most circuits in the laptop will be stepped down from the raw supply and are therefore shielded from this effect. By comparison the modem requires a full 12V for its signalling and is therefore more likely to be affected.

A failure like this is also an obvious reason why you haven't experienced the problem before. If you can borrow a similar power supply (check the voltage and rating) you should be able to prove or disprove this without any cost. Otherwise you will have to get the power supply checked and may have to pay if it isn't faulty.

[zaphodiv]

it should never be a problem on a laptop since the power supply should be providing smoothed DC current.

The situation is more complex than that.
The laptop power is a DC voltage between the two wire on the psu output. The AC leakage is between the output wires and local earth.

The server just lost my longer reply and I have to go out now.