Earth hum 3

[whiffy]

Hi,

Please forgive me but I know very little about electrics.
My problem is that I have a laptop that creates a static like humm/hiss with added squelchy noises when the mouse is moved or when the built in LCD screen refreshes.
I don't get this noise when it uses it's battery (which lasts for about an hour if I'm lucky).
I was hoping to use it for music production but it won't be much use for that in this state.
Now then, is it likely to be a laptop problem or a power supply problem?
How can I tell and what can I do about it?

Thanks.

 

[micman]

Make sure you use the its own power supply transformer.

The fact that the noise is produced ONLY when you plug it on the AC power supply indicates

1. The power supply transformer has a selector of AC input voltage (110V / 220V) and its turned onto the wrong power rating (110V in US, 220V in Europe).

2. The transformer is not the original one or it's mulfunctioning thus giving your PC a voltage lower or higher than the one that it's supposed to give.

Ask for support at the store tht you bought the PC. Tell them to use an oscilloscope to see whether the transformer actually produces the correct voltage rating needed by your PC. If not you should either have replaced or repaired before you do some REAL damage to your PC.

NOTE: It could also be a problem of the electric company but that's highly unlike.

Hope that helped. Michael Manos
Automation R&D

 

[Reyn]

I would have to say that micman is pretty much on the right path here. My bet would be that a filter capacitor in the power supply is going bad and will only get worse which means the hum will only get worse...replace it and things should be fine.

 

[Najemikon]

If the line in or mic in audio channels are enabled, you may find these are picking up a little interference from the AC. This can definitely cause you to 'hear' the mouse.

I get this on my PC & I've heard it on laptops before. Easy to test- plug in your power supply, listen to the hum & then open up your audio mixer & mute the mic & line in. If the hum stays (or if they were already muted), unplug it & run away!

Seriously, if this is the case, I don't know if it's an accepted 'feature' or if I should have been investigating it before. I just mess around with the volumes of the two in channels to get rid of it; they do have to be high to cause it & for most audio applications it would be too high anyway. May be a consideration if you're planning to use these analogue ports to any extent though for your music. Most of my applications come from other sources so I never need to use those two.

 

[mistanapesis]

I have had the same problem only with a TV card which used the line in socket on the sound card for input for sound. Never happened unless the line in socket was plugged in (sound blaster live)Then the mouse movement produced the sound of the mouse moving. I was told to enable the Spread Spectrum in the BIOS. It almost cut out 70% of it. Must be something to do with interference. If your unsure....Dont do it!

 

[whiffy]

Thanks everyone for your help.
I shall try the power supply solution. The dodgy capacitor theory sounds likely as the laptop has not always made this noise.
Thanks again.