buzzing sound(machine gun sound) when turning on the computer? Faulty circuit what part?

I 've just received a free intel 815 motherboard with onboard sound.
The board is good except there is buzzing sound(sound like a machine
gun fires the bullets all the time) from the speaker jack(connect to
speaker). The sound starts at the POST and does not stop at all.

I swap the speaker, the power supply, reinstall all the compontents
and put the board on phone board. The problem still persists.

I have couples of sound cards, so putting a new card is not a problem.

I'm just curious of what part of the circuit is causing the problem?

On 7 Oct 2006 12:53:41 -0700, saturnlee@yahoo.com wrote:

>I 've just received a free intel 815 motherboard with onboard sound.
>The board is good except there is buzzing sound(sound like a machine
>gun fires the bullets all the time) from the speaker jack(connect to
>speaker). The sound starts at the POST and does not stop at all.
>
>I swap the speaker, the power supply, reinstall all the compontents
>and put the board on phone board. The problem still persists.
>
>I have couples of sound cards, so putting a new card is not a problem.
>
>I'm just curious of what part of the circuit is causing the problem?


The technical term is that you have a doohickey out of
whack.

Seriously, it's usually a lot of noise on the power rail
powering the audio DAC. Sometimes a different power supply
will help but other times it won't, or not enough as it's
also partially the particular components you have installed.
Often the larger consumers like a video card matter most
though you can't really blame the card per se, it might do
fine on another system and it's just the particular
combination causing noise the audio circuit is more
susceptible to.

I suppose it's possible a cable could be picking up some
noise too or instead, if you have a front audio panel
connected you might try disconnecting it.

Otherwise, use an audio card.

saturnlee@yahoo.com wrote:

> I 've just received a free intel 815 motherboard with onboard sound.
> The board is good except there is buzzing sound(sound like a machine
> gun fires the bullets all the time) from the speaker jack(connect to
> speaker). The sound starts at the POST and does not stop at all.
>
> I swap the speaker, the power supply, reinstall all the compontents
> and put the board on phone board. The problem still persists.
>
> I have couples of sound cards, so putting a new card is not a problem.
>
> I'm just curious of what part of the circuit is causing the problem?

Sounds like either clipped 50/100Hz, or else motorboating. A bad
capacitor could cause either, or a bad audio lead could cause it. It
might be worth unplugging the cd to soundcard lead just in case its the
lead or cd. Another sound card is probably the next easiest thing to
try. There is piggybacking decoupling caps, but its just easier not to
bother. Theres also the poss that the output jack has lost its ground
connection, you could try connecting your speaker ground to the metal
case. But a new sound card will cover most likely problems, and is
simple.


NT