Grounding [buzz or hum] problem?

[mikehende]

Hey guys, how it going? Just back from a very short vacation and ready to pick up where I left off. The reason I created that "Basic Electricity" thread that some of you may know of, was to set the foundation for this problem I ran into a while back and no pc tech I talked to could come up with an answer.

I had bought a TV Tuner card to get the TV/Cable signal on my pc to record anything I wish and then burn to DVD. After connecting everything the only problem I ran into was/is there is a buzz or hum associated with the audio signal from the tv/cable and this noise is only present when coming into the pc so my TV/cable plays fine on it's own or even going through my Home Theatre System so there is nothing wrong on the tv or cable box end.

I was told that this is a "grounding" problem and should be taken care of "inside" the pc, called Dell but they couldn't help so I had to settle for using a Ground Loop Isolator which does the job effectively but I feel this only masks the problem, I want to not use the Isolator and fix the problem, especially later on if I should be fixing someone's pc that might have the same issue, I don't want to tell them I can't fix the problem.

So guys, this is a challenge, any ideas please? Thanks.

[PeteF]

So guys, this is a challenge, any ideas please? Thanks.

Yeah, first check the outlet using one of those 3 prong AC outlet
tester we talked about in the basic electronic thread.

Next, I'd look at the physical electric connections on the cable
TV line to ensure it's properly grounded.

---pete---

[mikehende]

Sorry, forgot to mention that I did all of the testing, exchanged power strips, cables and wall AC outlets and also pc's, the problem only occurs with this model [Dell Dimension 3000 and 2400], I don't get this problem when I connect my son's older Dell PIII pc so the problem is within the dell pcs which is why I am figuring that I have to do some sort of grounding "inside" the pc.

[PeteF]

Sorry, forgot to mention that I did all of the testing, exchanged power strips, cables and wall AC outlets and also pc's, the problem only occurs with this model [Dell Dimension 3000 and 2400], I don't get this problem when I connect my son's older Dell PIII pc so the problem is within the dell pcs which is why I am figuring that I have to do some sort of grounding "inside" the pc.

Start by using a different slot.

Make sure all the screws are installed on the motherboard.

After that, you could try grounding shield portion of the
cable input connector to chassis ground on the DELL.

After that, I'm not sure.

---pete---

[mikehende]

Start by using a different slot.

---pete---

Don't understand Pete? I am using the line-in on the integrated soundcard, the noise is there even when I use the mic input.

[kern]

Don't understand Pete? I am using the line-in on the integrated soundcard, the noise is there even when I use the mic input.

the "noise" could be coming from the pc's power supply.
integrated sound cards are susceptible to electrical interference aka "ripple" from the pc power supply, especially from "cheaper" power supplies.
the filter capacitors in the cheapies usually dont work properly, which allows AC power line noise to be mixed with the DC outputs, which affects adjacent chips.

[PeteF]

Don't understand Pete? I am using the line-in on the integrated soundcard, the noise is there even when I use the mic input.

Oh, ok, I misunderstood what the problem was.
In that case, go with Kern's suggestion and look into the PSU issue.
Substitution is probably the quickest way to determine if the PSU is bad.

---pete---

[mikehende]

ok guys, thanks!

[kelly]

I've seen this problem before and it had to do with the grounding of the electrical box and the grounding of the cable connection. At my house there is a difference in potential between the ground on the electrical outlet and the cable shield. This is because the electricity is grounded at one end of the house and the cable comes in at the other end.

To resolve the problem, I connected the cable to a 75 ohm coax to 300 ohm twin lead adapter. Then I reversed it using a 300 ohm twin lead to 75 ohm coax connector. This essentially isolates the grounds from each system. The hum went away.

-td