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Old 9th Jul 2018, 4:44 pm   #1
srijibmandal
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Default Pattern in Screen Video CRT colour TV

I am getting light to dark gradient bands on the screen when I select TV mode, on AV mode it looks fine until i apply the video signal from the set top box AV connector. I have attached the picture of the video screen on TV mode. It a Samsung CRT TV.

Also i get sinusoidal waves running from left bottom corner to right top corner. Any suggestion will be helpful
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Old 9th Jul 2018, 4:58 pm   #2
G6Tanuki
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Default Re: Pattern in Screen Video CRT colour TV

How's the STB signal being applied to the TV? SCART? Composite video? RF Modulated?

If it's via a RF modulator this sort of on-screen thing can occur if the STB/TV are interconnected with a cheap poorly-screened coax cable which picks up RF from external sources (like another TV transmitter) - Sometimes retuning the STB output and TV to another channel can help.

If you're using SCART it's worth checking that the SCART connectors are both fully 'home' in the sockets - the connectors are horribly designed and can work loose, sometimes causing permanent damage to the sockets [don't push a SCART-connected TV/VCR/STB up against the wall...].
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Old 9th Jul 2018, 5:11 pm   #3
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Default Re: Pattern in Screen Video CRT colour TV

It is also possible that you have interaction between the cables in the Scart lead, that is if you are using one. They need to be fully screened to eliminate this problem. John.
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Old 9th Jul 2018, 6:45 pm   #4
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Default Re: Pattern in Screen Video CRT colour TV

I had a similar problem caused by a 'hum loop' between the audio and video connections of a tv connected to a freeview box, dvd player and PVR. I put it down to beat interference between the SMPSUs .

Cheap scart leads use plain old multicore with one overall screen which really do lead to poor noisy pictures
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Old 9th Jul 2018, 7:02 pm   #5
Hampus
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Default Re: Pattern in Screen Video CRT colour TV

If it is connected with a SCART-lead, can this be your problem?

http://www.stevelarkins.freeuk.com/s...terference.htm

My TV had issues with ghosting and rolling lines until I found that info and cut out pin 19.
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Old 9th Jul 2018, 9:28 pm   #6
Graham G3ZVT
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Default Re: Pattern in Screen Video CRT colour TV

SCART is a very European connector, I doubt the OP has ever seen one.
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Old 10th Jul 2018, 1:19 pm   #7
srijibmandal
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Default Re: Pattern in Screen Video CRT colour TV

Quote:
Originally Posted by G6Tanuki View Post
How's the STB signal being applied to the TV? SCART? Composite video? RF Modulated?
I am using composite video cable. as mentioned if it is 50Hz hum then how do i remove it, is it anything to do with the filters on the Chassis ?

Quote:
Originally Posted by McMurdo View Post
I had a similar problem caused by a 'hum loop' between the audio and video connections of a tv connected to a freeview box, dvd player and PVR. I put it down to beat interference between the SMPSUs .
STB is connected via composite cables.
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Old 11th Jul 2018, 11:17 pm   #8
McMurdo
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Default Re: Pattern in Screen Video CRT colour TV

Unlikely 50hz as this is a very distinctive pattern. Much more likely smpsu noise being picked up through a hum loop (I was using the term analagous to an audio hum loop).

I'm not well up on the last generation of CRT designs but in Europe many smpsu's were synch'ed at horizontal frequency to minimise crosstalk artifacts. Obviously this doesnt work across multiple smpsu-equipped accessories.

In my case the noise was shown as a slowly travelling, faint vertical noise bar on a DVD playback with a very faint ghost of live TV superimposed across the raster. I solved it by lifting the grounds at one end of the scart lead from the PVR to the TV, this cured the DVD noise problem, the DVD being connected to the TV via S-Video and Stereo phono.
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