[Tfug] OT: Troubleshooting a busted LCD TV (or Electrical Engineering for Dummies)

[Bexley Hall]

Hi, Chris,

--- On Fri, 8/22/08, Christopher Robbins <robbinsc at gmail.com> wrote:

> A friend of mine gave me a 17" Dell LCD TV that doesn't

You're *sure* its an LCD and not plasma?  (chances are it
*is* LCD)

> work anymore...Thing is getting power, but it doesn't output any
> video.

I don't mean to call you a liar... :>  But, are you
*sure* it isn't producing any video?  Tune it to a
decent station (below you say you get audio so you
should be able to verify that you have a channel 
tuned correctly).

Now, get a reasonably bright flashlight.  Shine it
*into* the display at an angle.  Look very carefully
and see if you see a faint image.  It helps if you have
another TV nearby on the same station so you know what
to expect (or, if you have a signal generator and
can ensure there are "color bars" that you could easily
recognize).

If you can see an image, then your problem is the
backlight.  (often an easy fix)

If you can't see any video, then you may have other
problems... :<

> You can see a green led when it's plugged in, but I'm
> not getting any video on it. He told me he can hear audio
> on it, but video hasn't been working at all.
> 
> I whipped out my trusty Craftsman multimeter to give the
> AC adapter a test...It's rated for 16V output, but it's only
> getting about 15.45V.

<shrug>  That's "nominally" 16V.  Depends on the characteristics
of the load and how well the supply is regulated, etc.

I assume you are measuring that 15.45V with the ac adapter
disconnected from the TV?

> My question is - can .55V really make that much of a difference?
> I assume you'd want to get an exact 16V out of the thing for it
> to work, but does it make that much of a difference?

Perhaps.  But, I suspect not.  I'm willing to bet you just
have a backlight problem.  (a lab supply is your friend if
you really think this is a problem)

> I'd like to figure out whether it could be just this
> before I dig deeper and deeper
> into the innards of this thing...Especially if a $20 power
> supply could mean the
> difference between a working and non-working LCD TV.

Do the flashlight test first.  If you have video but no
"light", chance are its a simple/inexpensive fix.

If you don;t see an image easily, try a different channel,
etc.  TV programs often don't have lots of contrast.  And,
without a backlight, you really are relying on contrast
in the image to help make it visible to you.

[contact me offlist if you would like]