Sony KDL-46S4100 no backlight video or audio - AVS Forum
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Old 08-14-2012, 08:12 PM - Thread Starter
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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.
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Old 09-07-2012, 12:11 AM
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Hi, I have the same problem with my kdl-46s4100. Have you gotten yours fixed? Apparently, there are two versions of mainboard for this same model. You have to make sure that you get the correct one by checking the serial number
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Old 09-07-2012, 05:58 AM - Thread Starter
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Yes there are multiple versions of the board you have to use the serial # on the back plastic panel of your tv to find out which one you need. Mine was a bad main board. the one I ordered from ebay must have been bad as well. Ordered another one from a guy that actually rebuilds them and it worked perfectly. He is on ebay as well. here is a link to his store:

http://www.ebay.com/sch/koshevo/m.html?_nkw=&_armrs=1&_from=&_ipg=&_trksid=p3686

You have to send your old board in as a core.
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Old 09-15-2012, 08:42 AM
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Thank you Jim, I ordered one from eBay n it works again.
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Old 11-02-2013, 09:14 PM
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Hi, Sorry for reacting on the old thread. I'm having the same model, same symptoms and similar voltages on pins as posted by Jim. But I noticed the there is also voltage (-57V) on the two large heat sinks of the G-Board (power board). Is this normal and expected or or is it a sign that G-Board is bad too?

Anyone has a documentation or is willing to measure it for me? Btw mine G-board is 1-857-093-41 and A-Board 1-857-092-41.

 

Based on some thread I did did run a test with CN303 unplugged. With this backlit turned on and screen showed RED-GREEN-BLUE cycle pattern. The voltage on BL-ON pin was something about 5V. Once I plugged CN303 back in the backlit went off.

 

I guess the G-BOARD and Inverter (or Distribution board) are ok since I got the pattern displayed. And I suspect the problem is with A-board. But I do not like that voltage on the heat sinks...

 

Should I order A or G board or both? 

 

I know some people do rebuild these boards. Is there a typical failure point on these boards? I can try to measure ESR on some capacitors but they look visually fine...

Thanks for your help!

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Old 01-02-2014, 07:15 AM
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Did you ever get that kdl-46S4100 working ?  I have the exact same problem, cycle through color bars when I pull the CN303 connector to enable the backlight. TNX

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