On Wed, 28 Nov 2007 22:31:13 -0800 (PST), wrote:

I have a more than one tft screen where the backlight shuts off after
~2 seconds. By turning the monitor off and on again I get the
backlight to work for another 2s.
The screen functionality for the TFT matrix seems ok. And because the
tubes actually gives light even if only for 2s I assume they work. And
conclude it's the backlight inverter pcb.

My general understanding of this pcb is that it will take DC (usually
12V?) and chop it up and then transform it up by some means of smps. I
have access to multimeter and oscilloscope. Considering this there
should be a at least one power semiconductor acting as a switch.
Controller circuit and an output transforrmer.

The switch should have pulsed dc input and a pulsed voltage should
occour over the emitter-collector (or source-drain etc..). The
transformer primary should have pulsed dc aswell. Any break in this
chain should limit where the fault might be.
The output of the transformer (1300 kVrms?) is proberbly not a good
idea to measure as it's likely to blow the measurement equipment.

What strategy should one use..?

(I have been thinking about using a CCFL driver used for computer
decoration, but those lack brightness control..)

Two of the screens with these symptoms a
NEC LCD1810 (Backlight HIU-391C)
ViewSonic VE710b


If it has more than one bulb, then one of them is probably not
lighting at all. Most inverters will shut down unless all the bulbs
are working. I've never seen a bulb fail completely and cause this,
but one of the inverter sections often fails. To figure out which one
it is, power it up with only one bulb at a time connected until you
find the one that's not working. Then you at least know which part of
the inverter to focus on. To check the bulb, simply plug it into one
of the inverter's other outputs. Typical failures include failed
transformers, shorted transistors and diodes, and open fuses.
Andy Cuffe