[Tfug] LCD repair

[Ronald Sutherland]

I've not worked much with CCFL, but basically know how they work. The CCFL
power supply is converting DC to AC (for example 12V to 300VAC at 400Hz), it is
often a self oscillating (royer oscillator) circuit. Most power supply's
have a fair amount of safety circuits that keep them and there loads from
billowing out to much smoke, unfortunately this is where I have to start
guessing. 1 -2 sec is to fast for most heat related protection, and to slow
for input current limit protection,  I'm going to make a wild guess that the
DC feed (input to CCFL) is not holding up under the startup load, the power
supply that converts the 115AC from the wall to DC (12V) for the display
electronics and CCFL converter. To check for such things I would put a
oscilloscope on the DC (12V) line and see if it sags or hiccups during
startup, a DMM may also see it but may not.

On Mon, May 12, 2008 at 3:49 PM, Bexley Hall <bexley401 at yahoo.com> wrote:

> Hi,
>
> WorldCare routinely gets LCD displays as donations.
> These are most often resold in the store although some
> with cosmetic problems are retained for use in-house.
>
> Many are working.  Many are not.  :<
>
> Of course, my concern is with those that are *not*!
>
> I think they can be grouped in three categories:
> - CCFL's dead but the panel itself appears operational
> - Unit powers up, video present, then power cycles
> - dead as a doornail
>
> Those in the first category I can fix.  Those in the
> last category are *sometimes* worth the effort.  But,
> those in the *second* category I have avoided, thus
> far.  They *seem* like they should be an easy fix
> (power supply problem?) since they "work" for that
> 1-2 second period before the supply cycles.
>
> Any pointers?
>
> (Note WC doesn't have much in terms of repair
> capabilities and I don't want to be hauling stuff
> home for repair if there isn't a *good* chance
> of success)
>
> Thx!
> --don
>
>
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