Hi, I'm looking for some help with attempting to troubleshoot and hopefully repair my trusty LG55" TV.
I'm reasonably comfortable working with electronics, but far from expert level! I have more experience with auto-electrics than anything.
We recently had a power cut while the TV was on, and since then, when the TV is switched on at the wall, the red standby light comes on like normal. Then. when you press the power button on the remote or the TV to switch it on from standby, the standby light flashes 3 times and then goes out. There is no audio or video at all and no LG logo on the screen. The screen stays completely black. I've used a flashlight to check and there is no life on the screen at all.
The model is LG 55UB850V. I have taken the back off the set and observed the following internally.
The power supply board is model PCB: EAX65613901 (1.6), LG P/N: EAY63149401 REV 1.0 2014.01.27
The Main Logic board is model L#41V EAX65684604 (1.0)
The T-CON board is mode V14 TM120 UHD Ver 0.6, LG P/N: 6870C – 0502C
When the set is in standby mode, there are no LED's lit up on either the power supply board or the main board. When I press the power button on the remote or the TV, the red standby led flashes 3 times and then goes out. The red led LD2300 on the main logic board is lit up solid and the red led LD1900 on the main logic board lights up briefly for around 1 second then goes out.
After 60 seconds in this state, the amber LED LD701 on the power supply board starts flashing a sequence of 5 flashes, and then 5 seconds off, then 5 flashes, then 5 seconds off etc. This carries on seemingly indefinitely.
During this time there is absolutely nothing on the screen.
If I leave the set in this state, as if the screen should be on, and with the amber LED LD701 repeatedly flashing it's 5 flash sequence, for around 20 minutes or so, then use the remote to put the set back into standby, then again use the remote to turn the set on form standby, it springs back into life.
It seems the set needs to have constant power, in the normal 'on' state for around 20 minutes or so before it will then start to work, once put into and back out of standby.
Can anyone suggest what might cause this behaviour? If I unplug the set form the mains, and then plug it back in again, it fails to work, until I have left it in the 'on state for 20 minutes or so.
Could this be cause by failing capacitors that are unable to keep their stored voltage once the mains power is cut? Could it take 20 minutes or so for them to get to full capacity in order to allow the set to start functioning correctly?
The 28 pin connector on the power board has all the correct ground, 3.5v, 12v, and 24v readings when tested, even when the screen isn't on or working.
Thanks for any help!
EDIT: My 20 minute theory has gone out the window - it must have just been a fluke that it started working. During this 'working' spell, the tv was still face down on my bed with the back removed while I was testing. After reassembling the back and putting the TV back on its stand, I couldn't get it to switch on again, even after leaving it in standby as well as in what should be the 'on' state overnight.
After taking the back off again, I can see that what DOES happen after 20 minutes of being in the 'on' state, all LED's turn off, and the red standby light goes solid again - must be some sort of timeout or power saving setting, making it go back into standby mode.
I'm reasonably comfortable working with electronics, but far from expert level! I have more experience with auto-electrics than anything.
We recently had a power cut while the TV was on, and since then, when the TV is switched on at the wall, the red standby light comes on like normal. Then. when you press the power button on the remote or the TV to switch it on from standby, the standby light flashes 3 times and then goes out. There is no audio or video at all and no LG logo on the screen. The screen stays completely black. I've used a flashlight to check and there is no life on the screen at all.
The model is LG 55UB850V. I have taken the back off the set and observed the following internally.
The power supply board is model PCB: EAX65613901 (1.6), LG P/N: EAY63149401 REV 1.0 2014.01.27
The Main Logic board is model L#41V EAX65684604 (1.0)
The T-CON board is mode V14 TM120 UHD Ver 0.6, LG P/N: 6870C – 0502C
When the set is in standby mode, there are no LED's lit up on either the power supply board or the main board. When I press the power button on the remote or the TV, the red standby led flashes 3 times and then goes out. The red led LD2300 on the main logic board is lit up solid and the red led LD1900 on the main logic board lights up briefly for around 1 second then goes out.
After 60 seconds in this state, the amber LED LD701 on the power supply board starts flashing a sequence of 5 flashes, and then 5 seconds off, then 5 flashes, then 5 seconds off etc. This carries on seemingly indefinitely.
During this time there is absolutely nothing on the screen.
If I leave the set in this state, as if the screen should be on, and with the amber LED LD701 repeatedly flashing it's 5 flash sequence, for around 20 minutes or so, then use the remote to put the set back into standby, then again use the remote to turn the set on form standby, it springs back into life.
It seems the set needs to have constant power, in the normal 'on' state for around 20 minutes or so before it will then start to work, once put into and back out of standby.
Can anyone suggest what might cause this behaviour? If I unplug the set form the mains, and then plug it back in again, it fails to work, until I have left it in the 'on state for 20 minutes or so.
Could this be cause by failing capacitors that are unable to keep their stored voltage once the mains power is cut? Could it take 20 minutes or so for them to get to full capacity in order to allow the set to start functioning correctly?
The 28 pin connector on the power board has all the correct ground, 3.5v, 12v, and 24v readings when tested, even when the screen isn't on or working.
Thanks for any help!
EDIT: My 20 minute theory has gone out the window - it must have just been a fluke that it started working. During this 'working' spell, the tv was still face down on my bed with the back removed while I was testing. After reassembling the back and putting the TV back on its stand, I couldn't get it to switch on again, even after leaving it in standby as well as in what should be the 'on' state overnight.
After taking the back off again, I can see that what DOES happen after 20 minutes of being in the 'on' state, all LED's turn off, and the red standby light goes solid again - must be some sort of timeout or power saving setting, making it go back into standby mode.
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