Sony XBR-55X900F No picture, no sound no backlight

[Nicktronic]

Hey,

I have this subject TV and when I plug it in I don't get a picture, backlight or sound. The remote and power buttons don't seem to do anything. I've metered the signals on the following after plugging in the TV;

Power Supply Board Connector CN6401 between PSU, MB, TCON

PIN 1 - BL_ERR - 0VDC
PIN 2 - BL-ON - 0VDC
PIN 3 - POWER_ON - 3.47VDC
PIN 4 - N/C
PIN 5 - STANDBY3.3V - 3.50VDC
PIN 6 - N/C
PIN 7 - GND - 0VDC
PIN 8 - GND - 0VDC
PIN 9 - N/C
PIN 10 - REG12 - 12.69VDC
PIN 11 - REG12 - 12.69VDC
PIN 12 - N/C
PIN 13 - REG12 - 12.69VDC
PIN 14 - REG12 - 12.69VDC
PIN 15 - REG12 - 12.69VDC
PIN 16 - REG12 - 12.69VDC
PIN 17 - GND - 0VDC
PIN 18 - GND - 0VDC
PIN 19 - GND - 0VDC
PIN 20 - GND - 0VDC
PIN 21 - N/C
PIN 22 - N/C
PIN 23 - GND - 0VDC
PIN 24 - GND - 0VDC
PIN 25 - N/C
PIN 26 - TCON_ON - 0VDC
PIN 27 - TCON_VCC12 - 0VDC
PIN 28 - TCON_VCC12 - 0VDC

Power Supply Board Connector CN6601 between PSU, LED Driver

PIN 1 - VLED_VCC - 26.04VDC
PIN 2 - VLED_VCC - 26.04VDC
PIN 3 - VLED_VCC - 26.04VDC
PIN 4 - VLED_VCC - 26.04VDC
PIN 5 - N/C
PIN 6 - N/C
PIN 7 - VLED_GND - 0VDC
PIN 8 - VLED_GND - 0VDC
PIN 9 - VLED_GND - 0VDC
PIN 10 - VLED_GND - 0VDC
PIN 11 - SENSE_GND - 0VDC
PIN 12 - BL_CTRL - 0VDC
PIN 13 - N/C
PIN 14 - 12VLD - 12.69VDC

From my limited understanding, the MB has provided the Power On command to the PSU to bring up all supply voltages, but then.....nothing. No backlight command, no tcon command. Safe to say the MB is the issue and to replace it? Is there anything else I should check before I just replace the MB?

I read in another post with similar issues that BGA re-work might be required?

https://www.badcaps.net/forum/showthread.php?t=94067

Has anyone had success with this?

Thanks!

[nomoresonys]

Re: Sony XBR-55X900F No picture, no sound no backlight

There may be several very small fuses on the mainboard, check them for continuity.

[howardc64]

Re: Sony XBR-55X900F No picture, no sound no backlight

Can do a quick check on main's internal power rails

• SPDIF light on?
• USB has power?
• All big inductors on main show some typical voltages? ~1V for CPU. ~1.5 DRAM, ~1.8 + 3.3 eMMC, 5V near USB

I actually have this board from a cracked screen salvage from a couple of years ago. Too bad you are in CA haha ($$$ shipping from US)

[Nicktronic]

Re: Sony XBR-55X900F No picture, no sound no backlight

Can do a quick check on main's internal power rails

• SPDIF light on?
• USB has power?
• All big inductors on main show some typical voltages? ~1V for CPU. ~1.5 DRAM, ~1.8 + 3.3 eMMC, 5V near USB

I actually have this board from a cracked screen salvage from a couple of years ago. Too bad you are in CA haha ($$$ shipping from US)

0V on all circled inductors. 0V at USB. No light on the board at all.

[Nicktronic]

Re: Sony XBR-55X900F No picture, no sound no backlight

There may be several very small fuses on the mainboard, check them for continuity.

I checked as many as i could find and they were good. Gonna take a closer look tomorrow under the microscope at work though.

Also, the big caps in the previous picture all had 12V on them.

[lotas]

Re: Sony XBR-55X900F No picture, no sound no backlight

0V on all circled inductors. 0V at USB. No light on the board at all.

You don't measure voltage there at all, these coils for an audio frequency power amplifier (output for speakers), you need to measure them on these coils.

[nomoresonys]

Re: Sony XBR-55X900F No picture, no sound no backlight

Do you have voltage anywhere on the backlight driver/LD board? maybe check some of the round test points or the little mlc caps, I see you have voltage going to it, wondering if it's getting thru it.

[nomoresonys]

Re: Sony XBR-55X900F No picture, no sound no backlight

Maybe also check the round test pads by the connectors going from LD board to the backlights.

[nomoresonys]

Re: Sony XBR-55X900F No picture, no sound no backlight

Looks like the problem is with 2 BL-ON, and the tcon voltages 26-28.

[nomoresonys]

Re: Sony XBR-55X900F No picture, no sound no backlight

Does the tcon fuse have continuity? and any voltage if you put pos. probe on each end and neg. probe on chassis ground.

[Nicktronic]

Re: Sony XBR-55X900F No picture, no sound no backlight

You don't measure voltage there at all, these coils for an audio frequency power amplifier (output for speakers), you need to measure them on these coils.

0V on all the inductors you indicated.

[Nicktronic]

Re: Sony XBR-55X900F No picture, no sound no backlight

Do you have voltage anywhere on the backlight driver/LD board? maybe check some of the round test points or the little mlc caps, I see you have voltage going to it, wondering if it's getting thru it.

Fuses are good, 26VDC on the caps, very low V (~0.5VDC) on the various test points around the cables leaving the LD board to the backlights.

[Nicktronic]

Re: Sony XBR-55X900F No picture, no sound no backlight

Does the tcon fuse have continuity? and any voltage if you put pos. probe on each end and neg. probe on chassis ground.

T-Con fuse is good, no V on T-Con anywhere.

[Nicktronic]

Re: Sony XBR-55X900F No picture, no sound no backlight

Looks like the problem is with 2 BL-ON, and the tcon voltages 26-28.

Yeah, I think the supplies are good, just the MB is not providing the "turn on" signal for the backlights and tcon right?

[howardc64]

Re: Sony XBR-55X900F No picture, no sound no backlight

0V on all the inductors you indicated.

CPU, RAM, eMMC not powered up so have to see where the PSU's REG12V DCDC conversion to lower voltage path failed. Or can buy main board if confident enough its the failure source.

T-Con fuse is good, no V on T-Con anywhere.

CPU is not running software to tell the T-Con section on main to power up.

Yeah, I think the supplies are good, just the MB is not providing the "turn on" signal for the backlights and tcon right?

CPU is not running so will not issue BL-ON to PSU.

[nomoresonys]

Re: Sony XBR-55X900F No picture, no sound no backlight

Yep, I posted before he tested whole mainboard as pretty much dead.

[nomoresonys]

Re: Sony XBR-55X900F No picture, no sound no backlight

Probably best not to try heating mainboard, I did on my 900c and killed any life that may have been left in it, I may have been able to fix it with patience but after heating it was toast.

[Nicktronic]

Re: Sony XBR-55X900F No picture, no sound no backlight

So, I should find where the REG12 conversion to lower V is happening....or supposed to be happening?

[howardc64]

Re: Sony XBR-55X900F No picture, no sound no backlight

So, I should find where the REG12 conversion to lower V is happening....or supposed to be happening?

Need schematic or some reverse engineering. Luckily I have the exact board in hand haha...

• Traced REG12V to 5x DCDC for reduced voltages. Check voltage at all 5 points labeled 12V-A->E. Probably all 0V.
  
• Check the 3 components between where REG12V comes into main and the GND plane right below it. See if any are shorted.

BTW SONY boards are nice... lots of holes on voltage rails and have exposed copper for easy test

[lotas]

Re: Sony XBR-55X900F No picture, no sound no backlight

0V on all the inductors you indicated.

Is there voltage at all on this connector, are these input fuses intact?