Evening All,
Having some trouble with an LG TV that failed a couple of months outside the warranty period.
Link to the model here:- http://www.lg.com/uk/tvs/lg-49UB850V
Before I start, I should say that although I've fixed a few simple things in the past, I know nothing about TVs other than what I've picked up trying to troubleshoot this and I'm not the sharpest when it comes to electronics or circuit diagrams so please bear with me if something simple goes way over my head
I have looked through as many threads, Youtube videos and repair guides as I can find but can't see any that seem to be the exact same issue. This thing is driving me up the wall so would really appreciate any input at all.
The Problem:-
Tried to turn the set on as normal one day and found it essentially dead. No Video. No Audio. No Backlight. No steady LED standby light on front of TV.
On pressing the standby button on the remote (or the joystick on the back of the TV), the standby LED blinks on-off 3-times and then stays off permanently until you disconnect & reconnect the power from the mains.
On the power board, there is a debug LED (LD701) which blinks amber on-off 5 times, repeatedly. This happens around 30 seconds after an attempt to turn the set on using the standby button.
What I've Tried:-
Firstly, I managed to find an LG service manual for a similar model that looks close enough for the instructions to be relevant. PDF attached.
Tried turning the set off from the mains for 12 hours and back on as sometimes suggested by LG support. No difference.
Checked the power board visually for any bad capacitors/resistors but can't see anything that looks bulged/burnt/damaged. I realise something could still have failed without any obvious signs but my soldering isn't great and I didn't think taking the big caps off the board to test them outside the circuit was a good idea before I'd checked the voltages.
Checked all the voltages on the 28-pin connector that joins the main board to the logic board as suggested by the service manual. Readings:-
3.5v = 3.54v (Standby & Power On)
12v = 11.79v (Power On)
24v = 23.7v (Power On)
SLCK, SW & YSYNC = All 1v (Power On)
Also spotted a row of test points for what I'm guessing are the LED circuits at the top of the PSU board so tested them as well in case anything jumped out.
P210 = 48.8v
EL85 = 0.8v
EL86 = 0.82v
EL87 = 0.8v
EL82 = 0.82v
EL83 = 0.8v
EL84 = 0.82v
EL79 = 0.76v
EL80 = 0.81v
EL81 = 0.85v
EL78 = 0.78v
EL77 = 0.78v
EL76 = 0.8v
Not quite sure what values these should be at so these readings didn't really tell me much.
I tried the flashlight test to see if I could pick up any image at all on the screen. Saw nothing - completely black.
Tried the hairdryer trick (Don't have a heat gun sadly) on the BGA mounted components on the Logic board (took off the heatsinks first) as a lot of people reported this had solved similar problems. No Difference.
Next Steps:-
I was pretty confused at this point as the LG manual seems to indicate you should replace the Logic board if you have no power but the main connector voltages all test OK. On the other hand, threads & videos (especially ones related to the flashlight test) were suggesting it would be a failed backlight in this situation.
As I thought I'd probably destroy the TV for good if I took the screen apart to start following guides on how to test the LEDs, I said I may as well change the Logic board as LG suggest, and the engineer at the parts supply website I ordered from in the UK also thought that was the most likely fault.
I swapped the new logic board in today and the issue is still there. The only difference it has made is that the steady red standby LED now comes on as soon as the mains power is connected. It still blinks 3 times and then stays off when you try to take the TV off standby.
I've attached photos of the set as it currently stands with the new logic board. They seem to have got compressed a lot in uploading but I think you can still make out the details - if not, let me know and I will try to find a better way to upload.
I'll be very grateful for suggestions on what to try next. I was hoping the new logic board would be the answer but it didn't cost much so I'm not too cut up about the fact it didn't work. The TV will only go in the bin if I don't fix it so I'm happy to start disassembling the screen and de-soldering at this stage although if swapping a board would fix it I'd rather do that and play it safe.
Thanks in advance.
Having some trouble with an LG TV that failed a couple of months outside the warranty period.
Link to the model here:- http://www.lg.com/uk/tvs/lg-49UB850V
Before I start, I should say that although I've fixed a few simple things in the past, I know nothing about TVs other than what I've picked up trying to troubleshoot this and I'm not the sharpest when it comes to electronics or circuit diagrams so please bear with me if something simple goes way over my head
I have looked through as many threads, Youtube videos and repair guides as I can find but can't see any that seem to be the exact same issue. This thing is driving me up the wall so would really appreciate any input at all.
The Problem:-
Tried to turn the set on as normal one day and found it essentially dead. No Video. No Audio. No Backlight. No steady LED standby light on front of TV.
On pressing the standby button on the remote (or the joystick on the back of the TV), the standby LED blinks on-off 3-times and then stays off permanently until you disconnect & reconnect the power from the mains.
On the power board, there is a debug LED (LD701) which blinks amber on-off 5 times, repeatedly. This happens around 30 seconds after an attempt to turn the set on using the standby button.
What I've Tried:-
Firstly, I managed to find an LG service manual for a similar model that looks close enough for the instructions to be relevant. PDF attached.
Tried turning the set off from the mains for 12 hours and back on as sometimes suggested by LG support. No difference.
Checked the power board visually for any bad capacitors/resistors but can't see anything that looks bulged/burnt/damaged. I realise something could still have failed without any obvious signs but my soldering isn't great and I didn't think taking the big caps off the board to test them outside the circuit was a good idea before I'd checked the voltages.
Checked all the voltages on the 28-pin connector that joins the main board to the logic board as suggested by the service manual. Readings:-
3.5v = 3.54v (Standby & Power On)
12v = 11.79v (Power On)
24v = 23.7v (Power On)
SLCK, SW & YSYNC = All 1v (Power On)
Also spotted a row of test points for what I'm guessing are the LED circuits at the top of the PSU board so tested them as well in case anything jumped out.
P210 = 48.8v
EL85 = 0.8v
EL86 = 0.82v
EL87 = 0.8v
EL82 = 0.82v
EL83 = 0.8v
EL84 = 0.82v
EL79 = 0.76v
EL80 = 0.81v
EL81 = 0.85v
EL78 = 0.78v
EL77 = 0.78v
EL76 = 0.8v
Not quite sure what values these should be at so these readings didn't really tell me much.
I tried the flashlight test to see if I could pick up any image at all on the screen. Saw nothing - completely black.
Tried the hairdryer trick (Don't have a heat gun sadly) on the BGA mounted components on the Logic board (took off the heatsinks first) as a lot of people reported this had solved similar problems. No Difference.
Next Steps:-
I was pretty confused at this point as the LG manual seems to indicate you should replace the Logic board if you have no power but the main connector voltages all test OK. On the other hand, threads & videos (especially ones related to the flashlight test) were suggesting it would be a failed backlight in this situation.
As I thought I'd probably destroy the TV for good if I took the screen apart to start following guides on how to test the LEDs, I said I may as well change the Logic board as LG suggest, and the engineer at the parts supply website I ordered from in the UK also thought that was the most likely fault.
I swapped the new logic board in today and the issue is still there. The only difference it has made is that the steady red standby LED now comes on as soon as the mains power is connected. It still blinks 3 times and then stays off when you try to take the TV off standby.
I've attached photos of the set as it currently stands with the new logic board. They seem to have got compressed a lot in uploading but I think you can still make out the details - if not, let me know and I will try to find a better way to upload.
I'll be very grateful for suggestions on what to try next. I was hoping the new logic board would be the answer but it didn't cost much so I'm not too cut up about the fact it didn't work. The TV will only go in the bin if I don't fix it so I'm happy to start disassembling the screen and de-soldering at this stage although if swapping a board would fix it I'd rather do that and play it safe.
Thanks in advance.
Attached Files
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