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Old 12-01-2017, 04:25 PM   #1
freakaftr8
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Default Sony XBR75X850C no picture backlights on

Received this from somebody and this is an interesting one.
By mishal symptoms were no picture no backlight and a flashing Amber and green light upon start up . Read up on the Internet about Sony and forced usb updates.

. So I did that And now I get back lights but still no picture. Upon inspection I notice that some of the voltage regulators and inductor coils are not putting out voltage on tcon. It would appear that as soon as I disconnect one of the 4 flat ribbons into the panel from the T con I lose my 3.3 volt . Is this some kind of a passive system where all cables need to be connected to create a closed loop circuit back to the feedback system of the tcon? I can only speculate that either this is a failure of the tcon board or panel.

All of the other posts I have seen on this forum in regards to this particular model that uses a Samsung 4K LCD panel point to panel fault.

So basically I'm wondering if for any reason something is not jiving with the LCD panel like a short circuit somewhere upon a ribbon driver it will not allow the tcon to initiate the primary voltages to drive the COF and FRC drivers

I have noticed that there are for M LCC capacitors on the far left of the tcon that seem to go short when the far right ribbon is connected to the tcon from the panel But there is no inherent difference between having all connected or one connected. Still the left side of the tcon seems to have completely dead voltages.

The only voltages I have notice being supplied to the panel are the 1.8 and 3.3 v. I believe there is a 17 v or something along those lines it supposed to also be applied and that's missing
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Old 12-01-2017, 05:34 PM   #2
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Default Re: Sony XBR75X850C no picture backlights on

Here's pics. CSA6 thru CSA9 go short with far right ribbon to panel attached. Without it attached about 1.6k ohm.
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File Type: jpg 20171201_163312.jpg (773.4 KB, 42 views)
File Type: jpg 20171201_163322.jpg (722.2 KB, 30 views)

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Old 12-01-2017, 05:53 PM   #3
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Default Re: Sony XBR75X850C no picture backlights on

check for the components at the lower edge boards on that side. :-)
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Old 12-01-2017, 06:11 PM   #4
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Default Re: Sony XBR75X850C no picture backlights on

That's what I was thinking. But I would at least assume that possibility of voltages coming up from the tcon with panel disconnected maybe this is a closed loop system
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Old 12-03-2017, 02:59 PM   #5
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Default Re: Sony XBR75X850C no picture backlights on

Ok. More research shows if you power up tv w/o tcon connected, automatic flashing green and amber status light. Meaning eeprom lost panel ID configuration. Weird system..this requires a sub update every time. Going blind update Because you will not see what is happening on the screen because it's completely dead even back lights are out and no 12v to tcon. After about an hour the update will finish in allow the back lights to come on in supply 12 V to tcon. This will happen every time you disconnect the tcon in power up the TV
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Old 12-03-2017, 03:56 PM   #6
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Default Re: Sony XBR75X850C no picture backlights on

Mad stuff

Looks like u will have to hunt down shorted caps on the sub board connected to the lcd panel.
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Old 12-03-2017, 06:44 PM   #7
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Default Re: Sony XBR75X850C no picture backlights on

Well you guys are right as soon as I plug in the far right cable to the panel I immediately get a short circuit across the four M LCC capacitors off the DC converter shown in the previous pic . What I did is I covered up with tape the 16 V drive on the right side. I immediately noticed the short was gone upon inspection of testing on the MLCC's. Then powered up suddenly I noticed all tcon voltages came back and I have a perfect left side but dead right side. So I was correct this system requires a full loop back between left to right in order to power up tcon voltages. With the data drive going to the full left and right side of the panel you can disconnect the VCC to either side and you will still get a picture. Only if all data drive output signals and feedbacks are registered being connected it will allow the T con to do a full power up regard less if one or other side 16 V VCC is connected or not

Unfortunately chock this one up to a shorted panel. What a shame. Such a nice Sony 75 inch 4k too
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Old 12-03-2017, 08:08 PM   #8
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Default Re: Sony XBR75X850C no picture backlights on

The white blob is just background
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Old 12-04-2017, 06:16 AM   #9
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Default Re: Sony XBR75X850C no picture backlights on

but is there any corner cables on this panel that you can also disconnect?
Have you "inspected" the bottom edge boards on that side to see if you can find any issue?
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Old 12-08-2017, 01:12 AM   #10
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Default Re: Sony XBR75X850C no picture backlights on

OK got into this thing further and found a shorted M LCC capacitor at location CSA191. This runs the 1st ribbon driver on 4th board over on FRC. Replaced shorted M LCC and short when a way that was showing up on the tcon. However upon powering up I still have no picture some of the low voltages like the 16 volt and others do not want to come up on tcon. I cannot seem to get them to come up even thou the old board for some reason I had to heat up in order for the voltages to come up to show the good side of the panel working. Received new tcon a and same issue. Panel is manufactured by Samsung and so is the tcon board. My question is do all ribbon connections need to be made in order for a loopback feedback back to the tcon to power up other voltages? As anyone ever heard of this in case I might still have some problem with the LCD panel even know everything seems to test good going back to tcon board now.

Only voltage present is 1.3v running main processor. VCOM ,VCC, VREF, AVDD, HVDD, And all other voltages dead.

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Old 12-08-2017, 03:24 AM   #11
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Default Re: Sony XBR75X850C no picture backlights on

Wow.. a giant 75 inches for free, you lucky! But you must pay body building lessons to handle it...

Unfortunately i dont understand all your text due to my english, maybe are you using some slang? The only thing i can understand and suggest you is to get a switching psu and supply externally to the panel with tcon unhooked a 15-16v to the AVDD lines or if you don't have such a psu try at least with a common 12v and see what happens, is the fastest way to show for a short, if the PSU goes in to protection then you have a short on that line, rather.. if the psu is not shortcirc. protected is even better so you see which part is broken by touching what gets very hot or start to smoke. I have good news for you, tcon smps can go short also only at full charge, so there's a remote possibility your tcon is faulty and even the replacement one..(but difficult i think).

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Old 12-08-2017, 08:53 AM   #12
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Default Re: Sony XBR75X850C no picture backlights on

Yes good information. I was thinking about externally powering the 16v line to see what happens as well.
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Old 12-08-2017, 08:56 AM   #13
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Default Re: Sony XBR75X850C no picture backlights on

But is my theory correct That some tcon boards need to have a fully integrated input and output feedback to the tcon in order to power up all voltages? It's just nothing that I have seen before period usually supplying an external signal of 12 votes to AT con will allow all voltages to come up whether the panel is connected or not. These 2 boards that I have now will not allow any voltages to come up with just 12 votes connected and no panel.
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Old 12-08-2017, 10:33 AM   #14
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Default Re: Sony XBR75X850C no picture backlights on

What is the LCD panel model number?
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Old 12-08-2017, 11:11 AM   #15
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Default Re: Sony XBR75X850C no picture backlights on

I've never seen any feedback from the panel sorry, but i'm here lucubrating but whithout a good picture of the tcon unhooked and with direct sunlight and hires, is difficult.. 16v is not VCC but AVDD, and is the Drain voltage of pixels, so i think is difficult is in short with anything apart some caps on the long pcbs, lets see to what are connected those 4 caps in short.. bye..

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Old 12-08-2017, 11:32 AM   #16
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Default Re: Sony XBR75X850C no picture backlights on

The four caps are the VCC output on the tcon. Of course now that I removed the short still no outputs on tcon. With old tcon I covered up the VCC output on the right panel ribbon and was able to achieve voltages and half a picture only after I heated up the tcon around the DC converter IC.

I'm not sure of panel model but I'll find out later when I get home.

The VCC is what was shorted on right side of panel.

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Old 12-09-2017, 12:43 AM   #17
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Default Re: Sony XBR75X850C no picture backlights on

Ok. Panel model
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File Type: jpg 20171208_234144.jpg (442.7 KB, 15 views)

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Old 12-09-2017, 12:53 AM   #18
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Default Re: Sony XBR75X850C no picture backlights on

Sorry for the upside down pic
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Old 12-09-2017, 01:07 AM   #19
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Default Re: Sony XBR75X850C no picture backlights on

Ok i have give you an idea, now why don't you power supply this panel as i've said? I suggest you obviously to solder wires on panel's board to supply, not use flat cables that can burn..

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Old 12-09-2017, 01:33 AM   #20
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Default Re: Sony XBR75X850C no picture backlights on

The HVDD btw was the area shorted on the right side originally. On FRC board. This is the voltage drive for the column drivers. One capacitor was shorted like I mentioned previously.

I just never seen a tcon that won't produce voltage if panel left disconnected. That is if what is really happening here if I didn't receive another defective tcon.
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