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Old 23 February 2013, 14:55   #1
trydowave
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RGB scart distortion.

Hi. I recently purchased this Amiga to RGB scart the other day and its giving me a slightly distorted picture on my panasonic quintrix TX-32PS1. Workbench bar warps slightly to the right and so does the white bards of any windows open. i'll be testing it on another crt as soon as i can but in the meantime does anyone know what could be going wrong?
Can it be corrected? Is the tv at fault or the scart lead or even the amiga?
The scart i eventually brought was this one:
http://www.ebay.co.uk/itm/1107994844...84.m1439.l2649

Heres a photo of the distortions. Sorry about the poor quality of the image. My camcorder has trouble with the screens flicker.
http://www.trydowave.com/amiga500rgb.web.htm

cheers
tony

Last edited by trydowave; 23 February 2013 at 15:24.
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Old 23 February 2013, 15:27   #2
john1979
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My panasonic quintrix does exactly the same. Some picture bending is normal on crts
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Old 23 February 2013, 15:31   #3
trydowave
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hi john... so theres no way to fix this then other than getting another crt?

Cheers
mate
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Old 23 February 2013, 15:39   #4
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On that quintrix no its just normal. I just bought this tv since i heard they make good monitors, if it doesnt suffer picture bending ill let you know. Although i think most tvs do it a little bit.


http://item.mobileweb.ebay.co.uk/vie...346587&trxId=0
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Old 23 February 2013, 15:47   #5
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If you turn the TV's brightness and/or contrast controls down, does that reduce the amount of distortion?
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Old 23 February 2013, 16:16   #6
trydowave
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yes... contrast seems to do it more than brightness
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Old 23 February 2013, 17:02   #7
demolition
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It's a very common thing in CRTs and using a low contrast setting usually helps. Some plasmas have a similar problem.
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Old 24 February 2013, 19:19   #8
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The effect you are seeing looks a bit like 'top curl'. This is caused by the TV missing synchronisation patterns in the vertical blank, which the Amiga does not output. Some TVs are better than others in this regard.

A not too technical discussion is here:
http://www.analog.com/static/importe...7357AN_850.pdf

Try an interlaced video mode and see if the problem persists.

Ian
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Old 25 February 2013, 10:42   #9
hooverphonique
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looking at the photo, I'd say this has nothing to do with vertical blank - even the icon further down the screen on the right causes the phenomenon..
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Old 25 February 2013, 10:47   #10
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I was wondering after reading Stedys link regarding synchronisation how this phenomenon works. If the above PDF were true, wouldn't we see something like this on LCD TVs?

I always wondered when I first had my Amiga why crt TV's do this. It doesn't matter what cable you use Comp/RF/RGB, the phenomenon is the same.
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Old 25 February 2013, 10:58   #11
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Quote:
Originally Posted by john1979 View Post
first had my Amiga why crt TV's do this. It doesn't matter what cable you use Comp/RF/RGB, the phenomenon is the same.
Maybe it has to do with the power supply in the CRT. If you have a line of high light intensity, the power supply voltage drops a bit due to the high long-term current draw. Maybe the voltage drop changes the trigger point for the hsync, shifting the picture horizontally?
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Old 25 February 2013, 11:17   #12
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Yes, it is CRT TV power supply regulation problem. It is not a fault (unless there are dried out capacitors)

Sudden big brightness change makes power supply to work harder (The brighter the image, the more current electron gun needs) and usually power supply can't handle it quickly enough = output voltage gets lower temporarily.

Lowered voltage = deflection coils can't deflect electron beam correctly = scanline's geometry and/or width changes.
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