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From: Jerohm on 21 Jan 2008 17:51
When I connect my television to the laptop using a S-Video cable, I get a
loud hum in the TV's audio (even with no audio cable connected) WHEN the
laptop is ALSO connected to the AC adapter - the video is fine with no
interference. The hum exists even if the computer is shut off (no video of
course in THIS case!), but still connected to the AC adapter. The hum is
pretty much non-existent when running off the battery. I tried a couple of
different cables with the same results. I ALSO have an old Sony VAIO that I
use in the same configuration, with no problems whatsoever. Any ideas?

Thanks


From: Art on 22 Jan 2008 06:24
Unsure whether you are trying to use your TV as a computer monitor or
as a TV display. S-video is strictly a video feed. Do you get the hum
when the AC adapter is plugged in, not connected to the laptop, and the
laptop is turned off? If so, the interference would be coming strictly
from the AC adapter. If not, there may be some interaction between the
laptop & the adapter, or a component in the laptop's power handling
circuitry is at fault.
Make sure your TV and your AC adapter are plugged into the same outlet,
or at least the same AC circuit in your house. Variations in ground
potential can produce or aggravate hum.
Most AC adapters for laptops have a lump on them, looks like a small
plastic cylinder clipped over the cable. There's some magnetic material
inside that is supposed to diminish extraneous frequencies & prevent the
type of problem you note. If this is missing or defective, the adapter may
produce or transmit interference. If you have another compatible AC
adapter, try that. If not, try putting about 6 loops in the end of the
adapter cable, & tape them into a bundle. This is a quick & dirty way of
diminishing interference for some frequencies & might decrease the problem.
If not, your experiment won't take long to undo.
There are also components in AC adapters (usually capacitors) that can
go bad & produce just this kind of interference. There are things you can
do to audio cables to filter out hum, but are beyond the scope of what I
know.


"Jerohm" <jDrEmLoEhTrE(a)snet.net> wrote in message
news:%l9lj.54$5K1.52(a)newssvr12.news.prodigy.net...
> When I connect my television to the laptop using a S-Video cable, I get a
> loud hum in the TV's audio (even with no audio cable connected) WHEN the
> laptop is ALSO connected to the AC adapter - the video is fine with no
> interference.


From: Jerohm on 22 Jan 2008 08:33

"Art" <artfd(a)hotmail.com> wrote in message
news:Lnklj.2234$Rg1.1183(a)nlpi068.nbdc.sbc.com...
> Unsure whether you are trying to use your TV as a computer monitor or
> as a TV display. S-video is strictly a video feed.

I am a aware that the S-video is strictly for video, but it injects a hum
into the audio side
no matter what device I plug the S-video cable into. Besides the TV, I have
the same problem
if I plug it into a Home Theater preamp with video switching capabilities.
I was attempting to use
the TV display for watching DVDs ...

The TV has ANT-A, ANT-B, AUX-1, AUX-2, AUX-3 inputs.
If the Power Supply (live!), computer (ON or OFF) and S-Video cable are
plugged in to
ANY of the AUX inputs... it interjects hum in the audio NO MATTER which
input is currently
selected.

> Do you get the hum when the AC adapter is plugged in, not connected to the
> laptop, and the laptop is turned off?

Nope, only when the AC adapter is plugged into the computer and the S-Video
cable is connected
to the TV. It doesn't even matter if the computer is turned on or NOT!

> If so, the interference would be coming strictly from the AC adapter. If
> not, there may be some interaction between the laptop & the adapter, or a
> component in the laptop's power handling circuitry is at fault.

> Make sure your TV and your AC adapter are plugged into the same outlet,
> or at least the same AC circuit in your house. Variations in ground
> potential can produce or aggravate hum.

Good suggestion, but I DID try that too ... no difference.

> Most AC adapters for laptops have a lump on them, looks like a small
> plastic cylinder clipped over the cable. There's some magnetic material
> inside that is supposed to diminish extraneous frequencies & prevent the
> type of problem you note. If this is missing or defective, the adapter
> may produce or transmit interference.

No lumps (chokes?) on this particular supply

> If you have another compatible AC adapter, try that. If not, try putting
> about 6 loops in the end of the adapter cable, & tape them into a bundle.
> This is a quick & dirty way of diminishing interference for some
> frequencies & might decrease the problem.

I have a Sony VAIO that picks up noise (when ITS power supply is plugged in)
when using an external microphone. I use your loop technique on the
microphone
cable with pretty good results. The VAIO also has S-Video output VIA a port
docking unit. I have NO issues using it under the same conditions I am
'trying'
to get the HP unit to work.

This supply is 18.5VDC 3.5A ... I could come up with a 16VDC 4A with little
problem ... You think that would be enough?/

> If not, your experiment won't take long to undo.
> There are also components in AC adapters (usually capacitors) that can
> go bad & produce just this kind of interference. There are things you
> can do to audio cables to filter out hum, but are beyond the scope of what
> I know.
>

Thanks for interest!


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