Sony KDL-46S4100 No Backlight Video or Audio

[budro]

I have a Sony KDL-46S4100 that the backlight will not come on. Power light turns on steady no flashing. Even with a source plugged in you cannot get the input to switch to it to turn on the screen. If I disconnect connector CN303 I get the Blue, Red, Green test pattern. So I know the inverter board, panel and backlight work. I tried a different main or A board and had the same results they both have the exact numbers just different serial's at the bottom. Tested the fuse on the T-con board and getting power through it. Here are the voltages I am getting at the power supply connectors:

Powered ON:

CN301
1-15.71v
2-15.71v
3-0v
4-0v
5-7.18v
6-0.01v
7-3.44v
8-3.44v
9-3.43v
10-0.01v
11-0.01v
12-0.01v
13-11.60v
14-0.00v

CN301 Powered Off:all are 0.00v except pins 2,7,8,9 these are 0.05v

CN302 Powered on Powered off
1-0.00v 1-0.00v
2-0.00v 2-0.00v
3-3.28v 3-3.29v
4-3.28v 4-3.29v
5-0.00v 5-0.00v
6-0.00v 6-0.00v
7-0.02v 7-3.28v

CN303 powered on Powered off
1-0.00v 1-3.25v
2-0.17v 2-0.06v
3-N/C 3-N/C
4-1.69v 4-0.22v
5-0.00v 5-0.00v

I know pins 1 on CN303, 1 on CN302, & 7 on NC302 are all low voltage or 0volts which control the backlight circuits. My question is do these voltages come from the power supply or are they returned to the power supply board from the main or A board?
Any help would be greatly appreciated. I have ordered a power supply but wanted some others opinions as well.

[selldoor]

Re: Sony KDL-46S4100 No Backlight Video or Audio

Hi - we can do little without pictures of your boards even with your good description I have no idea where C301 goes from/to. As the test screen works
it suggests problem with the main board rather than the power supply.
Welcome to the forum-
We can help a lot more if you please post a good clear pictures of the whole chassis and wires, and then pictures of each board, front and back and close up of connectors, (max resolution 2000x2000 and 2MB) using the manage attachments button, which is found by clicking "go advanced" under quick reply.

Please do not post inline and offsite as they slow down the loading of pages.

Examples of what is needed
https://www.badcaps.net/forum/attach...1&d=1290283049

https://www.badcaps.net/forum/attach...7&d=1280167246

[budro]

Re: Sony KDL-46S4100 No Backlight Video or Audio

All 3 of the connectors I measured go to and from the powersupply and main board. CN301 is in the upper right corner of the power supply, CN302 and CN303 right under it. I have uploaded the pics of the chassis, main board (green one on the right with all the jacks) and power supply (yellowish orange board)

[Rudy.ALvarez91586]

Re: Sony KDL-46S4100 No Backlight Video or Audio

I unplugged my cn303 and i didnt' get a test screen so which is the inverter board i have the same problem on my tv

[budro]

Re: Sony KDL-46S4100 No Backlight Video or Audio

My problem was in fact a bad main board. I got another one and it worked flawlessly. If your backlight doesnt come on at all I would look at your voltages on the power supply first. As far as the inverter board it is the board at the far left of your tv looking at the back of it. Have you tried using a flashlight and seeing if you see any thing on the screen? If you dont see anything at all it may be more than just the inverter board.

[budm]

Re: Sony KDL-46S4100 No Backlight Video or Audio

The long board on the far left is not really inverter board, SONY called it Balancer board because the inverter board is part of the power supply board (it is inverter/power supply combo board) as you can see the high voltage transformer on the top left, the Balancer board receives the high voltage and distribute it to each lamps.

[Rudy.ALvarez91586]

Re: Sony KDL-46S4100 No Backlight Video or Audio

okay well i did the voltage readings I had all about the same readings as budro except for Pin 4 on cn303 read .002v instead of .22v when powered off

[Rudy.ALvarez91586]

Re: Sony KDL-46S4100 No Backlight Video or Audio

I also put a flashlight to it there is absolutely nothing on the screen that i can see as far as the serial number to the boards that i might need i get those off the barcode sticker on yellow board and the barcode sticker on the cover of the green board right