Hey all,

I found an LED TV and decided to try and fix it. It powers on and there's sound, and when I light a flashlight on it there's an image. I figured the backlight is broken so I measured the output to the LED driver with a dvm and it gives me an unstable reading (12 V, 10 V, 8V, etc.. down to 0V) in a cyclic manner.
Any idea where to start looking? (all capacitors look ok). PCB is EAX64905301

Thanks

 

Is this really an LCD TV with a duff backlight?
If so, the first thing to do is to establish what kind of backlight it uses.

 

Is this really an LCD TV with a duff backlight?
If so, the first thing to do is to establish what kind of backlight it uses.

LED not LCD

 

You most likely have a few bad LEDs. You're going to have to crack open the panel.

 

You most likely have a few bad LEDs. You're going to have to crack open the panel.

I measured the voltages with the LEDs disconnected. My first guess is that the power supply board is faulty...

 

I measured the voltages with the LEDs disconnected. My first guess is that the power supply board is faulty...

You can't get the voltage you want with the LEDs disconnected. The driver will interpet this as "LEDs OPEN" and flag a fault.

You have bad LEDs. You're going to have to crack open the panel.

 

LED not LCD

Just for the record: http://www.cnet.com/uk/news/led-lcd-backlights-explained/

 

You can't get the voltage you want with the LEDs disconnected. The driver will interpet this as "LEDs OPEN" and flag a fault.

You have bad LEDs. You're going to have to crack open the panel.

When the LEDs are connected the blink every few minutes, with correlation to voltage peaks (what I described earlier). Does it make sense that the LEDs are faulty? The voltage measurements are

Just for the record: http://www.cnet.com/uk/news/led-lcd-backlights-explained/

I know, but since we deal with backlighting here, it is important to not that it's an LED TV (uses LEDs for backlighting..)

 

Note the section at the start of this video - they can help with your particular symptoms.
https://www.youtube.com/watch?annot...&feature=iv&src_vid=8HG7efTMj78&v=xUzCLgoSPGM

 

When the LEDs are connected the blink every few minutes, with correlation to voltage peaks (what I described earlier). Does it make sense that the LEDs are faulty?

All this depends on the TV's software. If the LED driver(s) sense a fault, they will shut down. The main software may wait for a few minutes, then try to reset everything, then LEDs on, fault detected, shutdown all over again, ad infinitum.

 

What is the make and model of the TV?
Can you post some nice clear picture of the back of the set?
Have you checked all the voltages from the power supply? Post your results please.
Capacitors can be bad even when they look good. Do you have an ESR tester?

 

I had the same problem - unstable backlight reading on power board. All LED strips are OK (tested with 9V batteries) but contact between two LED strips was damaged. I repaired contact with piece of wire and TV works again!