LG 32LV5500 CH:LT12E goes on but no image, BL or sound

[yoritomo]

Hello all

This TV set is a LG 32LV5500 the chassis number is LT12E available service manual at Electrotanya.
Main board number : EAX64104702(1)

When pushing stby button on the remote the TV goes ON as the red led it turning white, no sound or images , back light is still OFF but working as I could force it to start, I only got a blank black screen.

then i checked the power outputs, 12, 24 and 3.5V are all ok, no have any 5V from power supply board.

If I check pin 10 of IC602 which seems to be BL-on i see 3.5V there but no reaction from backlight.

There are the tensions i could find on the coils :

L1807, L1808 : 0.78V
L1810, L1811 : 0.67V
L505 : 0.94 V
L508 : 3.34 V
L509 : 5.05 V
L516 : 5.15 V

Where is the 1.5V for the rams ?

There is an image from the board i could find on the net, except the connectors i don't have on this set strangely.


Thank you again for your great help.

[DeeJayAlex]

Re: LG 32LV5500 CH:LT12E goes on but no image, BL or sound

Hello
You have 5v and 3,3 v on LVDS CONNECTION?

[yoritomo]

Re: LG 32LV5500 CH:LT12E goes on but no image, BL or sound

Hello

On the larger LVDS connector I could measure 3.24v on pin 4 and 5
Nothing on the 4 last pins mentioned Panel_VCC.

[yoritomo]

Re: LG 32LV5500 CH:LT12E goes on but no image, BL or sound

I guess back light control and panel power supply are controlled both together when the set is ready.
I perhaps may try the internal t-con board auto test color bars to check the validity of the t-con board and panel, but i am sure the result would be correct because i think the culprit is the main board .


What would you do first ?

Thank you for your ideas.

[budm]

Re: LG 32LV5500 CH:LT12E goes on but no image, BL or sound

Can we see the whole back side of the TV showing all the boards?
Since you do have BL-ON (at INV_ON pin) signal, what DCV do you have feeding the LED driver power supply and at the LED connectors?
So for sure you can force on the backlights, but that does not make sense if you indcated that you do have BL-ON signal.
How about the dim control signals A-DIM, P-DIM? What do you get?
Panel_VCC is the DCV for running the T-CON, it is fed through switched MOSFET.

[Diah]

Re: LG 32LV5500 CH:LT12E goes on but no image, BL or sound

there are always simple test needed to do in order narrow the fault. you wrote no sound and picture, no backlight and 12 & 24 volts okay. did you test with torch light at dark room if you have picture ? did you try to turn on or off with RC if it work or not ?

[yoritomo]

Re: LG 32LV5500 CH:LT12E goes on but no image, BL or sound

This tv set is exactly this as this picture i could find on the net except for the video connectors on main board.


I could find the signal INV_CTL on the chip but it is not going to the power supply connector, that is why i was wondering and decided to force it to see if any image present, no luck. Perhaps INV_CTL and BL_ON are not relative ?

The +24V is present and correct but i need to check again the led dc power value A-DIM and P-DIM, that tv is on my labo, i am currently at home.

Thank you very much, i will give this value when i am going there.

[yoritomo]

Re: LG 32LV5500 CH:LT12E goes on but no image, BL or sound

Diah , yes i wrote it in the first post, when i turn on manually the backlight, just a black blank screen, no osd ..
Yes with remote control it works, the led is turning white and all power outputs are on as i described already, it means at least the micro controller is responding.

[budm]

Re: LG 32LV5500 CH:LT12E goes on but no image, BL or sound

https://www.badcaps.net/forum/showth...549#post687549
The INV_ON and the DIM command pins are on that white connector of the main board to goes to the Power supply board, you see the labels for each pin on that connector.
The problem right now is that you need to that PANEL_VCC to run the T-CON baord also find out if you do have DCV on that INV_ON pin on the main board connector or not.

[yoritomo]

Re: LG 32LV5500 CH:LT12E goes on but no image, BL or sound

As answer to the question of Budm, i did the following measures this afternoon :

On the output connector of the driver board, i could find 52V on the first and last pin when the Back light is forced ON. and P-dim = 3.15V A-Dim= 0v.

The INV_ON is 0V (of course unless i force it)

I made a test, forced backlight on and applied 12V coming from the the other connector to Panel_vcc nothing works because it is falling to 1.5V either that 12V power is too weak or perhaps abnormal consummation on the T-con board or panel itself. Today i had no time to apply an external 12v power supply to know what is wrong there. I will do next.

Thank you for your help again

[budm]

Re: LG 32LV5500 CH:LT12E goes on but no image, BL or sound

When you applied 12V to the TCon board, did you completely Remove ALL the wires for 12V going back to the main board first, if not you had just cause more damages to the main board.
Same for any force on.

[yoritomo]

Re: LG 32LV5500 CH:LT12E goes on but no image, BL or sound

I have disconnected L1501 to prevent it

[budm]

Re: LG 32LV5500 CH:LT12E goes on but no image, BL or sound

Typical T-CON requires 3~5A to run, you can look up the spec sheet of the LCD panel to get the actual spec.

[budm]

Re: LG 32LV5500 CH:LT12E goes on but no image, BL or sound

I have disconnected L1501 to prevent it

Where is the L1501 on the main board?

[yoritomo]

Re: LG 32LV5500 CH:LT12E goes on but no image, BL or sound

yes it is the one providing 12v to the panel

[budm]

Re: LG 32LV5500 CH:LT12E goes on but no image, BL or sound

At this point you do have main board problem.

[yoritomo]

Re: LG 32LV5500 CH:LT12E goes on but no image, BL or sound

IC602 is the micom chip, the pin 10 is sending order to start the back light, looks like the 0 V of A-DIM is connected directly to the line of INV_ON , and the order of PANEL_VCC is coming from the t-con itself, without it, no 12V PANEL_VCC will be provided. How t-con determines if needs to feed the panel or not ?

May it be a faulty T-Con board ?

Or how should i start to troubleshoot the motherboard anyway? If no reply from the ram would it occurs such fault ?

EDIT: i have an oscilloscope to try deeper tests and i would like to learn more about a such problem.

[budm]

Re: LG 32LV5500 CH:LT12E goes on but no image, BL or sound

The panel_VCC feeding the SMD fuse to the T-CON BOARD through the LVDS cable by the way of power MOSFET Q507 on the main board that is turned on the by MICOM.
A-DIM (Analog Dimming control signal 0~5V, 5V = Max lamp brightness) is variable signal, so it cannot be the same as the INV_ON (HIGH or LOW signal), there is also PWM_DIM (Pulse Width Modulation Dimming control), which depends on which one the manufacturer will use, ANALOG or PWM.
When power switch is activated, the main board will send PS-ON to turn on the rest of the power supply, after that the INV_ON signal is sent to turn on the backlights circuit, then the MOSFET Q507 for the 12V feeding the T-CON is turned on to supply the Voltage to run the T-CON.
Look at PDF page 52

[yoritomo]

Re: LG 32LV5500 CH:LT12E goes on but no image, BL or sound

Some part of schematics are better to discuss, i could not find any output from micom to control Panel VCC.

There is the 12 power PANEL_VCC switching circuit :


An here is the control pin coming from the T-Con board by the lvds 54 pins connector :

[budm]

Re: LG 32LV5500 CH:LT12E goes on but no image, BL or sound

Well, look at PDF page 31, the MICON IC602 OUTPUT PIN 11 MODEL_OPT_1 is the PANEL_CTL SIGNAL PIN which is used for turning on the power MOSFET to supply PANEL_VCC, that same control signal is also to that pin 10 SHARP_OPT, that is RECEIVING PIN NOT output pin.
When PANEL_CTL goes LOW the MOSFET is turned on to supply 12V to T-CON.
You need to look at the schematic really well, and how can the T-CON turn on its own power to supply the 12V to the SMD fuse when it needs the 12V to be present first for it to do anything, common logic..
Look up the spec sheet of the LCD panel to find out what that SHARP_OPTION pin is for.