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

[Nicktronic]

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

No ripple on the DC. Nothing my DMM could read anyway..

[Nicktronic]

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

wow, thats 5 different DCDC paths all with 12v input. Are you sure all the coils/inductors next to them shows 0V DC on both sides? Sometimes its hard to actually get the probe on the contacts buried on the bottom.

On REG12V, what is AC reading? AC just shows how much noise is above DC. We want to see near 0 for clean stable 12V DC.

Voltages are present....1.1VDC, 1.5VDC, 1.0VDC, 3.3VDC, 5.1VDC. I measured across instead of to GND.

[howardc64]

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

Yes they are very nice! Very easy to do the checks you wanted.

12V A through E have ~12.65 VDC

3 components on REG12V input are good. (no shorts)

wow, thats 5 different DCDC paths all with 12v input. Are you sure all the coils/inductors next to them shows 0V DC on both sides? Sometimes its hard to actually get the probe on the contacts buried on the bottom.

On REG12V, what is AC reading? AC just shows how much noise is above DC. We want to see near 0 for clean stable 12V DC.

[Nicktronic]

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

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

Yes, voltages are present and fuses are good.

[Nicktronic]

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

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

Yes they are very nice! Very easy to do the checks you wanted.

12V A through E have ~12.65 VDC

3 components on REG12V input are good. (no shorts)

[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?

[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

[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?

[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.

[nomoresonys]

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

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

[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.

[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?

[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

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

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.

[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.

[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

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

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.

[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.