LG55UH615T Tripping after backlight replacement. Uses LGP55LIU-16CH2 power supply

[alltvrepairs]

Hi,

This TV uses 2 bottom edge LED strips. 1 was faulty but replaced both. However I have still noticed that the RHS of the TV switches on and then TV starts to recycle power getting to the LG logo and start over. If I disconnect the RHS LED strip will work with half screen lit. I have swapped LEDs and same problem.

The power supply uses MAP3516 chip. Have replaced it twice, Checked all components as greatly suggested in this post https://www.badcaps.net/forum/troubl...-redstanby-led

Changed both Mosfets 5N40 just in case, checked both 4R7 SMDs out of place and all surrounding components ( excluding value smd caps but no shorts across).

I have tried to reduce the Backlight current by fitting 4R7 (2W) R808 in series to the existing 3R3 R804 and TV set stayed On. Tested for 24hrs straight on Sports mode. (With the added Series resistors smaller than 4R7 still trips). The LED voltage measures 164Vdc on both strips. The picture is still good although reduced Backlight and tested in all Picture Modes. However I know that something is not 100% right.

A datasheet for MAP3516 will help a lot.!

Thanks guys!

[nomoresonys]

That mod you did will make the leds last a lot longer, it kind of looks like maybe there's a faulty led on that side of the new led strip.

[Diah]

LED current limit R are at the downside of the boards .. SMD R did you take look there and tested them if one Open

[nomoresonys]

Good suggestion Diah, it probably is a bad resistor/s there, one poster said his resistors tested within specs but changed them anyway and solved the flicker.

[nomoresonys]

I didn't pay attention to what kind of resistor mod was done, just assumed it was correct.

[alltvrepairs]

That mod you did will make the leds last a lot longer, it kind of looks like maybe there's a faulty led on that side of the new led strip.

The current limit of the RHS LED circuit is much more sensitive. I have swapped LED strips to confirm that. Tested for another 24hrs straight and so far all is well. Have just received a new MAP3516 from another supplier and am tempted to swap again just in case my chinese replacement version was out of tolerance

[alltvrepairs]

LED current limit R are at the downside of the boards .. SMD R did you take look there and tested them if one Open

Hi tks for your reply, Not sure which R number you are referring as I wasn't able to find the datasheet of the chip or circuit for this board however there are 2 4R7 SMDs ( R822) that I have removed from place and swapped positions but same problem that is RHS requires reducing BL and LHS all fine.

[Diah]

upload clear photo of the BL circuit downside of Power boards you will see the SMD R

[alltvrepairs]

upload clear photo of the BL circuit downside of Power boards you will see the SMD R

Found this handy on this forum. Can you help with R?
Tks

[lotas]

Hi,


I have tried to reduce the Backlight current by fitting 4R7 (2W) R808 in series to the existing 3R3 R804
Thanks guys!

You have reduced this very much, you need to remove 3.3 Ohm and put 4.7 Ohm.

[Diah]

Found this handy on this forum. Can you help with R?
Tks

this is mode to reduce the currents on LED strips. you should not follow this right now.... with every things as original you should trouble shoot this circuit you show. to have both strips lighting on... now you have only one.... after you have normal BL come on... then you can modified this mode to bring the current down..
so every things put as normal and test all SMD R if there are one open or changed value to high

[vinceroger69]

The current limit of the RHS LED circuit is much more sensitive. I have swapped LED strips to confirm that. Tested for another 24hrs straight and so far all is well. Have just received a new MAP3516 from another supplier and am tempted to swap again just in case my chinese replacement version was out of tolerance

is the tv working ok now i see you have tested it for 24hrs

[alltvrepairs]

Hi,
I can confidently say that the TV has been fixed after latest update. I have replaced SMD 4R7 R828 with 3R3. Most probably the new LED bars fitted have slightly different specs than the originals. Also I have replaced both current limiting resistors R808, R804 from 3R3 (2W) to 4R7 (2W). With Backlights set at 100% I have a terminal LED voltages of set 1 169V and set 2 169.3V

[nomoresonys]

Nice work, looks like a good picture on that tv.