> I have a Gateway Solo 1450 laptop that presenting very dim, and to my
> eye, reddish cast, video. Also, there is a bit more flicker in it than
> there out to be. Hooking up an external monitor produces bright, clean,
> stable video.
> Any bets as to if this is a problem with the CCFL(s), inverter, or both?
> Thanks for your speculations.
If it was a reddish or brownish cast, and still moderately bright, it
would be the CCFL tube itself.
When the light level is weak and discolored, it could be one or both.
If it didn't light up some times (flaky), you'd suspect that was the fault
of the inverter.
When the characteristics of the CCFL tube change enough, that can also cause
a perfectly working inverter to enter protection mode.
Since inverters seem to be the most unreliable part of that subsystem,
I'd start there.
To measure the actual inverter voltage safely, isn't exactly easy.
The tube seems to be capacitively coupled to start with. They
don't use a DC connection. Perhaps the purpose is to prevent any
DC at all from appearing on the tube, to preserve the metal on
the electrodes inside. To get an accurate reading, you
might need to probe on the surface of the inverter, on the
inverter side of the coupling caps.
(See PDF page 8 here. CY1 and CY2 are examples of coupling caps on an inverter.
They're 27pF 2kV rated. Probing on the pin 1 side of the cap, would give
you a reading from the transformer.) http://www.diodes.com/_files/product...005_AP2001.pdf
The thing is, your multimeter might have a 1000VAC rating, just
barely able to cope with the voltages from the inverter. But
worst case, the inverter may be able to product 4000VAC unloaded,
like if the connection to the tube went open circuit for a moment,
and that would damage your meter. Some inverters can be
damaged if run open circuit (voltage goes too high, piezo element cracks).
As a consequence, if I had to do it, I'd probably want to borrow a
100:1 probe or the like. Picture of one here. I think over the
years, I've seen two of these, one in the physics lab in university,
another one at work for ESD testing. http://www.qsl.net/kh6grt/page2/test...nt/hvprobe.jpg
In the thread here, one of the participants notes that the inverter
is very load sensitive, and will enter protection mode at the drop
of a hat. Consequently, the design of the probe is quite critical.
The size of the coupling caps, from inverter to CCFL is in the pF
range, and any probe can't present more capacitive load than that.
So both the R and the C value of the probe can be important. The
C value would not be purposeful, but would be a leakage capacitance. http://www.eevblog.com/forum/general...af6328ef45c0be
They have an example here of how such probes are designed. You can
easily buy 22 megohm resistors, and put a whole bunch of them together
to build a larger resistance. That's what I used to use, for some
high voltage stuff I used to fool around with. If you were working
on really high voltages, such a circuit would need corona protection
(no rough metal edges, corona dope on exposed surfaces, that sort of
You might not have noticed, but I HATE high voltages. I've only
been thrown across the room once, by high voltage DC, and it left
a lasting impression. When you're on the floor, you can't remember
how you got there... :-) Once you look around the room, and see what
you were working on, then you can figure it out.
To their credit, the inverter making the 700-1000VAC runs at
25KHz. The higher the frequency, the more the current flows over
the surface of your skin. That is what prevents an inverter, from
having the truly nasty wallop DC can have. A danger with high
frequency AC, is it can burn you (burn a hole in your skin),
so even though you might not fly across the room, it can still
damage you. My high voltage device (flyback with voltage multiplier)
could light paper on fire, to give an example of the burning
potential. (The flyback isn't the circuit that threw me
across the room. That was something else I was working on.)
But that flyback thing drew around 36W on input, so about
10x more power was involved, than on an inverter.
Um, have fun ? And make sure there is nothing breakable
behind you, when you rocket across the room :-) I fell on
the cement floor in my basement. I'm just happy my head
didn't hit the floor.