LG 50UH5530 LED TV suddenly won't power up

[kr00]

The TV was working properly, then after powering off for about 2 hours, the TV will not power up. The standby light is on, and solid as usual. When powering on, the screen will light up for about 1 second, then shuts off, and the standby light comes back on. When attempting to power on a second time, the screen does not flash, but the standby light flashes 3 times, then goes back to solid. Unplugging the TV for about 30 seconds will allow the replication of these events exactly.

When testing the Power board, the standby output lead shows zero voltage rounded to a hundredth. All capacitors look normal, and all fuses are good. The power board model is L5L01F.

Is there any hope of repairing this power board?

[budm]

Re: LG 50UH5530 LED TV suddenly won't power up

Please attach good clear pictures of the whole backside of the TV showing all the boards, and good clear straight shots of the whole power supply board so we can see what we are dealing with.

[kr00]

Re: LG 50UH5530 LED TV suddenly won't power up

I included a closer view of the power board halved in two separate photos in addition to a photo depicting the entire board.

[Diah]

Re: LG 50UH5530 LED TV suddenly won't power up

screen will light up for about 1 second mean you have ONE LED shorted at the back light

[budm]

Re: LG 50UH5530 LED TV suddenly won't power up

You need steadier hand when taking pictures, the pictures are blurry.
Any how, lest start by check the Voltages on the black connector, all connectors must be back in place, of the power supply board to see if the power supply Voltages or control Voltages are still present or not.
The connector pins are arranged in EVEN and ODD column as shown on the chart printed on the circuit board, the ODD column you can make the measurement by probing the pins on the exposed pins on the top side of the board, for the EVEN number pins you will need skinny probe to probe from the connector wire entrance side.
You will leave the Black probe of the meter on the chassis, then read probe on each pin.
You MUST report the readings when the power switch is activated, do not worry what condition of the TV is in after the power switch is activated.

Odd column pins:
Pin 1 STB = xxx V
Pin 3 GND = xxx V
Pin 5 13.2V = xxx V
Pin 7 13.2v = xxx V
Pin 9 .................
so on and on for other pins.
https://www.badcaps.net/forum/attach...2&d=1596323041
You do have and know how to use Digital meter, correct?

The problem can be bad LED also, we can check the Voltages on the LED connector next. The set has 3 LED strings.

[kr00]

Re: LG 50UH5530 LED TV suddenly won't power up

I attached a more clear photo near the main board connector. This one seems less blurry. The values of the 12 pins are below. All 13.2 V pins gave values among the range listed by each.

ODD
ENA => 0 V
GND => 0 V
13.2V => 7.4 -10.11 V
13.2V => 7.4 - 10.11 V
GND => 0 V
STB => 0 V

EVEN
ADJ => 0 V
GND => 0 V
13.2V => 9.5 - 10.7 V
13.2V => 9.5 - 10.7 V
13.2V => 9.5 - 10.7 V
NC => 0 V

After testing this, I disconnected the main board again, and values remained the same on all pins. I also heard a distinct "ticking" sound about every 1.5 seconds after attempting to power on which had not been present before.

[budm]

Re: LG 50UH5530 LED TV suddenly won't power up

I attached a more clear photo near the main board connector. This one seems less blurry. The values of the 12 pins are below. All 13.2 V pins gave values among the range listed by each.

ODD
ENA => 0 V
GND => 0 V
13.2V => 7.4 -10.11 V
13.2V => 7.4 - 10.11 V
GND => 0 V
STB => 0 V

EVEN
ADJ => 0 V
GND => 0 V
13.2V => 9.5 - 10.7 V
13.2V => 9.5 - 10.7 V
13.2V => 9.5 - 10.7 V
NC => 0 V

After testing this, I disconnected the main board again, and values remained the same on all pins. I also heard a distinct "ticking" sound about every 1.5 seconds after attempting to power on which had not been present before.

So those readings are done without the cable between power supply board and the main board connected?
What do Voltages on those same pins if you do NOT have LED connector in place also?
Ticking sound from power supply board?
BTW, I am still having hard time reading the P/N as printed on the bar code and on the board so I can locate good clear pictures of the whole top and bottom side of the board, i need then to be really clear so I can trace out the schematic.
Can you provide me with good clear pictures of the whole top and bottom side of the board?

[kr00]

Re: LG 50UH5530 LED TV suddenly won't power up

Those readings were taken with all connectors in place. After testing, I unplugged the TV, then disconnected the main board connector, and tested all pins again. When testing with the main board disconnected, the 13.2V pins gave a reading of about 9.9V, and all other pins remained the same. Getting 0V on the STB pin seems odd.

After removing the LED connector, the pins did not appear to change voltage at all.

The ticking sound is coming from the power board.

I took one close up photo of the bar code number.

When you say "top and bottom" of the board, do you mean the under side of the board which lies near the TV chassis when referring to the "bottom" of the board?

[budm]

Re: LG 50UH5530 LED TV suddenly won't power up

Those readings were taken with all connectors in place. After testing, I unplugged the TV, then disconnected the main board connector, and tested all pins again. When testing with the main board disconnected, the 13.2V pins gave a reading of about 9.9V, and all other pins remained the same. Getting 0V on the STB pin seems odd.

After removing the LED connector, the pins did not appear to change voltage at all.

The ticking sound is coming from the power board.

I took one close up photo of the bar code number.

When you say "top and bottom" of the board, do you mean the under side of the board which lies near the TV chassis when referring to the "bottom" of the board?

1) In standby, the 13.2V power supply may only put out about 10V, but when it is turned on then it will jump up to 13.2V. So right now is it sitting steady at 9.9V?

2) STB pin is the PS-ON pin, it receive the on command from main board.

3) So is the power supply still ticking when nothing connected to the board but just the AC power?

4) We will force on the power supply (nothing connect to the board except the AC power) by using 1 ~ 2K resistor between STB pin and 13.2V pin, you should see steady 13.2V at 13.2V pin.

5) The pictures I need are the straight shots of whole top side of the circuit board and then the whole bottom side of the board where copper traces and the surface mounted components are.

6) Do you have LED tester? This TV uses 3 LED strings.

[kr00]

Re: LG 50UH5530 LED TV suddenly won't power up

1) In standby, the 13.2V power supply may only put out about 10V, but when it is turned on then it will jump up to 13.2V. So right now is it sitting steady at 9.9V?

2) STB pin is the PS-ON pin, it receive the on command from main board.

3) So is the power supply still ticking when nothing connected to the board but just the AC power?

4) We will force on the power supply (nothing connect to the board except the AC power) by using 1 ~ 2K resistor between STB pin and 13.2V pin, you should see steady 13.2V at 13.2V pin.

5) The pictures I need are the straight shots of whole top side of the circuit board and then the whole bottom side of the board where copper traces and the surface mounted components are.

6) Do you have LED tester? This TV uses 3 LED strings.

1) In standby, the 13.2V pins have been sitting steady at 9.9V.

3) In the last power up, I heard no ticking sound coming from the power board as before.

4) I do not know how to perform what you are requesting in step 4.

5) I will upload pictures of the face and backside of the board as soon as I am able. It seems as though the pictures previously have not been of sufficient quality, and so, I am afraid that the future pictures will be no better.

6) I do not have an LED tester.

[budm]

Re: LG 50UH5530 LED TV suddenly won't power up

1) In standby, the 13.2V pins have been sitting steady at 9.9V.

3) In the last power up, I heard no ticking sound coming from the power board as before.

4) I do not know how to perform what you are requesting in step 4.

5) I will upload pictures of the face and backside of the board as soon as I am able. It seems as though the pictures previously have not been of sufficient quality, and so, I am afraid that the future pictures will be no better.

6) I do not have an LED tester.

1) That 9.9V in standby is normal then, it is enough to keep the main board alive..

[kr00]

Re: LG 50UH5530 LED TV suddenly won't power up

However, in standby, the STB pin gives 0V. I was under the impression that it should be around 3.3V or 5V, depending on the board. Does this mean the issue is with the power board and that it simply needs to be replaced?

[neilc6]

Re: LG 50UH5530 LED TV suddenly won't power up

The STB pin is a logic signal from the main board to the power supply to turn the power supply on (sometimes labelled PS-ON). It should go high when the TV is turned on. By using a pull up resistor in step 4, this will force the power supply on with the main board not connected so you can test the output voltage.

[budm]

Re: LG 50UH5530 LED TV suddenly won't power up

However, in standby, the STB pin gives 0V. I was under the impression that it should be around 3.3V or 5V, depending on the board. Does this mean the issue is with the power board and that it simply needs to be replaced?

See my post 9 about STB pin.

[kr00]

Re: LG 50UH5530 LED TV suddenly won't power up

See my post 9 about STB pin.

I apologize for my ignorance, but I am still unclear on what I need to do to "force on" the power supply with the main board disconnected.

[kr00]

Re: LG 50UH5530 LED TV suddenly won't power up

1) In standby, the 13.2V power supply may only put out about 10V, but when it is turned on then it will jump up to 13.2V. So right now is it sitting steady at 9.9V?

2) STB pin is the PS-ON pin, it receive the on command from main board.

3) So is the power supply still ticking when nothing connected to the board but just the AC power?

4) We will force on the power supply (nothing connect to the board except the AC power) by using 1 ~ 2K resistor between STB pin and 13.2V pin, you should see steady 13.2V at 13.2V pin.

5) The pictures I need are the straight shots of whole top side of the circuit board and then the whole bottom side of the board where copper traces and the surface mounted components are.

6) Do you have LED tester? This TV uses 3 LED strings.

After connecting the STB and 13.2 pin with all connections to the power board unlogged except the the AC power, every 13.2V pin reads 12.96V.

[kr00]

Re: LG 50UH5530 LED TV suddenly won't power up

After more attempts of trying to find fault with the power board or main board, I decided to dismantle the TV further to test the LED strips. This seemed to be a possible point of failure since the screen would power up for less than a second then go black.

Upon testing the strips, one LED strip would light up then fade out completely. I replaced this strip, and now the TV is working properly again.

Thanks for the assistance.

[AFVet]

Re: LG 50UH5530 LED TV suddenly won't power up

Guys,
I have same problem as KR00, I tested all LED strips, they seemed to test all good with LED tester. After putting the TV back together, it came up once and I hit the power off button, which went to the red standby light, after attempting to power back up to verify, it went back into fault and blinking two red lights. I went down the same rabbit hole thinking the STB should be 3-5 Volts, now after reading your responses, I see it was in vain. All LED strips lit up, do you think I still have and LED problem?

[nomoresonys]

Re: LG 50UH5530 LED TV suddenly won't power up

yep, most cases of one flash then off, means a backlight issue.

[AFVet]

Re: LG 50UH5530 LED TV suddenly won't power up

Not sure what brought it back on line, checked PS capacitors and transistors, rechecked backlights. All tested good. put it all back together and the darn thing started working. Not sure what it was maybe bad solder joint, or just the josling caused it to come back online. We'll see how long it lasts. Bein on all day, turned on and off with remote just fine.