LCD monitor: shimmering pixels one corner??
in [Repair]
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From: Grant on 16 Apr 2010 18:52 Hi there, I'm repairing a CTX S760A LCD monitor, replaced all the caps in the switching regulator section as they were bulging. That got the monitor going for more than a second :-) Now the LCD works fine, apart from an odd shimmering pixel effect in top right hand corner after the thing warms up for a few minutes. A photo of these shimmering pixels is at: http://grrr.id.au/casual/shimmering-pixels.jpg I've not seen this effect or fault before. More info: LCD monitor CTX S760A Main board CTX S962A/S762A REV:C00 Power board S7 Series Power B/D REV:A10 (replaced switcher section electro caps) LCD module AU Optronics Model: M170NE05 V.1, Made in China Measurements Screen Off V On V 12V 13.37 12.42 5V 4.94 4.97 3.3V 3.35 3.34 LCD Power 5V 0 4.81 Monitor okay when cold, pixels start shimmering in top-right corner after some minutes. Show up on black background, display is normal on bright background but pixels show on single colour background. Anyone seen this? What fix? The service manual is available on the 'net, but the one I found is only module level, no circuit diagrams. Thanks, Grant. -- http://bugs.id.au/
From: Grant on 17 Apr 2010 16:58 On Fri, 16 Apr 2010 19:06:46 -0400, Meat Plow wrote: >On Sat, 17 Apr 2010 08:52:17 +1000, Grant <omg(a)grrr.id.au>wrote: > >>Hi there, >> >>I'm repairing a CTX S760A LCD monitor, replaced all the caps in the switching >>regulator section as they were bulging. That got the monitor going for more >>than a second :-) >> >>Now the LCD works fine, apart from an odd shimmering pixel effect in top >>right hand corner after the thing warms up for a few minutes. >> >>A photo of these shimmering pixels is at: >> >> http://grrr.id.au/casual/shimmering-pixels.jpg >> >>I've not seen this effect or fault before. >> >>More info: >> >>LCD monitor CTX S760A >>Main board CTX S962A/S762A REV:C00 >>Power board S7 Series Power B/D REV:A10 (replaced switcher section electro >> caps) >>LCD module AU Optronics Model: M170NE05 V.1, Made in China >> >>Measurements Screen >> Off V On V >> 12V 13.37 12.42 >> 5V 4.94 4.97 >> 3.3V 3.35 3.34 >>LCD Power 5V 0 4.81 >> >>Monitor okay when cold, pixels start shimmering in top-right corner after some >>minutes. Show up on black background, display is normal on bright background >>but pixels show on single colour background. >> >>Anyone seen this? What fix? >> >>The service manual is available on the 'net, but the one I found is only module >>level, no circuit diagrams. >> >>Thanks, >>Grant. > >If you could identify what was responsible for driving the LCD matrix >you could use some freeze spray and chill it. There might be some >additional circuitry around the panel embedded into the edge >connectors. Hard to say without a look. I didn't want to get that close to the screen. I've added a photo of the board feeding the LCD edge connector in that corner, there's a trimpot there I have no idea what it does. It's underneath a dozen screws again :( Also, since the LCD module is only getting 4.8V I thought of boosting the 5V rail to say 5.15V (5V is slightly low at the moment) to compensate for the LCD module's power switch drop? So far I've not seen anything temperature related in the measurements. LCD not being able to show black demonstrates a lack of drive voltage, but I don't have enough info on these big LCD modules to know what an umpteen phase drive waveform should look like. I'll drop more images into http://grrr.id.au/odd-lcd/ shortly. Thanks, Grant. -- http://bugs.id.au/
From: Grant on 6 May 2010 18:08 On Fri, 16 Apr 2010 19:06:46 -0400, Meat Plow wrote: >On Sat, 17 Apr 2010 08:52:17 +1000, Grant <omg(a)grrr.id.au>wrote: > >>Hi there, >> >>I'm repairing a CTX S760A LCD monitor, replaced all the caps in the switching >>regulator section as they were bulging. That got the monitor going for more >>than a second :-) >> >>Now the LCD works fine, apart from an odd shimmering pixel effect in top >>right hand corner after the thing warms up for a few minutes. >> .... >If you could identify what was responsible for driving the LCD matrix >you could use some freeze spray and chill it. There might be some >additional circuitry around the panel embedded into the edge >connectors. Hard to say without a look. I decided it was too risky to look at the chips in the ribbon cable. Besides there's not much I could do about a problem with the ribbon connection to the long, narrow chips, or ribbon to LCD connection, is there? Added some resistors around the switching regulator feedback (ubiquitous TL431 into opto circuit) to improve the 5V and 12V rails (5V up 3.5%, 12V down 3.5%), with no effect on the display problem. There was a trimpot up in that corner but it was a contrast setting, also no effect on the shimmering pixels. Grant. -- http://bugs.id.au/
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