[rescue] LCD monitor diagnosis

Phil Stracchino phil.stracchino at speakeasy.net
Sun Apr 16 16:31:24 CDT 2006

Don Y wrote:
> Phil Stracchino wrote:
>>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.

> Shine a light *into* the display (from the front) with a signal source
> connected.  You should be able to see an image if the panel itself
> is operating.

Ahead of you there.  As I said, the logic board is good, the screen's
good, there's picture, there's just no backlight.

> In most cases (that I have seen) the power supply and/or inverter
> for the CCFL's dies.  Most (?) inverters seem to run off 12V
> so check the power supply for a 12V feed to the inverters
> (often 2 inverters -- though could be on the same PCB).

Yup, looks like dual inverters on one board.

> Also, check for bad electrolytics.  Surprising how often
> you'll find "bulging" caps in the power supply.  Replace
> any you find (careful with polarity... I toasted an LCD
> that I *had* rescued by screwing up one cap  :<  ).
> And, unless there are a LOT of them, consider replacing
> ALL of them while you are at it.

Didn't see anything suspect on the inverter board.  Nor anything
abnormal-looking on the tubes themselves.

 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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