Sony Bravia KDL-40W5500 backlight issue

[electroman220]

Re: Sony Bravia KDL-40W5500 backlight issue

You are making the DC measurement in the hot side of the circuit so you have to use the negative leg of the main filter cap as the GND ref for your meter, MAKE SURE NOT TO TOUCH ANYTHING IN THE HOT SIDE WITH YOUR BODY OR YOUR HANDS!

Thank you for the remark!

I did a DC measurement with the (-) led on the negative leg of capacitor C6501 and (+) led on one of the legs of fusible resistor R6500. Both read 389V DC when the tv is turned on (green indicator led). To be able to perform the measurement, I needed to disconnect the inverter board.

Have you visually inspected under the powerboard? In particular, check under the transformer (top left in pic 1) to see if there's any cracked soldering.

I inspected it and everything looks very proper to me.

[electroman220]

Re: Sony Bravia KDL-40W5500 backlight issue

Anyone?

[electroman220]

Re: Sony Bravia KDL-40W5500 backlight issue

Someone willing to provide help? Would be appreciated very much!

[dick_barton]

Re: Sony Bravia KDL-40W5500 backlight issue

What voltages do you have at the connector?

[electroman220]

Re: Sony Bravia KDL-40W5500 backlight issue

I did the following DC measurements for connector CN6154 (connection with logic board):

* NC: 0V
* DIMMER: 0V
* BACK_LIGHT_ON: 2V
* INV_ERROR: 0V
* GND: 0V
* BALANCER_ERR: 0V

But some values change 3 times for a few seconds, the third time the tv shuts down and the led starts blinking red 6 times. When the values change you can also hear some kind of "buzz" sound. Each time the values change to:

* NC: 2.5-3V
* DIMMER: 2.5-3V
* BACK_LIGHT_ON: 0-0.5V
* INV_ERROR: 0V
* GND: 0V
* BALANCER_ERR: 0V

[dick_barton]

Re: Sony Bravia KDL-40W5500 backlight issue

In your first post you said:-

CN6701 connector (to balancer board):
* 12VCC
* FB
* FB
* LD
* LD
All these read 0V DC.

Did you also mean that the 12V pin was also 0V when you measured it?

All the other voltages you have provided appear to be OK.
Do the backlights flash when you first turn the set on because at that time the backlight control signal is switched on.

When the red led is flashing do the voltages at CN6701 change?

Can you post a photo of your inverter board

[electroman220]

Re: Sony Bravia KDL-40W5500 backlight issue

In your first post you said:-

Did you also mean that the 12V pin was also 0V when you measured it?

Yes, that is correct.

All the other voltages you have provided appear to be OK.
Do the backlights flash when you first turn the set on because at that time the backlight control signal is switched on.

No, the screen remains pitch black.

When the red led is flashing do the voltages at CN6701 change?

No, they stay at the same values as when the green led is on.

Can you post a photo of your inverter board

See attachement: because the board is so large, I took a picture for both the lower and upper part.

[dick_barton]

Re: Sony Bravia KDL-40W5500 backlight issue

OK, so it appears that your problem is that no 12V supply to the inverter board.
If you unplug CN6701 and measure the 12V line again and see if it is there. It may be loaded down by the inverter.


Edit
It should be there because you also quoted CN6150 as having 3 x 12V outputs and the 12V supply to the inverter should come from the same generated 12V supply that feed them. It may be worth checking to see if you have any 0 ohm resistors which may have gone open circuit on the underside of the power supply pcb.