Sony XBR75X850C won't power on, no LEDs

[CobrajetMach1]

Hi everyone,

So what happened was that in the middle of watching a movie the screen went completely black. I turned the TV off, then back on but at that point all that happens you can hear a relay click on then back off every 15-20 seconds.

I have tried replacing both the "G2" $ "G4" power supply boards as well as the motherboard and the T-CON board. The replacement boards did come from eBay, however the symptoms are exactly the same after changing them out.

I thought the power supply may be getting a failure protection signal like over current and shutting itself back off so I started removing the output cables from the power supplies one by one. I discovered that when I removed the T-CON 12V connection that the power supply will stay on. At that point I thought for sure it was the T-CON that was bad but like I said after replacing it I have the same issue.

I then removed one of the 4 flat cables from the T-CON to the LCD Panel and then plugged in the AC power. This allowed the power supply to stay on, the backlights come on and stay on and the Sony into sound plays through the speakers.

Does this indicate that the Panel itself is pulling too much current and causing the power supply to trip off? Anything ideas are greatly appreciated.

Thanks

[dskall]

Re: Sony XBR75X850C won't power on, no LEDs

Need good clear straight on pictures of back of tv with cover off and each board. And pictures around ribbon cables to the panel

[CobrajetMach1]

Re: Sony XBR75X850C won't power on, no LEDs

Ok, will do when I get off work.

[budwich]

Re: Sony XBR75X850C won't power on, no LEDs

while you are at it... do your "remove one cable" test with the others to see if it changes what is happening on the screen. Of course, you didn't really specify which cable you played with... hopefully the pictures and further explanation will help. My first guess on the fact you removed a tcon cable and the back lights stayed on and the set made "noise", potentially points to a panel issue.... but further "cable unplugging" tests may help confirm or otherwise.

[bman4]

Re: Sony XBR75X850C won't power on, no LEDs

back light driver or failed leds!

[CobrajetMach1]

Re: Sony XBR75X850C won't power on, no LEDs

Ok here's some pics.
On the T-CON photo the cables I was talking about disconnecting are on the left.

Also there's a small cable that joins the panel boards together. If I disconnect the left or right cable junction and plug in the AC I get the same, backlight and sound, no display though.

[budm]

Re: Sony XBR75X850C won't power on, no LEDs

https://www.badcaps.net/forum/attach...3&d=1500069782
Check the caps on that long tab bonding boards to see any of them show very low resistance or not.

[budwich]

Re: Sony XBR75X850C won't power on, no LEDs

try disconnecting the two on the left (which is the right side of the display). Also try the same for the other side. Is the response of the set different / what happens?

[CobrajetMach1]

Re: Sony XBR75X850C won't power on, no LEDs

Ok, I disconnected the 2 left cables and after connecting the AC all the backlights lit for about 5 seconds then they all went out and after about 5 more seconds they all came back on. Then after about 30 seconds the intro music began to play. The results are the same if I disconnect the right side. I also tried it with all 4 cables disconnected and again the same result.

I tried connecting all 4 back and the original failure symptoms return.
Here's a couple more pics.

[CobrajetMach1]

Re: Sony XBR75X850C won't power on, no LEDs

Reading a dead-short across C01 on the panel board labeled "B_Right"

The panel board labeled "Front_Left" looks like it's the same board, just has everything laid in the other direction. The reference designator is also C01 and I measure 1.85K and 2.25K acrossed it, depending on the meter lead direction.

Maybe tombstone C01 on the "B_Right"?

[budwich]

Re: Sony XBR75X850C won't power on, no LEDs

probably a dumb question, but how do you know if there is no display when you have some of the cables disconnected? I don't know what a sony "splash screen" looks like at start up but does it fill the whole screen or only display a text "piece" of something in part of the screen?

oops... "ships passing in the night"... looks like you may have found your culprit... maybe.

[budm]

Re: Sony XBR75X850C won't power on, no LEDs

Reading a dead-short across C01 on the panel board labeled "B_Right"

The panel board labeled "Front_Left" looks like it's the same board, just has everything laid in the other direction. The reference designator is also C01 and I measure 1.85K and 2.25K acrossed it, depending on the meter lead direction.

Maybe tombstone C01 on the "B_Right"?

It shows <10 Ohms? Remove it and test it off the board also test the empty pads of the cap too after the cap is removed.

[budwich]

Re: Sony XBR75X850C won't power on, no LEDs

Reading a dead-short across C01 on the panel board labeled "B_Right"

The panel board labeled "Front_Left" looks like it's the same board, just has everything laid in the other direction. The reference designator is also C01 and I measure 1.85K and 2.25K acrossed it, depending on the meter lead direction.

Maybe tombstone C01 on the "B_Right"?

can't quite see that on the pictures... but maybe try disconnecting the flex cable connecting the two edge boards on that side and see what happens.

since you have "twin sides" and can compare readings, you have likely found your issue... hopefully.

[CobrajetMach1]

Re: Sony XBR75X850C won't power on, no LEDs

Ok I tombstoned that cap and measured again. It's in parallel with R06 which is a zero ohm resistor. This differs from the "F_Left" which has the zero ohm resistor installed in the component location right next to it and it is not in parallel with C01.

Anyways I removed R06 on the right side and with the short gone I plugged the TV back in and have the same original symptom.

Anyone have schematics?

[budwich]

Re: Sony XBR75X850C won't power on, no LEDs

As suggested, try unplugging the "flex ribbon cable" running between the two edge boards on that side and see what happens.

[CobrajetMach1]

Re: Sony XBR75X850C won't power on, no LEDs

It does the same thing.

[budwich]

Re: Sony XBR75X850C won't power on, no LEDs

Ok here's some pics.
On the T-CON photo the cables I was talking about disconnecting are on the left.

Also there's a small cable that joins the panel boards together. If I disconnect the left or right cable junction and plug in the AC I get the same, backlight and sound, no display though.

did you try doing that for the cable on the other side boards?

[CobrajetMach1]

Re: Sony XBR75X850C won't power on, no LEDs

Yes, did that and also the same thing

[Jdmen]

Re: Sony XBR75X850C won't power on, no LEDs

I think im having the same problem, i got sony xbr65x900c.
It just turned off and no pictures was showing but you can hear the sound.
Then this killer 4 red light blinking comes up, i replaced the TCON board with the exact part number from ebay unfortunately the same issue happens.

Im frustrated coz i only got my tv for a year, any suggestion is greatly appreciated.

I tried to unplug all devices connected to the tv ie; Media Box, HDMI's, Home Theater, LAN cable waited for 5 minutes before turning it ON and still the same problem.

[charlie555]

Re: Sony XBR75X850C won't power on, no LEDs

I just wish I had some blinking lights. Just reboots