Was working fine until recently, the back light seems to be shutting
off. After turning on the tv, the screen will light up for about 1-2
seconds then it will shut off and become black, but the tv remains on
and working otherwise. Shining a flashlight on the screen indicates
the picture is there. Audio is OK.
Anyone know if this is a systemic problem with this TV? If so, is
there a well-known fix?

Any other thoughts about what could be the root problem?
So for this model, where is a good place to get replacement parts?
(e.g. inverter board, lamps)

Thanks
-John

jjh wrote:
Was working fine until recently, the back light seems to be shutting
off. After turning on the tv, the screen will light up for about 1-2
seconds then it will shut off and become black, but the tv remains on
and working otherwise. Shining a flashlight on the screen indicates
the picture is there. Audio is OK.
Anyone know if this is a systemic problem with this TV? If so, is
there a well-known fix?

Any other thoughts about what could be the root problem?
So for this model, where is a good place to get replacement parts?
(e.g. inverter board, lamps)

Thanks
-John

Not an LED type I assume. Seems to be a common fault. The back light electronic
usually consists of a number of identical circuits. The controller checks the
current of all of them.
If only one is out of range it will shut down.

Check the resistance of the transformers. Chances are one is out.
Be careful and make sure there is no high voltage left when working on the
inverter board.

Tony

mine turned out to be 2 broken ccfl lamps. Like Tony said, it detected low
current on this circuit and shut it down. I ordered 2 new lamps.
Roy

On Thu, 17 Dec 2009 08:09:20 -0800 (PST), jjh
wrote:

Was working fine until recently, the back light seems to be shutting
off. After turning on the tv, the screen will light up for about 1-2
seconds then it will shut off and become black, but the tv remains on
and working otherwise. Shining a flashlight on the screen indicates
the picture is there. Audio is OK.
Anyone know if this is a systemic problem with this TV? If so, is
there a well-known fix?

Any other thoughts about what could be the root problem?
So for this model, where is a good place to get replacement parts?
(e.g. inverter board, lamps)

Thanks
-John
Common failures of the backlight system include bad capacitors, aging
or broken CCFLs, wiring problems (bad solder joints, arcing) to the
CCFLs, bad transformer, or a fault in the CCFL monitoring circuit.

If you have a DMM and steady nerves, it is possible to isolate the
problem. The first step requires opening the TV and locating the
power supply and the inverter. Look for bulging capacitors in the
power supply and the inverter.

Next look at the leads from the inverter to the CCFLs (backlights).
Usually the wires are in pairs. If the wires in the pairs are of
different diameters the smaller diameter wire is the return line.
Measure the AC voltage on each return line as the backlights are
operating. (Yes, you only have a few seconds). Normally each wire
will have the same voltage; you are looking for the one that is
noticably different than the others.

The other step may require removing the inverter from the TV. With it
unplugged from AC power measure the resistance between the leads of
the transformers. Again, you are looking for the thransformer that is
significantly different than the rest.

PlainBill

Thank you, and a follow-up question*

Next look at the leads from the inverter to the CCFLs (backlights).
Usually the wires are in pairs. *If the wires in the pairs are of
different diameters the smaller diameter wire is the return line.
Measure the AC voltage on each return line as the backlights are
operating. *(Yes, you only have a few seconds). *Normally each wire
will have the same voltage; you are looking for the one that is
noticably different than the others.


Measure across the return line to what? Is there a well marked
grounding point on the board? Or should I just measure across the two
wires to see what voltage the lamp is getting, and look for one with a
significant difference among the others?

Thanks you all for your pointers...

If the CCFL's are bad, where is a good place to buy replacements at a
reasonable cost?

TIA,
John

On Mon, 21 Dec 2009 08:13:40 -0800 (PST), jjh
wrote:

Thank you, and a follow-up question*

Next look at the leads from the inverter to the CCFLs (backlights).
Usually the wires are in pairs. *If the wires in the pairs are of
different diameters the smaller diameter wire is the return line.
Measure the AC voltage on each return line as the backlights are
operating. *(Yes, you only have a few seconds). *Normally each wire
will have the same voltage; you are looking for the one that is
noticably different than the others.


Measure across the return line to what? Is there a well marked
grounding point on the board? Or should I just measure across the two
wires to see what voltage the lamp is getting, and look for one with a
significant difference among the others?

Thanks you all for your pointers...

If the CCFL's are bad, where is a good place to buy replacements at a
reasonable cost?

TIA,
John
DO NOT measure across the CCFLs. Unless you have a DMM designed for
2KV AC this could destroy your DMM. Measure from the return line to
ground. The metal chassis is a good point. Quite often the circuit
boards will have a small grounding tab under one screw. I use the
head of that screw as a ground point.

Google 'CCFL backlight', you will find several vendors who manufacture
CCFLs in a variety of lengths and diameters. Based on my experience,
the CCFL is one of the least likely parts to fail. Transformers and
wires are more likely causes of the 'two seconds to black' symptom.

PlainBill