How To Repair Lcd Led Power Supply

In the Eastward-book written by Kent Liew – Smart-OLED/LED/LCD Television set Repair Tips – V6, chapter: "Another New Tool to easily to practise the PSU self-test with monitoring feature", guides the reader on how testing can be performed on a PSU without having to connect to the Tv. This examination can confirm the condition of the PSU on whether it is working or it is faulty. With the knowledge gained from Jestine Yong to repair the PSU, I took on this challenge to brainstorm the repair. I decided to repair a faulty Power Supply Unit (PSU) on hand to test the method specified in the Due east-Book.

I perused the web and managed to obtain the circuit diagram for the PSU every bit depicted in Figure A.

This test lath as shown in Effigy B, can be bought from AliExpress.

The PSU tester has built-in load resistors (3 Ten 5W) to simulate connexion to LCD/LED Idiot box, which will switch the PSU on if connected.

Visual checks confirmed that there were no burnt parts. When the PSU was connected to the tester, the tester did not turn on, indicating that the PSU was faulty. Co-ordinate to the label in the PSU output side, the stand-past volt is 5VDC marked as 5VSB (Voltage Standby). This voltage is supplied to the mainboard of the Telly. Without this voltage the TV will not turn on.

Upon checking the primary supply towards Pin 1 and 3 of T401-A (Circle in Ruby), 330V was noted and this proof that this voltage was not boosted. This confirmed that the primary side of the PSU was working well except that the 330 VDC was non additional. This means the PFC circuit was not working due to the missing 12 volt DC (12 VSB) from the main power supply (wait at figure E). When checking the Schottky Bulwark Diodes, information technology came to my attending that the bottom diode (D403 – Circumvolve in Orange) was shorted as displayed in Figure C.

Later on replacing the faulty diode, the fault remained. The ring tester confirmed that the transformer is in working guild (Full lights). This exam was performed at pin ane and 3 of T401-A without applying power to the PSU as shown in Figure D.

Examining the PFC circuit, I realized the PFC IC U201 pin 8 (VCC) had no voltage supply every bit shown in Figure E.

Following the VCC_PFC supply line, the VCC_PFC supply to U201 as portrayed in Figure F, was noted that it was coming from the below circuit:

The Drain (D) pin receiving 330 VDC steps down the voltage through built in regulation circuit (five.75 volt) and this ways this IC does not need a start upwardly resistor. This is depicted in Effigy M.

Suspecting a faulty IC U401 (no switching) -figure H, I replaced the faulty LNK6767 with a LNK6777V every bit information technology was the direct substitute for LNK6767 available for replacement in the market. This replacement IC resulted in the 12 volt DC output (12 VSB) return.

However, in that location was still no standby voltage of 5VSB. Upon tracing the voltage lines of the DC-to-DC converting circuit, information technology came to my knowledge that the 5VSB is produced by IC U501 (MP1584EN), a loftier frequency stride-down switching regulator with an integrated internal high-side loftier voltage ability MOSFET. This tin can be observed in Effigy I as shown below.

When probing, I realized that Pin 7 of U501 was receiving the 12VSB merely there was no voltage output at pin one. I proceeded to supervene upon the U501 which resulted in the render of the 5VSB.

Finally, I tested the repaired board with load using the PSU tester as shown in Figure I. Connecting the repaired lath to the tester showed that the PSU is fully functional.

With the guidance of Jestine Yong, I was able to complete this repair within a week, a record timing for me! I promise it was an informative read for you. Thank you for reading thus far. Exercise try this approach should yous see a power supply unit without a Boob tube for testing.

This commodity was prepared for you by Michael Selvam from Singapore, a 57 twelvemonth old zealous electronic enthusiast. Every bit a passionate electronic repair hobbyist, he tinkers with home amusement systems and any faulty electronic equipment he gets his hands on. He obtained his knowledge to repair by reading books and took upwardly the electronic courses I conducted. At present, he is employed as a Cluster Manager (Holding Management) with CapitaLand and does his repair whenever time permits.

From Jestine: For your information, Michael was my training student and you can check out his training photo Here .

Please give a back up by clicking  on the social buttons below. Your feedback on the post is welcome. Please leave it in the comments.

P.South-If you enjoyed reading this,click here to subscribe to my blog (free subscription).That way, you'll never miss a post. You can also forward this website link to your friends and colleagues-thanks!

You may bank check on his previous repair article below:

https://jestineyong.com/repair-of-philips-led-smart-tv-55pft6100-98/

Likes(85) Dislikes(0)

Source: https://jestineyong.com/repair-and-test-of-led-tv-power-supply-board-without-connecting-to-a-tv/

Posted by: lathamwormse.blogspot.com

Share this post