My in-laws own the above mentioned TV (TV currently in my house with the back off) and, over the last year or so, the picture has got very dark, even with Backlight and Brightness up at Max. It is the same irrespective of source: Digital Tuner, Analogue via SCART or HDMI.
I haven't taken it apart sufficiently to check that all of the tubes are OK, but there is no horizontal 'banding' that I would expect from such a failure (or are the diffusers that good?), in fact, on uniform pictures one can detect a very broad, and barely dicernable, vertical 'banding' Darker/Lighter/Darker/Lighter/Darker/Lighter.
I really have no idea whether the backlight is not actually at full brightness, or that the backlight is OK, but the screen is not letting enough of it through, or what.
I believe that the LCD screen is driven from two long, thin boards along its top edge, and that they are, in turn, driven from the single 'Timer Control' board: such two-fold symmetry would not seem to line up with the three-fold repetition of the dark banding, so this makes me think that it may not be the screen.
Looking at the Invetor Board (E206453 V144-X01) I can see that the PWM controller is a OZ964. Having found the datasheet for the OZ964, the Reference Circuit for driving CCFL tubes states that the VADJ signal (which goes to the 'DIM' input [pin 14 of the chip]) is 2.1V for Maximum Brightness and 0.6V for Minimum Brightness. Now I have measured the correct supply voltage (24V) on the Inverter Board connector, and measured the top pin of that connector as 0.65V when the tubes are dimmed for a 'no picture' state, and 2.917V when at their brightest. I have been too scared to measure pin 14 directly (tiny pins, risk of shorting), but may eventually have a go.
