[Tfug] LCD repair

[Bexley Hall]

Hi, Ronald,

--- Ronald Sutherland <ronald.sutherland at gmail.com>
wrote:

> 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.

Yes.  Typically one inverter per lamp.  (identical
designs)

> 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

That's possible.  The power supplies are internal for
these units so not as easy to swap out to test the
idea.  But, I can probably find an identical panel
to try it on...

> 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.

Understood.  I had hoped to *not* have to drag one
home for detailed testing but i tlooks like I won't
be able to avoid that  :<

I can also disconnect the inverters from the rest
of the electronics (since they are simply "bags"
as far as the rest of the design is concerned)
and see if the problem persists.

Thanks!
--don