LCD Repair Questions

[cloudsloth]

Hello, first post over here.

I recently picked up several nice LCD monitors from a recycling event. They all have similar issues of powering on for several seconds and then flickering out. One of them flicks on for about 1/4th of a second, another does more flickering and takes 1-6 seconds to turn off, and the third stays on until anything moves on screen than flickers to darkness.

I've read a lot about capacitor replacement, have basically seen two suggestions: replace the bulgy leaky ones, or replace them all. Anyone have experience in diagnosing a capacitor problem when none are bulgy/leaky? Are there any other common dead parts to be replaced for flicker issues like I'm having?

And finally, my research suggests that the UF value is critical, the voltage value is a minimum and should be limited to a variance of ~30%, and that the temperature value is not paid much attention too. Does anyone here disagree?

Thanks in advance,

Cosmo

 

[ram1009]

Hello, first post over here.

I recently picked up several nice LCD monitors from a recycling event. They all have similar issues of powering on for several seconds and then flickering out. One of them flicks on for about 1/4th of a second, another does more flickering and takes 1-6 seconds to turn off, and the third stays on until anything moves on screen than flickers to darkness.

I've read a lot about capacitor replacement, have basically seen two suggestions: replace the bulgy leaky ones, or replace them all. Anyone have experience in diagnosing a capacitor problem when none are bulgy/leaky? Are there any other common dead parts to be replaced for flicker issues like I'm having?

And finally, my research suggests that the UF value is critical, the voltage value is a minimum and should be limited to a variance of ~30%, and that the temperature value is not paid much attention too. Does anyone here disagree?

Thanks in advance,

Cosmo

I hope you're doing this for reasons other than profit. Re-working circuit boards is tedious and risky even for experienced techs with professional equipment. Many times the board will be damaged by the repair process without your knowledge until reassembly. Most of the time faulty equipment can be replaced with new equipment for less than the cost of repair. That's why nobody does it. The capacitors you're talking about are called "electrolytics" and your info is reasonably correct although I would try very hard for exact values. One thing to remember about electrolytic caps is to always observe the proper polarity. Good luck.

 

[bobalazs]

Those errors are to be contributed to bad inverters, not capacitors.
If you do measure them out, though, you might have to change that also though.

 

[pjmelect]

A common problem in LCD monitor repairs is that the external brick power supply becomes faulty. This is invariably due to the capacitors in it going faulty giving the symptoms that you have described. Normally it is obvious by looking at the capacitors which ones are faulty because they have become leaky or bulgy. Sometimes the capacitors become bulgy at the bottom of the case which is not easy to see, check for capacitors not standing up straight. Other times the capacitors look perfectly normal but have reduced in capacitance or more commonly have increased in ESR. An in circuit ESR tester is what I use to test capacitors in this case. As there are not that many capacitors in the power supply you could just replace every one and I recommend that you replace them with 105 degrees ones.

The capacitance value is not that critical if the capacitance is higher (not lower) than the rated value, the voltage is also not critical if the voltage is higher (not lower) and that you can fit it in the space provided. If you want the repair to last put in higher temperature ones.

 

[Guest]

Also one should never limit their trouble shooting to caps alone believe you me when it comes to S M P S even one resistor that has lost tolerance is enough to affect the performance of the power supply

 

[MMclachlan]

One optimistic voice over here!
I picked up a Dell 15" a while ago which had a backlight problem similar to the first you describe - powering on for a short while then the backlight going off. This did indeed turn out to be a single bulged capacitor on the inverter board. Monitor cost me about £6.50 including doing the repair.

 

[rickhan]

There was a massive number of sub-par capacitors used in many monitors and TVs a number of years ago. I found 5 bulging ones on my Samsung monitor power supply board. The board is single layer, and it was trivial to replace the capacitors. Works like new.