Toshiba 48L5463DN no picture, backlight on

[Stigsolbjerg]

As title says, its a vestel inside. power led flikering red and green 12 times. Backlights comes on at nr 9 red. Nothing burnt or swollen caps. Tried switching to a second hand t-con board from china. Same thing.
Its my first in depth lcd tv repair. So need to figure out what is wrong? Is it the main board?

[Stigsolbjerg]

Re: Toshiba 48L5463DN no picture, backlight on

Anyone have an idea of what i should mesure to out rule something?
Should i bye a main board, just can't find one from the exact same tv?
Or just give up, since its a vestel, just aint my style!!!

[budm]

Re: Toshiba 48L5463DN no picture, backlight on

Do you have 12VDC at both ends of the SMD fuse on the T-CON board with ref to GND when TV is turned on?

[Stigsolbjerg]

Re: Toshiba 48L5463DN no picture, backlight on

Yep, if you mean the white fuse that has gold ends, 12 volts at both ends. Is there testpoints i should do more mesuring on?

[yokoono]

Re: Toshiba 48L5463DN no picture, backlight on

Vgh (von), vgl(voff) ?.
Unplug the 2 ribbons that lead to the panel one by one and see if a picture appears on a half screen. Do not switch off with the TV on.

[Stigsolbjerg]

Re: Toshiba 48L5463DN no picture, backlight on

Vgh (von), vgl(voff) i dont understand.
I unpluged the two cables one at a time, and i got picture on half the screen, but just on one them.
Vcc_1,2=0,00
Vcc_1,8=0,17
Vcc_3,3=0,98
Vone=0,00
Voffe=0,10
Hvin_12=0,0
Vin_12=12
Havdd=0,0
Avdd=0,0
hope you can use this to outrule some defects? Or is t-con or mainboard ok?

[Stigsolbjerg]

Re: Toshiba 48L5463DN no picture, backlight on

Picture off screen, one cable off.

[yokoono]

Re: Toshiba 48L5463DN no picture, backlight on

Almost all measured voltages are incorrect.
Ex: vcc1-2= 1,2v; vcc1-8= 1.8v ; vcc3-3 = 3,3v ; Vone= aprox. 17v ; Voffe = aprox minus 5v.
Disconnect both ribbons and measure again. Part of the screen on which the image does not appear is defective. As it looks you have problems with the panel. If you are lucky, a smd capacitor may be defective.

[budwich]

Re: Toshiba 48L5463DN no picture, backlight on

Vgh (von), vgl(voff) i dont understand.
I unpluged the two cables one at a time, and i got picture on half the screen, but just on one them.
Vcc_1,2=0,00
Vcc_1,8=0,17
Vcc_3,3=0,98
Vone=0,00
Voffe=0,10
Hvin_12=0,0
Vin_12=12
Havdd=0,0
Avdd=0,0
hope you can use this to outrule some defects? Or is t-con or mainboard ok?

input a better signal into the tv when you do this test (test pattern like smpte color bars or such), post that resulting picture so we can see the result. It is likely that you have some form of panel issue on the side that when plugged in gave no picture. To get around the problem, people use the "tape cutoff method" which involves using a small piece on tape to mask part of the contact pins on the cable going from the tcon to panel on the bad side. It cutoffs of some of the signals going to the side of the panel which has "in panel drivers" that are causing a problem. Once done correctly, your tv and display will probably provide a "good picture".

[Stigsolbjerg]

Re: Toshiba 48L5463DN no picture, backlight on

Godmorning, here are the new results, with both cables to screen disconnected.
Vcc_1,2=1,2
Vcc_1,8=1,8
Vcc_3,3=3,25
Vone=30,9
Voffe=11,35
Hvin_12=11,96
Vin_12=11,96
Havdd=8,36
Avdd=16,43
This must look a hole lot better.
Now you a talking about a bad smd capacitator on the panel board, right?

[Stigsolbjerg]

Re: Toshiba 48L5463DN no picture, backlight on

Now i have mesured the caps on the panelboard, there is six on each panel in groups of two. The side that does not show image, all six is about 28 ohms. The other panel is 10 megaohms and dropping.

[yokoono]

Re: Toshiba 48L5463DN no picture, backlight on

Now we can say that T-con is good. If you connect a ribbon and the voltages disappear there is the problem. Left or right. IF YOU ARE LUCKY a smd capacitor may be in short supply. Most of the time on VONE. Measure the resistance to the table and see what you find.
L.E. You will need to detach the smd capacitors and measure them separately. If they are good there are problems in the panel.

[Stigsolbjerg]

Re: Toshiba 48L5463DN no picture, backlight on

Now i have been doing some mesurements, when i use the Vone testpoints on t-con board to gnd the resitance is25,3 kiloohms with both panels or one of the sides. But with Avdd there is only 24,3 ohms when the left side is plugged in. So where do i go from here? Is it the small components on the panelboard where there is written Avdd?.
What does L.E. mean?

[budm]

Re: Toshiba 48L5463DN no picture, backlight on

Start removing the suspected caps one a time since some of them may be connected in parallel and see if the low resistance reading goes away when the suspect cap/s is removed.
Also show us the pictures of the tab bonding (panel board).

[Stigsolbjerg]

Re: Toshiba 48L5463DN no picture, backlight on

Oh that picture, i did attatch it yesterday but here i try again

[Stigsolbjerg]

Re: Toshiba 48L5463DN no picture, backlight on

Is the suspected caps those in the picture from last post?
Hmm just googled tabs bonding! U mean the three flat cables from panelboard to screen?

[budm]

Re: Toshiba 48L5463DN no picture, backlight on

Tab bonding boards are the long green circuit boards that the LCD's flexible circuit boards are bonded to, as you can see lots of SMD MLCC (Multi Layer Ceramic Capacitor) are on that board in your picture.
So which is/are the caps for the suspected bad caps that show low Ohm readings, the 3 MLCC connected in parallel to the AVDD? If they are then you need to remove one at a time to find out which one is bad.
The designaotrs for those 3 MLCC for the AVDD are CA3, CA2, and CA1

[Stigsolbjerg]

Re: Toshiba 48L5463DN no picture, backlight on

I desoldered this thre components (look at picture), none of them had a resistance near 24 ohms, its more like 1 megaohm and incrising to 20 mohm. And measuring at the Avdd testpoint on the t-con board, there is.still 24 ohms even when the componts is removed from the board.
Now what?

[Stigsolbjerg]

Re: Toshiba 48L5463DN no picture, backlight on

Panelboard nr

[yokoono]

Re: Toshiba 48L5463DN no picture, backlight on

It seems that the defect is in the panel and is irreparable for you. It would be a chance if the panel has side drivers (some "ears" on the edge of the screen).
And if the short is not in the top driver.
Ex.:
https://www.youtube.com/watch?v=YDxghCYcZXA