Toshiba 40L3433DG backlight OK but no picture

[budm]

Re: Toshiba 40L3433DG backlight OK but no picture

I don't have VDD, VGH, VGL or maybe they use different naming. What do VDD, VGH, VGL stand for? Maybe I can find some equivalency with different naming.

I have VON, L_L, L_H but they are close to the LCD bias IC so most likely not involved with RT6917GQW.

I read 74 Ohms between GND and AVDD (independently of multimeter's connection direction) and 11,24 KOhms between GND and HVIN_12V for one direction and 14 KOhms for the other direction.

There should be caps connected to that AVDD test point, check to to see if they also show 74 Ohms reading.
Typical T-CON Voltages
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

Some learning:

[Pierre95]

Re: Toshiba 40L3433DG backlight OK but no picture

There are 4 caps between AVDD and GND. Is that one or several caps are partial shorts creating the 74 ohms resistance or is this value typically of the AVDD output?

Interesting reading...

[budm]

Re: Toshiba 40L3433DG backlight OK but no picture

Multiple caps connected to AVDD, VGL, VGH are typical.
74 Ohms reading on AVDD is not normal.
More learning about typical LCD Bias power supply IC.

[budm]

Re: Toshiba 40L3433DG backlight OK but no picture

HVIN_12V: 0,17V
AVDD: 0V
VCC_1.8V=0V
VCC_1.15V=0V
VCC_3.3V=0V

Are 100% sure that you have 12VDC at both ends of the fuse on that integrated T-CON board?
Try tracing the HVIN_12V to see if it goes to the V12IN (fuse) via some kind of inductor (L).
See PDF for more info about T-CON.

[Pierre95]

Re: Toshiba 40L3433DG backlight OK but no picture

That could be caused by the caps themselves or internal RT6917GQW failure.

[budm]

Re: Toshiba 40L3433DG backlight OK but no picture

Yes, it can be the caps, the RT, or the loads connected to that AVDD power supply output.
Look at my post #24, I just add the RT6905 T-CON schematic, you can see how VIN_12V is connected to HVIN12V, that should give you enough clue.

[Pierre95]

Re: Toshiba 40L3433DG backlight OK but no picture

You may have posted #24 while I was editing post #25. I will have detailed reading of the attached documents you provide, and recheck VIN_12V's fuse and see how it connects to HVIN_12V.

[Pierre95]

Re: Toshiba 40L3433DG backlight OK but no picture

Please find attached connexion routing for HVIN_12V.

As I understand from your schematics, HVIN_12V is issued via pin 46 (LX1) and fed through L104 to generate actual HVIN_12V.

As per my understanding, there is not only a coil between VIN_12V and HVIN_12V as HVIN_12V is generated by RT6905 from VIN_12V.

There may be something that prevents HVIN_12V from being activated.

Or is LX1 an input? Not easy to understand how it works without 6905 or 6917 datasheet.

[budm]

Re: Toshiba 40L3433DG backlight OK but no picture

Please find attached connexion routing for HVIN_12V.

As I understand from your schematics, HVIN_12V is issued via pin 46 (LX1) and fed through L104 to generate actual HVIN_12V.

As per my understanding, there is not only a coil between VIN_12V and HVIN_12V as HVIN_12V is generated by RT6905 from VIN_12V.

There may be something that prevents HVIN_12V from being activated.

Or is LX1 an input? Not easy to understand how it works without 6905 or 6917 datasheet.

No, HVIN_12V comes from switched P-CH MOSFET Q109, that switched 12V is then boosted up to 16.6V (AVDD_16.6V) by boost converter circuit. See picture attached.

[Pierre95]

Re: Toshiba 40L3433DG backlight OK but no picture

Thanks for clarification! And I guess VIN_12V gets switched by RT6905 through GD? Is the switching operation initiated through an I2C command sent over the SDA SCL lines or does it start automatically?

I don't see any transistor which may act as Q109 in the proximity of RT6917 on my TCON. Maybe it is actually implemented within RT6917. There is a transistor labelled Q1 but it is located near ICK1 (see attached picture).

[budm]

Re: Toshiba 40L3433DG backlight OK but no picture

I need good clear picture like that on around the RT.
May be you can take good clear pictures in sections and then I can stitch them together.

[Pierre95]

Re: Toshiba 40L3433DG backlight OK but no picture

Please find attached the sequence of pictures for the whole TCON.

[budm]

Re: Toshiba 40L3433DG backlight OK but no picture

Thanks for the good pictures.
I do not remember if you report the resistance reading between VIN_12V and the HVIN_12V or not.
So far I do ne see any switched MOSFET for the HVIN_12V

[Pierre95]

Re: Toshiba 40L3433DG backlight OK but no picture

Resistance between HVIN_12V and VIN_12V is arround 74K in one direction of measurement and 60K in the other direction but the value increases slowly as if some capacitor were involved.

[khaled1981]

Re: Toshiba 40L3433DG backlight OK but no picture

Hi sir i have the same problem with the same panel i have not 12v in lk1 do you have schematic please