What could cause this h.linearity issue?!

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keropi
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What could cause this h.linearity issue?!

Post by keropi » May 31st, 2019, 1:47 pm

Hiya!

I have a 14" 15/31k dualsync monitor, when pin15 on vga connector is high then the monitor switches to 15k mode.
But I have this annoying linearity issue - right side is compressed:

Image

in VGA mode it's OK - you can't expand it to full screen , this is a 640x480 max resolution monitor and it has black bars around like all old vga monitors...

Image

So what I tried:
- replaced all electrolytic caps because there were some brightness/contrast issues which are now gone
- replaced all mylar caps in hopes the h.linearity issue will go away
- tried 6.6nf instead of 7.5nf for sweep capacitor C526 in hopes it would affect the issue - it did not
- tried adjusting the horizontal coil but the compressed part just remained the same

Image full-resolution: https://i.imgur.com/IIxNI63.png

Could it be:
IC101 TA8631N (LINEAR RGB PROCCESSOR)
IC402 TDA1675A (VERTICAL DEFLECTION CIRCUIT, most likely no)
IC401 HA11235 (Synchronous Signal Processing System that is also the horizontal oscillator among other functions)

Any ideas/tips will be greatly appreciated! Thanks!!! :D

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keropi
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Re: What could cause this h.linearity issue?!

Post by keropi » June 7th, 2019, 4:01 pm

well replaced all those ICs, no change :lol:
any ideas please share :awe:

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keropi
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Re: What could cause this h.linearity issue?!

Post by keropi » July 1st, 2019, 7:40 pm

Just an update to bring closure to the issue - with the help of online friends the issue was found : it is capacitor C521 that is a S Correction one in 15k mode.
Original is a 470nf/200v one - replacing it with a 2.2uF capacitor the monitor's 15k h.linearity improves and now it's tolerable. Not perfect but you cannot notice it during gameplay.
I count this as a win for this monitor :awe:

Image

monitor is not yet centered in the above pic but the improvement is quite visible

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geotrig
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Re: What could cause this h.linearity issue?!

Post by geotrig » July 1st, 2019, 10:44 pm

Yeah big difference there well done :awe:
Image

<trk>:I remember catching a big fat one and my friend said "throw it back in, that one already tastes like wood"

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