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Russell H.
Russell H., Technician
Category: UK Electronics
Satisfied Customers: 10782
Experience:  Repairing devices of UK and European make for over 20 years.
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I have a LG LED Smart TV of model 42LS57OT-ZB with

Customer Question

I have a LG LED Smart TV of model 42LS57OT-ZB with intermittant backlight problems. Sometimes it starts up with no backlight, or partially dimmed, sometimes it fixes itself after a while, some days it works fine, but then on another day it won't work! I can't really detect any pattern in this - unplugging for while doesn't help either, it seems to be random. The TV is out of warrantly so I would like to try and fix it myself if possible. Thanks - Lizzy
Submitted: 1 year ago.
Category: UK Electronics
Expert:  Russell H. replied 1 year ago.

Hi, thank you for contacting My name is Russell. I will do what I can to provide the right answer to your question.

Fixing a TV is a moderately major undertaking, if not in expense, then in care and time and work. I hope you have some tools, and some experience with disassembly of electronic devices (and reassembly doesn't hurt too.) And in many TVs, voltage precautions to avoid burns or electrocution are essential to be observed by anyone servicing the TV.

As for your good, fluent description of the backlight problem... does it ever 'flicker' or 'sputter'? or is it either On or Off, period? if not, then you don't just have a loose or corroded or dirty power connection to it, but rather you may have a defective power supply (which feeds voltage/power to the backlight.) Doubtfully it might be a loose or dirty or corroded connection problem, but sputter and flicker would also result from that at least on occasion.

To put it in a few words: Replacing the power supply, and checking/cleaning/re-seating connections, plus perhaps cleaning dust out first, might be what the problem needs. Let me know more, and ask further queries about details (there is not any extra charge for several queries and answers on the same question.)

Customer: replied 1 year ago.
The screen does flicker, also sometimes some of the backlight is on and some off - so part of the screen is darker than the rest.
I will try opening the TV and cleaning it out, and see if I see any obvious problems. I will unplug it first but are there any capacitors I should be careful of? If it is the power board where can I buy a new one and how easy is it to replace. I don't have soldering/electronics equipment at home, but I can use I have an electronics lab at work which I can use although I would probably not be able to bring the whole TV in.
Customer: replied 1 year ago.
Thanks, Lizzy
Expert:  Russell H. replied 1 year ago.

It sounds as if you are mustering your resources on this matter, bravely.

Be cautioned: a TV may have dangerous voltages inside it. With modern (i.e. flat-screen) types of TV, as opposed to the older 'tube' or 'CRT tube' -type TV, the hazard is somewhat less. But, to prepare a TV for being opened and worked on, you should

A. unplug it from the power / mains / outlet.

B. turn it On with the power switch (even though it is unplugged - this will drain voltages to some extent, that may persist inside it.)

C. leave it that way, unplugged with no power source, but turned On, for at least 2 hours before opening it.

D. Yours is an LED TV. That should be enough - there is no High Voltage section, no 25,000-Volt tube cathode to worry about... just don't use your bare fingers on any capacitor leads! and you should be safe enough after the steps A through C above.

If the backlight is partly On and partly Off, unfortunately (since this is an LED TV) you might have an expensive repair case, one where replacing the TV would be both easier *and* less expensive than repairing it.

The backlight being partly On (and only on part of the screen?? that doesn't sound like a backlight problem. It sounds like a circuitry problem or power transmission problem. Or at worst, the whole display panel is defective, in which case replacing the whole TV would be the better solution...) is not a good sign, but might be owing to defective power supply to it.

(Which might be owing to dirty or corroded connectors...)

So I have to ask, before advising you further:

- How old is the TV, measured from date-of-unboxing ?

- How damp or humid an environment has it been in since it was unboxed and you started using it? damp/humid conditions encourage corrosion.

- As for how dirty or dusty it has gotten... I can't ask meaningfully. When you open it, you'll be able to tell for sure.