[mythtv-users] AC Hum/ weird lines, ETC (was Plextor Convertx CPU Usage)

Brian Wood beww at beww.org
Tue Apr 8 15:27:34 UTC 2008


On Apr 7, 2008, at 10:01 PM, Steve Peters - Priority Electronics wrote:
>
>
> My Power Supply is the included supply that comes with the IN WIN
> IW-V605T2.J350SL Black-Siliver Steel ATX Mini Tower Computer Case
> http://www.newegg.com/Product/Product.aspx?Item=N82E16811108043
>
> In the system, I have an nvidia 7300lt, 1gb ram, 2 of the pvr-500  
> cards, no
> optical drive, but 2 ide hard drives (I don't think I'm overloading  
> it).
> Could it be something with the power supply or motherboard?
>
> Any my mother board is the GIGABYTE GA-945GZM-S2 LGA 775 Intel 945GZ  
> Micro
> ATX Intel Motherboard
> http://www.newegg.com/Product/Product.aspx?Item=N82E16813128033
>
> Also, the lines which look like about 50 light gray vertical lines  
> going
> through the picture across the entire screen don't happen with the tv
> tuners. But, when the tv tuners have bad reception (us cable), but  
> when I
> unplugged the system fan (default one that comes with that system,  
> plugs
> into the motherboard) the reception gets better, also, the lines  
> decrease,
> but don't totally go away.


This could be a LOT of things, including interference from stray  
signals floating around in your case. The fan issue is a clue, but the  
improvement might be from removing the electrical load of the fan, or  
from the (presumably unshielded) fan wires propagating signals around  
the case (basically acting as an antenna).

This sort of problem can sometimes be corrected, or at least improved,  
by moving cards and cables around.

I once had interference with a Hauppauge card that was fixed by  
putting a dab of solder on each side of the tuner shield can, but  
since you say the problem doesn't happen with the tuners this is  
probably not your problem.

Basically look at your grounding, shielding, lead dress and general  
good practices. Make sure all of the mobo screws are installed and are  
tight (I have seen machines with only 2 or 3 of the 9 or more mobo  
screws installed). Re-seat cards to make sure they are firmly installed.

>
>
> Also, both cards have different results, one has better reception on  
> the
> cable input and less lines on the svideo and composite inputs.
>
> Lastly, every now and then, like every 10 to 15 minutes or so, the  
> cable
> input's sound pops and goes mute for a half second or so, then goes  
> back to
> normal. Very strange. This does not happen on the svideo with rca  
> sound
> inputs.

Perhaps far fetched, but this could be from a "sweep generator" used  
by the cable company for system maintenance. These used to just run  
every few seconds, but today most systems have a way for the tech to  
trigger the sweep. This is a signal that sweeps from the bottom to the  
top of the frequency range, and might cause you that sort of problem  
when it passes through the channel you are receiving.

beww



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