LCD TV Backlight Repair From CCFL to LED

by fbelmonte

37K15016

Intro: LCD TV Backlight Repair From CCFL to LED

While reading and browsing instructables on Arduinio CNC and related topics, I came across with one instructables that caught my attention. This is replacing the "LED Backlight for An LCD Monitor or Television" with LED Strip. I have an old defective LCD 13" TV around for ten years. I already discarded the casing, what is left is the metal part that support the Logic Board, Power Supply , Inverter and LCD. I did not trash because I was hoping to get parts for future projects. The problem with this LCD TV is the 2 second auto shutdown, during that time, I dis assembled the TV hoping to repair. I was able to isolate that when, the inverter/LCD is removed, I can hear sound of the TV, meaning it is working without the display. But I do not know how to repair that part, and so it went to stock area for a long time.

https://www.instructables.com/id/LED-Backlight-for-Your-LCD-Monitor-or-Television/

Until recently after reading that article, I tried to repair the TV. Able to isolate the Inverter and removed the CCFL to test, and lo and behold, the other side of 4 CCFL inverter is defective. The mosfets are shorted. I tried to use only the other side by cutting traces and isolate the shorted parts, but still the TV auto shutdown. Putting a flashlight into the screen will show that it is working. My option is to buy universal inverter since both CCFL still working, but I like better the LED strip option since this is cheaper and safer. I created relay switch so that the LED strip is off when TV is off also. I know this is not the best option, but for this, works perfectly and served my purpose. This is also very cheap and quick repair. I spent around $4 only on this.

Parts :
LED White Strips - 2 ( 10 inches each )

LED Red - 1 ( For relay indicator )

12V Relay - 1 ( Normally open from an old TV board )

BC547 (NPN) - 1 ( For relay switch )

Diode (Rectifier) - 1 ( For relay protection )

Resistor 10K - 1

Resistor 1 K - 2

Assorted Wires - For connection

Breadboard - 1 ( For the relay switch circuit )

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Warning : Please always work safely and respect any power source even if it is low voltage. This project will require working with TV power supply and high voltage Inverter. I am not responsible for any harm or damage to anything it may cause to anyone that will try this instructables. Remember to remove power and allow time to deplete the power before working on the board.

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STEP 1: Remove CCFL From LCD Screen

Remove the LCD panel from the TV case and extract the CCFL , taking extra careful not to break anything specially the CCFL, LCD board, etc.

STEP 2: Determine the Required Length of LED Strip

Measure the total length of the CCFL and match the LED strip, this strip can cut for every 3 LED. I bought mine from local electronics shop. They sell per 3 LED's.

STEP 3: Connect Wire to LED Strip

Solder the wire on each LED strip, I did this by scratching the self adhesive tape at the back of the strip copper pad. Take note of the polarity and color of the wire to use to ensure that correct potential is provided on each pad.

STEP 4: Build the Relay Switch Circuit

Assemble the relay switch as per schematic and test using any available 12V power supply. I added an LED indicator to know that the relay is activating and triggered with a 5V source. I used my homebrew electronics lab with PC power supply to test the circuit.

STEP 5: Identify Relay Circuit Trigger Pin to Activate When TV Is On

From the inverter connection, locate the pin where it is "Zero" when the TV is off and with any voltage when the TV is on. In this TV I located the one with brown wire. This is using voltmeter and found to be around 3 volts. This is enough to drive the NPN transistor and eventually energize the relay.

STEP 6: Connect the Relay Circuit to the Logic Board

Connect the relay switch Vin to the 3 volts pin, the power of 12V and to ground. Switch on the TV and see if the relay will activate. I removed the connector from the defective inverter and soldered to the relay board.

STEP 7: Re-assemle the LCD Panel With New LED Strip

Assemble the LCD panel together with the LED strip and connect to the relay switch. Ensure to test first prior assembling so that you don't need to re open again when there is problem.

STEP 8: Finally - Connect the New Relay Circuit and LED Strip Together and Enjoy

Replace the inverter board with the relay switch and assemble the TV. Power on and enjoy watching! I enjoyed this activity specially when I saw the TV working again. Have Fun!

14 Comments

ratgod 3 years ago

I did something similar a while back on an old Acer monitor, except I used 3mm white LEDs and hot glued them in a strip, I used a FET to control the LEDs using the front panel power LED as the on indication. It worked except I spaced the LEDs too far apart, the white LED strips weren't as available when I did it, and those were very expensive. I definitely recommend using the strips for the best results. Many thanks for posting this.

imanimani1034 3 years ago

Hello
By making this circuit, I can control the light from the monitor. Or I will only have one fixed backlight

fbelmonte 3 years ago

Hi,

Yes it is possible, the circuit is just a switch using relay.

drew.adc 8 years ago

Nice job. Glad to see somebody used my Instructable. Yours definitely looks better with the bright white LEDs instead of the warm white I used. Good idea with the relay circuit too. I ended up eventually adding a similar circuit using a MOSFET to one of the TVs I did this to, but never got around to adding it to all of them. I was able to use the power line to the led on the front as the input to the MOSFET. It turns them off, but your way guarantees they are completely off.

fbelmonte 8 years ago

Thanks, your instructible did really help and open that idea.

Gelfling6 8 years ago

Comparing from the prices I've seen, How much would the high-output LED strips cost, comparing to a $70 (+/-, in US-$) for the replacement CCFL? I've seen more than my fair share of people on C-List literally giving away their televisions because they either broke or burned out the CCFL, and this might be a more cost effective way to repair for them.

BeachsideHank 8 years ago

This is genius. I have recovered led backlit t.v.'s from the roadside with perfectly good led arrays, in fact I made two illuminated movie posters with them and I now have another find waiting for reuse. It's easy to do and far better than the cfl type.

baecker03 8 years ago

where did the 12 volts come from?

fbelmonte 8 years ago

12 V came from the same source for the inverter, in this case the green wire. This is always present once the unit is connected to power line even if it is off. I located that using the voltmeter and silkscreen on the pcb