STE VIDEO GHOSTING FIX

Various tweaks and fixes from video ghosting to audio fixes etc.
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exxos
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STE VIDEO GHOSTING FIX

Post by exxos » Mon Aug 28, 2017 11:34 am

 
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While I was developing my replacement AtariPSU I noticed the video quality improved immensely. However, I still saw some "ghosting" on the display which baffled me for a few hours. While ghosting can be other factors, such as bad video cable, ora bad LCD TV, for me the problem was on the Atari itself. On the left is the image before my fix, and on the right is after my fix. The left image shows ghosting to the right of the Atari Fuji and at the ends of the black box lines. While the ghosting is faint, it can still be seen clearly compared to the image on the right. Thankfully the fix is a easy one..NOTE - This mod was to fix RGB/scart issues and has not been tested with RF or Composite video signals.  

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Near the top left of the simms there is a yellow capacitor (C411) whichneeds more capacitance across it. The odd-ish thing is, R544 is actuallya 8V regulator feed from the 12V rail. Normally I would have expectedgood regulation there, and it is, but its still not good enough to solvethe video problems.

The results are...

1uF ceramic doesn't fully solve the ghosting problem.

10uF electrolytic probably 95% solves the problem.

47uF seems to work best, may improve a couple % with the 1uF in addition.

So a 47uF capacitor with the possible addition of a 1uF ceramic seemsto fix this issue. Larger values than 47uF can be used, but I would notrecommend going below 47uF. Like I keep saying over and over in otherpages on my site, you NEED low ESR capacitors otherwise "any oldcapacitor" will not work! Look towards Panasonic FR range of capacitors.I generally have a stock of all sorts of values of capacitors in my storeif anyone needs some.

That's it! Enjoy your ghost free display :)

Another couple of images of ghosting issues (and fixed ) on a STE I wasservicing today..
 
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MSTE VIDEO GHOST FIX (WIP)

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I had a MSTE in for repair so I looked into solving the ghosting issue.It was only slight on this machine, so capturing a image proved difficult.However with soldering a low ESR 10uF capacitor across C506 as shown inthe above image removed what little ghosting I saw.

If anyone can verify this and take images on their own MSTE then it wouldhelp.

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