[rescue] LCD monitor diagnosis

Don Y dgy at DakotaCom.Net
Sun Apr 16 18:00:17 CDT 2006

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

>> 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.

In most LCD monitors, the inverter board is separate and
can be replaced (it's more of a commodity than the LCD itself!)

>> 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.

I assume the power supply (external) just provides
regulated supplies to the "monitor"?  I.e. there's
some sort of oddball connector (not an AC power inlet)
on the monitor that has DC voltages on it.  Can you
verify that you have +12VDC somewhere on that connector?
(i.e. that the 12V in the power supply hasn't gone
into current limit because of a failure on the 12V *load*)
If you *can't*, you might try unplugging the inverter
(with power off  :> ) and try again to verify the
inverter isn't loading down the supply.  This *should*
be safe to do as most power supplies regulate off the
+5 load (which is still intact even with the inverter

Can you see 12V on the inverter itself?  If nothing
else in the panel is using +12V, then there *have* to be
some (bulk) decoupling capacitors there someplace.
Make sure they haven't gone south on you...


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