Re: Studio-friendly LCD Display


"Arny Krueger" <arnyk@xxxxxxxxxx> wrote in message
news:A-OdnR2WCqFsTqjVnZ2dnUVZ_rzinZ2d@xxxxxxxxxxxxxx
"David Grant" <REMOVE_MEjmd_2003@xxxxxxx> wrote in message
news:XNWdnelQ4acw-6jVnZ2dnUVZ_jednZ2d@xxxxxxxxxxxx
No speaker. I'm not interested in any monitors with
built-in speakers. While I'm at it, I might as well
clarify that the noise IS coming from the lcd-monitor,
it's not induced noise into my speaker-monitors.
Probably the backlight inverter. When LED backlights
become a widely available option, they will provide a
silent alternative. But if it's a multiple of 60 Hz, it's the LCD driver
circuitry. I haven't heard this kind of noise, so I
can't comment.

After more playing around last evening, it is definitely
the backlight. Changing the refresh rate has no effect,
changing the brightness does. Interestingly the noise
disappears at brightnesses over 85 (which is bright
enough to warrant wearing sunglasses). It's a common
problem from what I've read on message boards.

Interseting. I did some rummaging around to see how they do backlighting
of desktop LCD displays and came up empty.

I did find info about laptops. Laptops use a dedicated switchmode supply.
It is a sine-wave output multimode supply that switches among 5(!) modes
for different brightness ranges. Desktops probably use a similar technique
since they probably can't play those kinds of games with the main
switchmode supply.

I once took a broken LCD display apart and seem to remember there being
two switchmode transformers on the power supply board, so this may all
fit.

It sounds to me like your LCD display's switchmode supply for the
backlighting is noisy in its topmost mode.

IOW, this is a product fault whose possibility is predictable from the
basic design.


A reasonable analysis.

Bob Morein
(310) 237-6511


.

Relevant Pages

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