J
jdiaz5513
- Jan 1, 1970
- 0
I'm an EE, and would like a technical explanation from someone who
understands the inner workings of an LCD display.
Just recently acquired a VERY nice looking 24" LCD display
(Westinghouse L2410NM) for free. It could be important to note that
this model uses an MVA panel, and not a TN like most other monitors.
The acrylic panel on the corner was shattered when I got it, so I
neatly removed it. I started enjoying the display for a few days until
the nightmare began...
First the symptoms:
After a few hours of powering up (but not always?!), the rear
circuitry and top area of the LCD gets very hot, way hotter than I'd
expect from an LCD. From the heat rising up, I would estimate
something is hitting around 60C in there. The backlights are located
on the far left and right sides, and they are not the source of the
heat in this case. There is no fan, just grilles to passively
dissipate heat. The mains power supply is integrated into the back of
the LCD. I noted an audible high frequency noise that starts as soon
as power is applied (without actually turning the monitor on), but
that noise is apparently normal for this LCD model.
Once it gets hot enough (sometimes it will not heat up at all and run
for 24+ hours), the image starts distorting vertically, with
horizontal black lines appearing randomly throughout the image.The
distortion is the most severe at the bottom, and a chunk of the top
area remains somewhat visible. Moving the mouse around shows that the
screen is still refreshing at 60Hz.
Soon after this (30 sec to 1 min), the entire image fades slowly and
ghosted afterimage of the previous colors appear, which seems to
eventually turn to orange. Image: http://img4.imageshack.us/img4/1818/mediacardblackberrypictj.jpg
Pressing in on the top middle area of the LCD panel (where the FPC
ribbon cables are) temporarily brings things back to normal. Sometimes
it will "snap" back into position and the image will remain stable for
quite a while (even a few days). Eventually, though, it reaches to a
point where no amount of pressure will bring the image back until the
monitor is left unplugged for hours.
After first seeing all this nonsense, I went ahead and tore the thing
apart. My targets were the 2 FPC cables at the top feeding the image
to the panel - I reseated them to the best of my ability but this did
not change anything. Mind you - I've tried all the obvious: swapped
video cables, checked AC line voltage/ripple, changed output sources,
used different inputs on the LCD, etc. The only thing I didn't try was
forced cooling, but isn't that a little ridiculous?
My guesses:
*There is a history of abuse, so the problem is likely to be physical
and not due to a faulty component.
*Possibly damaged FPC cables.
*Poor voltage regulation from the power supply (seems unlikely b/c of
the effect of pressing on the top).
*Cold/loose joint in the power supply.
*Loose BGA connection on the video processing board (I hate BGA's,
personally).
*Cold/broken SMT solder connections on the ZIF connector that feeds
the LCD panel itself.
*Broken flexible cable feeding the pixels themselves (worst case
scenario!).
The only consistent signs I see is that pressing at the top usually
alleviates the symptoms, there is a lot of heat present when the image
does fail, and leaving the LCD unplugged for some time will always
clear it up.
I work at a decently equipped shop (oscilloscope, decent DMM, heat
gun, etc) with plenty of spare components and I can solder even tiny
SMT pins without a problem, but I'd love some insight as to where I
should poke around before I take the effort to haul it over to the
shop. If my effort is futile it would save me a lot of headache to
hear that. I know there must be at least someone out there has seen
this before.
Thanks!
-JD
understands the inner workings of an LCD display.
Just recently acquired a VERY nice looking 24" LCD display
(Westinghouse L2410NM) for free. It could be important to note that
this model uses an MVA panel, and not a TN like most other monitors.
The acrylic panel on the corner was shattered when I got it, so I
neatly removed it. I started enjoying the display for a few days until
the nightmare began...
First the symptoms:
After a few hours of powering up (but not always?!), the rear
circuitry and top area of the LCD gets very hot, way hotter than I'd
expect from an LCD. From the heat rising up, I would estimate
something is hitting around 60C in there. The backlights are located
on the far left and right sides, and they are not the source of the
heat in this case. There is no fan, just grilles to passively
dissipate heat. The mains power supply is integrated into the back of
the LCD. I noted an audible high frequency noise that starts as soon
as power is applied (without actually turning the monitor on), but
that noise is apparently normal for this LCD model.
Once it gets hot enough (sometimes it will not heat up at all and run
for 24+ hours), the image starts distorting vertically, with
horizontal black lines appearing randomly throughout the image.The
distortion is the most severe at the bottom, and a chunk of the top
area remains somewhat visible. Moving the mouse around shows that the
screen is still refreshing at 60Hz.
Soon after this (30 sec to 1 min), the entire image fades slowly and
ghosted afterimage of the previous colors appear, which seems to
eventually turn to orange. Image: http://img4.imageshack.us/img4/1818/mediacardblackberrypictj.jpg
Pressing in on the top middle area of the LCD panel (where the FPC
ribbon cables are) temporarily brings things back to normal. Sometimes
it will "snap" back into position and the image will remain stable for
quite a while (even a few days). Eventually, though, it reaches to a
point where no amount of pressure will bring the image back until the
monitor is left unplugged for hours.
After first seeing all this nonsense, I went ahead and tore the thing
apart. My targets were the 2 FPC cables at the top feeding the image
to the panel - I reseated them to the best of my ability but this did
not change anything. Mind you - I've tried all the obvious: swapped
video cables, checked AC line voltage/ripple, changed output sources,
used different inputs on the LCD, etc. The only thing I didn't try was
forced cooling, but isn't that a little ridiculous?
My guesses:
*There is a history of abuse, so the problem is likely to be physical
and not due to a faulty component.
*Possibly damaged FPC cables.
*Poor voltage regulation from the power supply (seems unlikely b/c of
the effect of pressing on the top).
*Cold/loose joint in the power supply.
*Loose BGA connection on the video processing board (I hate BGA's,
personally).
*Cold/broken SMT solder connections on the ZIF connector that feeds
the LCD panel itself.
*Broken flexible cable feeding the pixels themselves (worst case
scenario!).
The only consistent signs I see is that pressing at the top usually
alleviates the symptoms, there is a lot of heat present when the image
does fail, and leaving the LCD unplugged for some time will always
clear it up.
I work at a decently equipped shop (oscilloscope, decent DMM, heat
gun, etc) with plenty of spare components and I can solder even tiny
SMT pins without a problem, but I'd love some insight as to where I
should poke around before I take the effort to haul it over to the
shop. If my effort is futile it would save me a lot of headache to
hear that. I know there must be at least someone out there has seen
this before.
Thanks!
-JD
