Hi everyone,

Perhaps someone would be kind enough to offer me some advice... I
repair electronic equipment but am still learning more about the
inverters used in LCD displays. Although I have repaired them before,
I've now come up against a problem for which I cannot find the
solution.

This monitor is actually mine. A Philips Brilliance 181AS 18.1" TFT LCD
monitor. Using a TDK TAD383 4-output inverter board, running on the 18V
input to the monitor. It displays a good image, but the white seems
off-colour. When compared to other LCD monitors, the whites on the
others seem bright and fresh, but this one seems grey or yellowish in
comparison. Perfectly usable, but not as bright as I would expect, with
both brightness and contrast set to maximum. Colour temperature
settings make no real difference.

I had originally had no backlight which was due to the inverter board
SMD fuse being blown. It was a 3A fuse but no fault could be found.
Current consumption is 1.6A currently when board is fully working. It
feeds 4 lamps and so has four outputs, two either end of the board,
each having its own circuitry but with one driver IC for each pair of
outputs either end.

There seems to be at least one transformer squealing on the board,
although this stops if the lamps from one end of the board are
disconnected. Maybe this is associated with the dullish display? When
those two lamps are reconnected and that half of the board starts up
again, the squealing returns and seems to be coming from all of the
transformers on the PCB. Touching the cores with the tip of an
insulated screwdriver gets sparks as I would expect, but touching one
particular transformer gets the sparks and then that half of the
circuit immediately shuts down, but this doesn't happen with the
others. Makes me wonder if something is wrong and altering the flux of
that particular transformer (by touching with tip of screwdriver) is
doing enough to cause the circuit to shut down because it isn't stable
or is only just within operating parameters?

I am planning to swap that transformer with another on the board and
see if touching the alternative transformer in that part of the circuit
still makes it shut down, or if this behaviour follows the transformer
which is currently shutting things down when touched.

Does anyone know if the high-frequency squealing and dullish display
are linked, and if so, what may be the cause? Is touching that
transformer and having the circuit shut down anything to do with it, or
is it just likely that it may be more susceptible?

I'd like to have this working properly, as it's supposed to have the
best brightness output of its class and is huge.

Many thanks to all.
James