LG 42LW6500 no backlights

[maxvalutech]

Side of the road find and in good condition. Power cord cut off but luckily I had one on hand with special fitting for these sets. Opened it up fitted cord and got nothing on main caps but found main fuse open so piggy backed another to it. This resulted in the 3.5v standby coming up and switching on I measured all good voltages on main caps plus 12v and 24v measured OK. Main connector is 24pin and couldn't get the pin outs under the board at this stage. No real indication, nothing to go by in screen or sound but I have a feeling the set is starting just not displaying. The two caps at top of power board look like they may be associated with led circuit as they show 37v but no voltage at all on led connectors (2) to the LEDs. Guidance needed and appreciated.

[Andrew F. Ali]

Re: LG 42LW6500 no backlights

How you lucky, so???.....So the PSU is OK. The Main Bd. seems to be OK too as PSON working and set staying ON. The LEDs could be bad. Try the flashlight test and see if you have picture. Look at the T-CON Bd. Measure VGL, VGH, Vin, Vdd and Vda voltages. If these awithin spec then I'll replace those LED backlights. I'm not too sure but this could be an edge-lit backlight system.

[maxvalutech]

Re: LG 42LW6500 no backlights

Will do. I've not seen so many lead wires going into the LEDs before and wondering how they are all connected - not easy to see in pic but each connector the last wire is black for earth return I imagine but are the white ones individual strings!!. And if so why no voltages at all on those two connectors?? And yes edge lit.

[R_J]

Re: LG 42LW6500 no backlights

Usually the LED+ will have the led voltage to the strings, the vc_** are the returns,and are controlled by an ic/transistors. You may need to have your probe on the pin, then turn the power on because if there is a fault with any led string the led power is turned off

[Andrew F. Ali]

Re: LG 42LW6500 no backlights

You may have to tear down the Panel to change out the LED strip/s.

[maxvalutech]

Re: LG 42LW6500 no backlights

Well a complete turnaround. When I took all the armour off the tcon board no voltage going to it. So my suspicion wrong (again) and main not generating that voltage or screen turn on apparently. Tried prodding, freezing, heat gunning without success so in the oven it went and yes it all came on nicely when refitted. BUT when main was pulled out I found under that board a 100uf 16v electrolytic had been soldered in between pin3 of tuner and earth - not an original by the look of it and for what purpose I don't know. When set came on I could see it was tuned for channels adjacent to ours, I tried to retune with no go so I changed that cap in case I'd baked it bad but still no go. Tuners work off 5v I think so will now have to check its circuits if I can - know almost zilch about them.

[budm]

Re: LG 42LW6500 no backlights

https://www.badcaps.net/forum/attach...7&d=1526449969
Can I get better picture?
I am trying to find out what your PCB numbers are, I see EAX62865????
I am also trying to read the Voltage chart on the board, it looks like the LED+ Voltage is 5? V DC

[maxvalutech]

Re: LG 42LW6500 no backlights

Yes budm eax62865401/8 for PSU and eax63686303(3) for main. I can't see any volts near LED+ but I have 54v on each connector when running now. I also add to above post that both HDMI and AV work OK.

[maxvalutech]

Re: LG 42LW6500 no backlights

I have 2 phones same model but one takes better pics than the other for some reason. All input done from these phones.

[budm]

Re: LG 42LW6500 no backlights

https://www.badcaps.net/forum/attach...6&d=1526535451
It looks like the LED+ Voltage with load should be around 5x? (I still cannot clearly read the chart), so the 30 something Volt may be the input Voltage feeding the boost converter circuit.
So the backlights are on right now?

[maxvalutech]

Re: LG 42LW6500 no backlights

Yes all working well other than the tuner. Been going for several hours turned it on and off a few times, all menus and inputs work. Got to get to voltages around tuner - do have circuit info so will remove main board again and do a visual and few tests first.

[budm]

Re: LG 42LW6500 no backlights

If the backlights stop working again and you are getting only 30V or so, then check to see if the BL-ON is still present or not when it fails.
BTW, solder joints are good?

[maxvalutech]

Re: LG 42LW6500 no backlights

This set has held up well so far. All menus work as do HDMI and AV inputs showing a good full picture. BUT I still cannot get to tune stations - it goes through the procedure OK but gets none. So the tuner isn't working and I have checked circuit items but all test OK. Why the small cap was added I don't know but possibly gave trouble before and this was the fix but not now. Will have to run board connected but out of set to test voltages BUT again is this safe to do for the board e.g. floating earths etc ????

[maxvalutech]

Re: LG 42LW6500 no backlights

Decided to solder wires to the 5v, 3.3v & 1.2v pins on tuner and test that way. First two are good but only 0.26v on the last. Now ive got to follow that circuit back and smds so small and close very difficult to check let alone identify from part numbers all over the place!

[maxvalutech]

Re: LG 42LW6500 no backlights

The 1.2v circuit goes back from tuner via a 10uf 16v cap then 2 x 11k resistors all smd to pin 6 out on ic2208 which is a voltage regulator AP2132MP-2.5TRG1. I measure around 0.25v on that pin whereas input checked at 3.3v. Specs say min output should be higher. Tried both freeze and heat on the ic but no change. Have ordered a few and will see how it goes with a replacement ic.

[MrMagoo]

Re: LG 42LW6500 no backlights

Subscribing to this thread.
I picked up two of these of the side of the road within 500metres of each other. backlight not coming on. But it powers on standby light changes from red to purple.

[Andrew F. Ali]

Re: LG 42LW6500 no backlights

Without you posting any voltage readings and guessing since the standby light changes from red to purple and remaining purple the backlights could be the culprit. Start your own post for this TV with photos and voltage readings and more help will come to you.