mackenoly said:
I have a 15" viewsonic lcd monitor and would like to know if I need To
replace the back lites or the converter.Can anyone fill me in on which
to do. The back lites are far cheaper than the converter. If you use a
flashlight you can see the images on the screen.thanks much.
The CCFL lamps can have a service life of 15000 to 20000 hours. It
is most likely the inverter that is the problem, but don't ask
me how you are supposed to test it. (Leave the lamp connected to
the inverter - if you were going to power the inverter up, it
would be best if the inverter always had a load connected to it,
so the voltage doesn't climb too high.)
The cheapest experiment you can try, is disassemble the back of
the unit, and unplug and replug the connectors on the wiring
used. Sometimes the bad connection can be in the connectors
themselves.
In terms of running the inverter, you would think it would be
pretty simple. Like put in 12VDC and get out 1000VAC at 3mA for
a lamp (yes, it is high voltage). But some inverters also include
a control signal for the brightness, which in some cases involves
modulating the inverter at some lower frequency. Basically Pulse Width
Modulation, where the inverter is turned on and off hundreds
of times a second, and varying the ON time, to get whatever
the user desires for brightness. So if testing the inverter,
you'd need to apply power to it, but also understand what
is needed to keep the brightness signal happy. (If the designers
put a pullup resistor on the thing, it might run at full
brilliance, for example, if the brightness signal was
disconnected. You'd need to find a datasheet for the
inverter, to understand more about how it works.)
When reassembling the thing, be careful to put any foil or
insulating materials, back the way you found them.
Good luck and be careful,
Paul
(And no, I've never repaired one...)
