[rescue] LCD monitor diagnosis

Phil Stracchino phil.stracchino at speakeasy.net
Sun Apr 16 14:54:16 CDT 2006

OK, folks, here's the scoop.

I have  ViewSonic VA800 pivoting LCD monitor.  I've obtained a new power
supply for it, and determined that all the logic is perfectly operable,
the screen is good, but the backlight is completely dead.

The backlight consists of four 364mm CCFL tubes, two at the top and two
at the bottom of an acrylic scatter plate, all driven off the same
inverter board.  None if the four tubes shows any visible indication
whatsoever when the monitor is powered on.  I believe the two tubes in
each set are wired in parallel.

Is it reasonable and realistic to assume that all four CCFL tubes would
have failed?  My guess here is actually that I'm looking at a bad
inverter.  Given that my DMM only goes to 750V on AC and the inverter
should probably be putting out more like 10kV, can anyone suggest any
way I can actually test to determine whether the tubes or the inverter
are at fault?

(At this point, I have a pretty strong hunch it's the inverter.  But I'm
not 100% certain.)

 Phil Stracchino                     Landline: 603-886-3518
 phil.stracchino at speakeasy.net         Mobile: 603-216-7037
 Renaissance Man, Unix generalist, Perl hacker, Free Stater

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