Another LG, 55ln5100 power issues

[Redrebel10]

Re: Another LG, 55ln5100 power issues

Update, got new (used main board installed) still had 3.5v standby voltages, powered on and no backlights came on. Only voltage readings on psb were both 3.2 standby and pwr-on and dvr-on both read 3.2. I unplugged the TV while on and plugged it in and backlights flashed on for a second. I then unplugged the tv and disconnected tcon board from main board. After plugging TV back in the backlights came on and stayed d on. All 12v readings were there along with both 24v readings. Pwr on and dvr still read 3.2 and pdim1 reads 1.1
and pdim2 reads 1v. Back to where I originally began and assuming bad tcon board

[Redrebel10]

Re: Another LG, 55ln5100 power issues

OK so I did another tcon test, I left it plugged into main board and removed both ribbon connectors going to panel. Unplugged TV and plugged back in and the backlights stayed on. I touched my meter to the fuse on tcon to see if it had 12v and the back lights went out immediately. Could have been a coincidence I suppose

[nomoresonys]

Re: Another LG, 55ln5100 power issues

If there's ever a questionable reading it pays to take it out of circuit and test again, it's not really that hard.

[diif]

Re: Another LG, 55ln5100 power issues

OK so I did another tcon test, I left it plugged into main board and removed both ribbon connectors going to panel. Unplugged TV and plugged back in and the backlights stayed on. I touched my meter to the fuse on tcon to see if it had 12v and the back lights went out immediately. Could have been a coincidence I suppose

It depends how your meter was set, you might have shorted 12v to ground.

[Redrebel10]

Re: Another LG, 55ln5100 power issues

If there's ever a questionable reading it pays to take it out of circuit and test again, it's not really that hard.

At this point just curious to know why backlights come on with tcon unplugged

[Redrebel10]

Re: Another LG, 55ln5100 power issues

It depends how your meter was set, you might have shorted 12v to ground.

It was set to 200 DC, guess that's irrelevant since backlights only work with tcon unplugged

[Redrebel10]

Re: Another LG, 55ln5100 power issues

Help.

[budm]

Re: Another LG, 55ln5100 power issues

So if you do not have the cables between LCD panel and the TC-ON board connected, but the cable between the main board and the T-CON is connected, do you get 12vdc at both ends of the T-CON fuse with ref to chassis GND?
BTW, always plug or unplug anything only when TV is NOT plugged into the outlet since the standby power supply is ALWAYS running.

[Redrebel10]

Re: Another LG, 55ln5100 power issues

With both ribbon cables detached from lcd. TV plugged in and hit power button. Backlights do not come on so no voltage at tcon fuse. Same set up, both ribbon disconnected but tcon connected to main board. I unplug TV from the wall and plug back in. Backlights come on and stay on and now have 12v on both sides of tcon fuse

[budm]

Re: Another LG, 55ln5100 power issues

With both ribbon cables detached from lcd. TV plugged in and hit power button. Backlights do not come on so no voltage at tcon fuse. Same set up, both ribbon disconnected but tcon connected to main board. I unplug TV from the wall and plug back in. Backlights come on and stay on and now have 12v on both sides of tcon fuse

So it is the same setup as in your post 42 (and the same as I instructed in my post 48:"So if you do not have the cables between LCD panel and the TC-ON board connected, but the cable between the main board and the T-CON is connected, do you get 12vdc at both ends of the T-CON fuse with ref to chassis GND?") but this time the backlights did not go out when you put your meter to check for the 12V on the T-CON, right?
BTW, of cause there will be no 12V on the T-CON if the cable between Main board and the T-CON is not connected.
Also during the test, you do have the T-CON board mounting screws in place, correct>
Since you now have backlights and the 12V at T-CON without having having the cable between T-CON and the LCD panel connected, what happen if you connect the cable between T-CON and the LCD panel at a time? Also check to see if the 12V goes away or not.

[Redrebel10]

Re: Another LG, 55ln5100 power issues

Correct tcon is connected to main board. Using the power button the backlights will not come on. Unplugging the TV while power is on and plugging back in the backlights come on and all readings are normal while backlights are on I connected the 2 ribbon cables from lcd to tcon board (yes screwed down) voltage on both ends of tcon fuse are 11.3

[will62]

Re: Another LG, 55ln5100 power issues

I don't believe that 11.3V is high enough to clear the Power Detect on the main board (see attached). Whatever is pulling down the 12V, may be pulling it down slow enough (relative to processor speed), That the power detect instruction is cleared before the voltage reaches the minimum threshold. Once it goes below that threshold, a flag bit is set on the IC. When you turn it off and on with the power button, you are not resetting any flag bits, because standby voltage is still there. When you unplug and replug, you are clearing all flag bits, and the process starts over.

Either the PSB is not putting out its rated 12V, or something on t-con or panel is pulling it down. That part would be putting out some heat if you want to try freeze spray.

[budm]

Re: Another LG, 55ln5100 power issues

Correct tcon is connected to main board. Using the power button the backlights will not come on. Unplugging the TV while power is on and plugging back in the backlights come on and all readings are normal while backlights are on I connected the 2 ribbon cables from lcd to tcon board (yes screwed down) voltage on both ends of tcon fuse are 11.3

So you connected BOTH ribbon cables between the T-CON and the LCD panel while the TV is still ON (which is the bad thing to do and I already told you to always unplug the TV from the outlet before removing or installing the cables unless you want to cause damages), the backlights stay on and the 12V is present at the TC-ON fuse, so what do you see on the screen at this point since the backlights stay on when you have all the cables back in place?
What happen if you connect the cable between T-CON and the LCD panel ONE at a time?

[Redrebel10]

Re: Another LG, 55ln5100 power issues

Thanks for the info will62

Budm. I read your previous post as you wanted me to plug the lcd to tcon while I had the backlights on. However no picture appears, just a lit up screen. I'm just about ready to wave the white flag on this one

[budm]

Re: Another LG, 55ln5100 power issues

Post 48: I did say NOT to plug/unplug the cables while TV is PLUGGED in. I gave up too.