# pc lcd Monitor Shuts off



## alazghari (Jan 31, 2010)

Helloo Everyone..
I am kinda new to the field of electronics, however am still having certain obstacles understanding several lcd problems..
One of these problems is having the pc lcd monitor shutting off after a few sconds to minutes, I then have to click on the standby button to make it work, but,even so, the monitor goes off again..
This problem do happen a lot on LG and Samsung Lcd monitors.

So, I just want to ask if that problem can be solved by replacing any of the capacitors or transistors!
If so, I would be greatful..
Thanx in advance.


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## Done_Fishin (Oct 10, 2006)

replace any capacitors that look as they they are malformed. If none look malformed try replacing any in the inverter feed to the CCFL. Then work back.

Shine a lamp sideways on at the monitor (or look carefully when no cable is attached) to see if you can see the warning message that cable is not attached when the screen has gone dark. I am assuming that the green power LED stays alight. If it goes off then the Monitor is shut down.
In this case replace power supply capacitors. If that doesn't work then try the capacitors on the smps controller. Look for a transistor or SMD IC TL431A. They sometimes fail and give a wrong reference voltage (2,5V). It will be close to an opto-coupler by the transformer.


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## alazghari (Jan 31, 2010)

Thank you for your rich reply..
Tomorrow I will follow your steps and see what happens.
I've already checked the capacitors, they just look fine and new, and there is no sign of failure or malfunctioning..
So, am doubting that this has to do with the transistor..

The screen works fine for the first 6 to 10 minutes, after that, I can see an instant decrease in the level of lighting before it immediately turns to a black screen.. I click on Standby Button, the screen appears again, but this time less time before it shuts off..
If I leave the screen off for some while, it works 6 to 10 minutes when I turn it on, as I said before, then ooooops!

so, my guess is that a component fail to do its job in the circuit after it reaches a degree of heat or something..

I will report to you back what I got with your suggestions.
Thanks again..


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## Done_Fishin (Oct 10, 2006)

I suggest you start with capacitors. They don't always look stressed but replacement cures problems. The problems are not always the same.


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## alazghari (Jan 31, 2010)

I'm back now after I have been searching for new capacitors in stores.
so I bought them and replaced the old ones on the power supply board of the lcd.
but the problem presists..
so, you suggest that I move on to replace the transistor!


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## Done_Fishin (Oct 10, 2006)

TL431A Voltage reference but please check my previous post and answer the questions. Without confirmation of facts I could be steering you a totally wrong course.



Done_Fishin said:


> replace any capacitors that look as they they are malformed. If none look malformed try replacing any in the inverter feed to the CCFL. Then work back.
> 
> Shine a lamp sideways on at the monitor (or look carefully when no cable is attached) to see if you can see the warning message that cable is not attached when the screen has gone dark.
> 
> ...


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## alazghari (Jan 31, 2010)

Thanks for replying again..
Well.. When the screen becomes black, the power led stays on.
and before I know the screen is going black, I can see an instant decrease in brightness for about 1 second.


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## Done_Fishin (Oct 10, 2006)

power led remains on means that your power supply is probably working OK.

you get some backlight (which fails), means that your problem is most likely backlight/inverter/PSU.

you will have to experiment with swapping CCFL, inline capacitor at CCFL, IC that controls inverter circuit.

Normally and in most cases the culprit is a power supply capacitor which you say has been replaced.

Unfortunately that means you will need to experiment to find the real culprit.


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## amerillove (Feb 9, 2010)

Try to look for a transistor or SMD IC TL431A. They sometimes fail and give a wrong reference voltage (2,5V).


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## rb0746 (Feb 18, 2010)

It would really help if you would post some pics of the boards fronts and back


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