LG 42lh4000 no picture

[hansp]

Hello,

tv model LG 42lh4000

mainboard EAX60686902 (0)
t-con EAX58017201 (9)
psu model EAX55357701/32 (rev 1.3)

The picture got dark from top right to bottom left while using and then it didn't show anything again. I can turn it on and the back light comes up, sound works, but no picture, OSD, ...

There's a soft hum (perhaps electric arc sound) around the two LIF42-inverters on the psu, but perhaps that's normal.

I tried to follow some material from LG Training Center for the 42LH50, but the 42LH4000 has some differences, e.g. there's no fuse or led on the t-con board.

Thanks for your help!

[Diah]

Re: LG 42lh4000 no picture

LH series suffer from over heating T-CON IC which effect on the board PCB sandwich.

the noise you hear from PSU not normal. its overload at MB. try disconnect the panel totally from T-CON and check the noise. either see if you disconnect just one side ribbon cable between T-CON and panel did the panel come as half white screen

[hansp]

Re: LG 42lh4000 no picture

Thanks for your reply!

I tried the following:
a) disconnected T-CON totally (from main and both side ribbon cables to panel)
b) disconnected T-CON from both side ribbon cables to panel
c) disconnected T-CON from left side ribbon cable to panel
d) disconnected T-CON from right side ribbon cable to panel

a)-d) There's no difference of back light (white screen) and arc sound.

The arc sound starts some moments after booting the TV: White screen starts quite intensive, after some milliseconds gets less intensive (normally there should be the logo) and right this moment arc sounds starts.

[Diah]

Re: LG 42lh4000 no picture

Thanks for your reply!

I tried the following:
a) disconnected T-CON totally (from main and both side ribbon cables to panel)
b) disconnected T-CON from both side ribbon cables to panel
c) disconnected T-CON from left side ribbon cable to panel
d) disconnected T-CON from right side ribbon cable to panel

a)-d) There's no difference of back light (white screen) and arc sound.

The arc sound starts some moments after booting the TV: White screen starts quite intensive, after some milliseconds gets less intensive (normally there should be the logo) and right this moment arc sounds starts.

if (d) its really half screen white then we do have issue at MB.
let start to measure the voltage from the socket at PSU to MB.. put yours DM black probe on the TV chassis and red probe on the pin of 20V then plug it on. notice yours DM measurement how it will read from start untill the buzzer noise come. same way do to the 12 volts pin.

[hansp]

Re: LG 42lh4000 no picture

Sorry, perhaps I was misunderstood - there is no half screen white -> a)-d) always full screen white.

I checked the voltage from the socket at PSU to MB:
- Written on the PSU board it says 20 V, but I measured the following after pressing the turn on button: 22.1 V, drops to 21.6 V, stays there for a moment, than buzzer noise starts and it stays at 21.5 V.
- 12 V: I measured 12.4 V the whole time.

[Diah]

Re: LG 42lh4000 no picture

Sorry, perhaps I was misunderstood - there is no half screen white -> a)-d) always full screen white.

I checked the voltage from the socket at PSU to MB:
- Written on the PSU board it says 20 V, but I measured the following after pressing the turn on button: 22.1 V, drops to 21.6 V, stays there for a moment, than buzzer noise starts and it stays at 21.5 V.
- 12 V: I measured 12.4 V the whole time.

upload photos please showing the screen how it look when you test options ( a and d ). to avoid any misunderstanding