Hi,
I've just got hold of a Panasonic Viera 49” screen that seems to have a backlight issue.
The screen turns on fine and runs for a few minutes and then appears to turn off, however it looks like it's just the backlight that goes off, everything else seems ok (sound is still there if I have enough time to get iPlayer started.)
I've done a bit of initial investigation and I suspect the LED driver (MP3349S) on the 17IPS20 power board, as it appears to get really quite hot … pushing 60degrees when measured from the other side of the board, so it's going to be significantly hotter than this, therefore I'm thinking it's some kind of thermal shutdown.
The time to turn-off does also seem to be impacted by how recently it's been on, so it does support being thermally related.
But … in this forum people with similar behaviour seem to be pointed at LED failures in the backlight.
In this TV these seem to be two separately powered strings of LED's, I've run each string independently for a good half an hour each using a current source, I've only gone to 8mA (because I'm paranoid) and this is achieved with a fairly constant 86V, no changes with time, no flickering, no indication of any problem. (Although I do acknowledge I'm not driving it very hard.)
The other thing to mention is that the connector where the backlight cable joins the power board is quite deformed and has some small indications of charring. My guess is that there was some kind of poor connection, leading to arcing, leading to damage to the driver.
Does this all sound reasonable? Or am I missing something?
I'm really trying to avoid dismantling the panel, so I might be clutching at straws, but the LED's do all seem to be ok, and swapping the driver chip is pretty simple in comparison.
Thanks for any help!
Lee.
I've just got hold of a Panasonic Viera 49” screen that seems to have a backlight issue.
The screen turns on fine and runs for a few minutes and then appears to turn off, however it looks like it's just the backlight that goes off, everything else seems ok (sound is still there if I have enough time to get iPlayer started.)
I've done a bit of initial investigation and I suspect the LED driver (MP3349S) on the 17IPS20 power board, as it appears to get really quite hot … pushing 60degrees when measured from the other side of the board, so it's going to be significantly hotter than this, therefore I'm thinking it's some kind of thermal shutdown.
The time to turn-off does also seem to be impacted by how recently it's been on, so it does support being thermally related.
But … in this forum people with similar behaviour seem to be pointed at LED failures in the backlight.
In this TV these seem to be two separately powered strings of LED's, I've run each string independently for a good half an hour each using a current source, I've only gone to 8mA (because I'm paranoid) and this is achieved with a fairly constant 86V, no changes with time, no flickering, no indication of any problem. (Although I do acknowledge I'm not driving it very hard.)
The other thing to mention is that the connector where the backlight cable joins the power board is quite deformed and has some small indications of charring. My guess is that there was some kind of poor connection, leading to arcing, leading to damage to the driver.
Does this all sound reasonable? Or am I missing something?
I'm really trying to avoid dismantling the panel, so I might be clutching at straws, but the LED's do all seem to be ok, and swapping the driver chip is pretty simple in comparison.
Thanks for any help!
Lee.
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