Dropped flat screen

This is the place for any magazine-related discussions that don't fit in any of the column discussion boards below.
Post Reply
psycho
Posts: 388
Joined: Thu Jan 10, 2008 8:13 pm
Location: Northwest Indiana
Contact:

Dropped flat screen

Post by psycho » Sun Sep 11, 2011 7:14 pm

An employee at the local school has an LCD tv that was dropped. LN37B530 blah blah blah... The set turns on and has audio but no picture. I am fairly sure that the problem is with the backlight. I have never worked on one before but I would love to fix this for him so I can learn from the experience. What do the bulbs look like and can they be had easily (and cheaply)? Also, what is the easiest way to troubleshoot the backlight and inverter?

Thanks!
Kevin

User avatar
Externet
Posts: 1844
Joined: Fri Feb 01, 2002 1:01 am
Location: Mideast USA
Contact:

Re: Dropped flat screen

Post by Externet » Mon Sep 12, 2011 8:02 am

Very pessimistic...

You are "fairly sure that the problem is with the backlight"...
In a darkened room, bring a flashlight touching against the screen. If only backlights are non working, an image will be discernible that way. If no image, needs major troubleshooting. Cracked display glass ----> keep as replacement parts and forget it.

Bulbs look like ~ 1/8" glass long and fragile tubes at the perimeter of the screen, held inside a shield and very tricky to remove/reinstall without breaking something else. Price comes in all flavors from different providers on the net.

The inverter needs to be checked for -usually 12V in and ~1000V AC out- when its control line enables it to turn on.

Miguel
- Abolish the deciBel ! -

psycho
Posts: 388
Joined: Thu Jan 10, 2008 8:13 pm
Location: Northwest Indiana
Contact:

Re: Dropped flat screen

Post by psycho » Mon Sep 12, 2011 9:16 am

I will check that out - thanks! I would take it that you are leaning towards something worse than simple backlights?

Thanks again,
Kevin

User avatar
Janitor Tzap
Posts: 1475
Joined: Sat Aug 12, 2006 5:17 pm
Contact:

Re: Dropped flat screen

Post by Janitor Tzap » Mon Sep 12, 2011 11:00 am

I agree with Externet,

So far as doing the Flashlight test.

If you can make out an image.
Then it maybe just broken bulbs.
Or even better, a broken connector to the bulbs. :)

But remember: this LCD was dropped.
Not only do you need to repair the connections, or replace the broken bulbs.
But you have to repair the case as well.
The case supplies support for the glass, and the internal electronics.

The biggest problem though is being able to easily work on it.
Most shops that service flat screen LCD's have special Jigs to hold it,
while you work on it.
Just the small jigs for 19" and smaller LCD's cost around $200 or more.

Also, cost of parts will be a factor.
If the parts alone go over half the cost of a new LCD of the same size, and all its features.
Chuck it.
{Unless someone just gave it to you for free, and you want it for yourself.} :razz:
Because if you check around.
You could probably find another used working LCD for the cost of the repairs for this damaged one.

Sorry, for being so negative about fixing these LCD's.
But unless you have right tools for working on them.
It can be a nightmare.

So far I've been lucky....
I've only been working on a few Laptops that had connector problems to the screen.

I did look at some early Gateway LCD 15" Monitors.
But everyone of them had suffered Inverter failure.
And since they were already 5 years old.
They weren't even worth the time to fix. :(


Signed: Ensign Janitor Tzap

User avatar
dacflyer
Posts: 4506
Joined: Fri Feb 08, 2002 1:01 am
Location: USA / North Carolina / Fayetteville
Contact:

Re: Dropped flat screen

Post by dacflyer » Mon Sep 12, 2011 7:20 pm

i have salvaged some inverters out of flatbed scanners. and the tubes..
the tubes are "cold cathode" lamps, sort of like a mix of neon and fluorescent single electrode on each end like neon, and glows like fluorescent.
the inverters i have used to test CC tubes.
12v in. and HV out.
for cheap you can find stand alone CC inverters. you can use that to test the tubes.
might have to find a way to connect to them though.
as far as replacing the tubes.. that can be very hard to impossible..
so be sure to test well before you take the dip..
if the screenis broke, it can cost 2/3rds the price of a new tv.. and sometimes not available at all..
and if you can find it.. it might be coming from china. and freight is not cheap.
good luck :)
i still like my boob tubes..

psycho
Posts: 388
Joined: Thu Jan 10, 2008 8:13 pm
Location: Northwest Indiana
Contact:

Re: Dropped flat screen

Post by psycho » Mon Sep 19, 2011 7:16 pm

Possible good news. First, and I should have said this before, the case is not broken - I cannot tell where it hit. But better than that, I did the little test that externet told me about and we could see an image! I moved the maglight around to several parts of the screen and we can't see anywhere where it is cracked.

So, since I see an image, does that mean that the glass is NOT cracked (i.e. is it an all-or-nothing test result)???

Thanks!
Kevin

User avatar
Janitor Tzap
Posts: 1475
Joined: Sat Aug 12, 2006 5:17 pm
Contact:

Re: Dropped flat screen

Post by Janitor Tzap » Mon Sep 19, 2011 9:25 pm

psycho wrote:Possible good news. First, and I should have said this before, the case is not broken - I cannot tell where it hit. But better than that, I did the little test that externet told me about and we could see an image! I moved the maglight around to several parts of the screen and we can't see anywhere where it is cracked.

So, since I see an image, does that mean that the glass is NOT cracked (i.e. is it an all-or-nothing test result)???

Thanks!
Kevin
First off....
Check every part of the screen!
Make sure there has been no damage to the LCD glass.
Even if it is cracked, some areas may still work.
But any dead area's on the screen will be hard to see, or make out.
If you can, connect up a Color Bar Generator.
Set the Generator for a White, or Gray Screen.
Thus, with the flashlight carefully go over every square inch of the screen.

Once your fairly sure the LCD glass is okay.
Then get a blanket, double fold it.
Place the Television on it, face down.
Now start removing the back cover.
This can be tricky, as you may find some parts of the set are mounted to the back cover.
IMPORTANT: Take pictures of what your doing as you disassemble the set.
Have small bags on hand to put the screws in and label them.
If you don't have a camera handy.
You can do simple diagrams of the set.
Showing what screws went where.
Connector wire diagrams.
{Even if you have a Camera, having a diagram is a great help!}

With the back cover removed, look for the CFL lamps.
Pay attention to the ends where the wire attaches.
See if it is loose, or the end of the glass tube has snapped.
Check the ends to see if they are blackened.
This is an indication that the seal on of the lamp has failed.
If you can't see any physical damage.
The next step is to carefully remove the shielding around to tubes, checking for breakage.
If the tubes are intact, you'll then need to check the voltages from the backlight inverter.
If voltages are missing, consider replacing the backlight inverter.
{If it is on a separate board from the rest of the set.}
Otherwise...
Start testing the driver transistors, and checking for popped Capacitors.
Burned or open Resistors, and Diodes.
Note: Most of the components are going to be SMD type.
So, if your at this point, your probably going too need to find a schematic.
Just to know what some of the SMD components are.

Good Luck!


Signed: Janitor Tzap

User avatar
haklesup
Posts: 3007
Joined: Thu Aug 01, 2002 1:01 am
Location: San Jose CA
Contact:

Re: Dropped flat screen

Post by haklesup » Tue Sep 20, 2011 1:31 pm

If the CFL lamps themselves are not broken then most drop caused faulures are the result of dislodged connectors, board to board connections and or larger components being pulled from the PCB or assembly by momentum. Check all the interconnections and the solder joints of the larger components.

From your initial observations, a fault in the backlight either the lamp or the CFL driver board are the right places to look.

User avatar
Externet
Posts: 1844
Joined: Fri Feb 01, 2002 1:01 am
Location: Mideast USA
Contact:

Re: Dropped flat screen

Post by Externet » Tue Sep 20, 2011 6:35 pm

If its weight allows, shake/spin the TV. If backlight bulbs are broken, you should hear glass pieces dancing inside.
Some backlight lamp assemblies can be removed by sliding them out of their channels.

Measure voltages at all INPUT pins of the inverter board, against chassis ground; come back with findings.
Miguel
- Abolish the deciBel ! -

Post Reply

Who is online

Users browsing this forum: No registered users and 7 guests