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So I have this TV that when I press the power button, the backlight turns on but that is it. I figured it was the main board and replaced it and the same thing. I checked the output power on power board and see 13.2V what else can I try?
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Hi,
Just confirming that you checked all the relevant pins on the power board P201 connector to make sure that they all had 13.2V i.e. pins 4, 5, 6, 7 & 8?
With the TV in standby mode all these pins should be 7.8V
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Ok 2 questions regarding this, how to measure all the pins? I guess I need to remove board and power up with access to bottom of board? Also is when the TV is off with power button considered standby mode?
Yes Standby mode is when TV has power connected but the TV is not turned on. The colour of the power on led is showing standby (usually red) and not the colour it is when it's on.
I can't see it too well in the manual but usually you should be able to measure the odd numbered pins in the connector as they are exposed on the top side of the board. The pin numbering is marked on the board, either by an arrow denoting pin 1 or the number 1 at one end. Just don't short them out together with the meter's test probe bridging between them ;-)
Ok I was able to use a small probe and measure from the back of the connector and was able to test, and see that all the 13.2V and standby of 7.8V which is in spec. Only thing out of spec was the LED power output which was only 200V. Could this cause the symptoms I am seeing?
Not sure re the LED voltage.
Being low would mean that their brightness is diminished which could be just a result of a setting in the menus which is the mainboard.
Also if it were a power board problem causing them to be low then whatever is the cause doesn't seem to affect the voltage value being supplied to the mainboard.
I'm assuming that you may have only disconnected the cable between the mainboard and the power board at the mainboard end when you replaced it, so If you haven't already done so disconnect the power to the TV and then remove and check the cable at each end for corrosion and also perhaps check each wire for continuity from end to end. Alternatively check if the correct voltages are present at the mainboard end of the cable from the power board.
Update: Well I got a new main board, and that didn't fix it. So I also got a new T-Con board, and finally some improvement, but still not working. With the new T-Con and Mainboard, the screen is white, and can just barely see half of the LG logo on boot-up. One side of the screen is very white, and one side is mostly white whereas I can just see the logo. From looking at some youtube videos this may be a problem with lcd panels, and some people fix by putting tape over some of the clock lines to disable those portions of the LCD panel. Is this what I should try next? It is not obvoius on this TV which lines are the clock lines since there seems to be 2 ribbon cables per side. Any ideas?
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spam1 Here is a link to the service manual for your TV. Have a look on page 26 (of the PDF). That is the troubleshooting part, where symptoms are no audio and no video.
Basically, if the power board shows 13.2V then it suggests to check and replace the main board. Replace is the last step of course, as we’d like to repair if we can.
Could you take the main board out and take close up and high resolution (make sure of good focus) pictures, then update your question with those? Pictures of both sides of main board. Here is a guide on Adding images to existing questions.
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Ok pictures added.
@spam1 I don't see anything obvious at first glance, ie no burnt scorch marks or bad leads. I would suggest you set aside a little time to read through the troubleshooting section, ++, in the service manual I linked above. There are quite a few tests you can perform, mostly measuring voltages, with a DMM (digital multimeter). If everything checks out (doubt it will, but hard to pinpoint from pictures) then a new main board is a possible solution.
Ok so I was able to probe from the back of the connectors, so could measure all the voltages listed on "A9" of the service manual. And they all check out except for the "LED voltage Check : P801" which is supposed to be between 216-274, but I only see 200V. I tried testing without the LED's connected, to see if they were pulling the voltages down, but I then see 0 volts, so not sure.
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