LG 42LG50 no backlight or display

[Daveleone]

Re: LG 42LG50 no backlight or display

If you can disconnect that cable to the T-CON board then the backlights come on and stay on then your inverters/lamps are OK. As I indicated, you should now see the pictures on the screen. You TV has what is called dynamic contrast, the T-CON controls the backlight level based on video scenes.

Ok, there is still no picture, just backlight. What can I do as a next step to determine if the problem is the main board, the t-con, or the panel?

[budm]

Re: LG 42LG50 no backlight or display

Find out if you do have 12VDC on both end so of the SMD fuse on the T-CON board with ref. to chassis GND.

[Daveleone]

Re: LG 42LG50 no backlight or display

Find out if you do have 12VDC on both end so of the SMD fuse on the T-CON board with ref. to chassis GND.

Yes. Measured 12.44v on both sides of FP1 (which I'm assuming is the fuse we're talking about).

[budm]

Re: LG 42LG50 no backlight or display

OK, try having one ribbon cable between the LCD panel and the T-con board connected one at a time to see what you will get on the screen.
Right now without that cable between the T-CON and the Master inverter board connected, do you still have full control of the TV, I.E. able to turn TV on and off?

[Daveleone]

Re: LG 42LG50 no backlight or display

OK, try having one ribbon cable between the LCD panel and the T-con board connected one at a time to see what you will get on the screen.
Right now without that cable between the T-CON and the Master inverter board connected, do you still have full control of the TV, I.E. able to turn TV on and off?

Disconnected each T-Con->Panel ribbon cable one at a time. Made no difference.

Yes, I can now turn the power on and off via the power button on the front bezel.

[lookimback]

Re: LG 42LG50 no backlight or display

OK, try having one ribbon cable between the LCD panel and the T-con board connected one at a time to see what you will get on the screen.
Right now without that cable between the T-CON and the Master inverter board connected, do you still have full control of the TV, I.E. able to turn TV on and off?

Be sure to cycle power off whenever disconnecting or reconnecting the ribbon cables. I fried a 60" Sharp panel like that once. Additionally, if you removed each ribbon cable, but didn't cycle the power when doing so, then repeat that process, cycling power as I just described, and you may get different results.

[Daveleone]

Re: LG 42LG50 no backlight or display

Be sure to cycle power off whenever disconnecting or reconnecting the ribbon cables. I fried a 60" Sharp panel like that once. Additionally, if you removed each ribbon cable, but didn't cycle the power when doing so, then repeat that process, cycling power as I just described, and you may get different results.

I did. I unplugged the TV, removed one cable, plugged the TV back in. Then repeated for the other cable.

[budm]

Re: LG 42LG50 no backlight or display

Well, we need to check the Voltages on the test points on the T-CON board next.
You can see bare copper pads with label for each one, so far I can see:
VD33V
V25V
VDD,
VGH
VGL
VAA

so look for pad with V????.............

[Daveleone]

Re: LG 42LG50 no backlight or display

Well, we need to check the Voltages on the test points on the T-CON board next.... look for pad with V????.............

Here are all the pads I found and tested (I bolded the Vxx ones). These values are the same whether the ribbon cable from the master inverter is plugged in or not, except where noted in italics:

GND 0
SDA 3.3
VIN 12.44
SCL 3.3
TSTPGW 0

DRL1 0
OE1 3.3
STV 0
CKV 0
VSCN 0

VDD 3.3
VDA 0
VCOM 0
VGH 11.06
VGL -5.57

VST -0.18
SIN1 0
SIN2 0
GRL2 3.3
B_STH 3.3
B_TP1 0 (NOTE: when the ribbon cable from the master inverter is plugged in, this is 2.22v)

B_STHR 0 (rising slowly)

DIM_O 0
DIM_I 0.1 (rising slowly) (NOTE: when the ribbon cable from the master inverter is plugged in, this is 3.33v, even when the ribbon cable is disconnected if I test the pin on the inverter side it is 3.4v)

VD33V 3.3
VGHP 11.1
VAA 0
V12V 12.44
V25V_A 2.49
VREF 0

[Daveleone]

Re: LG 42LG50 no backlight or display

.

What next?

[budm]

Re: LG 42LG50 no backlight or display

https://www.badcaps.net/forum/showpo...6&postcount=18

Some of the Voltages are low and some are missing, I.E. Vref. should not be 0V.
A this point you can try new T-CON board.

From Andrew in the link above:
1. Vin: 12V (we confirmed as present)
2. Vdd (Vlogic, Vddd): 3.3V
3. Vda (Vs, Vsource, Vdda Avdd): 14V to 20V
4. Vgh (Vgon, Von, Vddg): 20V to 30V
5. Vgl (Vgoff, Voff, Veeg): -5V to -7V

[Andrew F. Ali]

Re: LG 42LG50 no backlight or display

,

[Daveleone]

Re: LG 42LG50 no backlight or display

A this point you can try new T-CON board.

Ordered. I'll post results as soon as it arrives (scheduled to arrive 7/24).

[Daveleone]

Re: LG 42LG50 no backlight or display

A this point you can try new T-CON board.

Received the new T-Con today.

No joy. Same exact results (same behavior, same voltages) with the new T-Con. So...main board? Is VDA on the T-Con supplied by the main board (over the LVDS cable)? If so, a bad main board would explain lack of VDA on the T-Con and the error signal sent to the inverters. And maybe the error signal sent to the inverter would also explain why DIM_I on T-Con, which is coming from DIM_O on the master inverter, is also high. Example: Main board is bad. It doesn't send the proper voltages to T-Con. It does send ERROR to master inverter. Inverter sends DIM_O high to T-con to indicate the error. Maybe? I don't know...thoughts?

[Daveleone]

Re: LG 42LG50 no backlight or display

Or do you think I got a 2nd bad T-Con?

[budm]

Re: LG 42LG50 no backlight or display

So do you get the same readings as in post 30?
What is the LCD panel model number?

[Daveleone]

Re: LG 42LG50 no backlight or display

So do you get the same readings as in post 30?
What is the LCD panel model number?

Yes, same readings as post 30 with one minor exception - B_TP1 is 2.22v on the original T-con and it is 3.3v on the new T-Con, when the ribbon cable is unplugged. When the ribbon cable is plugged in B_TP1 is 0v on both T-Cons.
The panel has the following labels on it: "M$44-D024408 - L$T13A423068433524" and "V420H1-L12 Rev. C1 - C4C140185120364 - E207943"

[syaoran123]

Re: LG 42LG50 no backlight or display

Can you inspect the blue polymer caps on the psu next to the transformers on the bottom left hand side? Look for any signs of damage.

[Daveleone]

Re: LG 42LG50 no backlight or display

Can you inspect the blue polymer caps on the psu next to the transformers on the bottom left hand side? Look for any signs of damage.

I gave them a look over. No visible damage.

[Andrew F. Ali]

Re: LG 42LG50 no backlight or display

I am beginning to wonder if your Panel is bad now that I've read all the posts again.