LCD monitor: shimmering pixels one corner??
 

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/

LCD monitor: shimmering pixels one corner??
 

On Fri, 16 Apr 2010 19:06:46 -0400, Meat Plow wrote:

On Sat, 17 Apr 2010 08:52:17 +1000, Grant 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/

LCD monitor: shimmering pixels one corner??
 

On Fri, 16 Apr 2010 19:06:46 -0400, Meat Plow wrote:

On Sat, 17 Apr 2010 08:52:17 +1000, Grant 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/