Sony XBR-52LX900 BL_ERR

[Nicktronic]

Hi all, just curious if the BL_ERR signal is active high or low? TV has the 6 blink error code and I've changed the backlights as they tested questionable (4 strips tested - 203VDC, 203VDC, 203VDC and 175VDC). The new strips all tested at 175VDC. Now when I turn it on, it tries twice to come up and then the 6 blink code. During the this time the BL_ERR pin is high and drops low momentarily, then does it again on the 2nd try to boot (so Im assuming active low). The other thing is the backlight voltage ramps to ~280VDC from around ~160VDC and then back down as the TV tries to boot again. Does anybody know what the backlight voltage is supposed to be on this model?? I think it's low as there's two backlight supplies from the Power Board - one for two strips in series and then the other two.....so based on testing the lights earlier, I would need at least 350VDC to turn them on, right? The caps on the power board are only rated for 350VDC, so that doesn't seem right. I'm confused and hoping somebody can clarify.

I also tried shorting STBY3.3 to Power ON and BL_ON and got a stable ~288VDC out on both outputs to the backlight strips....but they won't light up, like I said I think the voltage is too low. I just can't go higher in voltage as it's reaching the 350VDC threshold of the supply capacitors.

[Diah]

you have the old strips.. calculated the 2 strips which connect together how many LED unit on them if they are direct led BL then ( amount x 3.5V -10 )

[Nicktronic]

Hi Diah, 63 LEDs per strip. 175VDC to turn on one strip (2.8VDC per LED). Two strips in series = 126 LEDs x 2.8VDC = 340VDC.....can't be right!?? Edge LEDs....see attached pics

[Diah]

Hi Diah, 63 LEDs per strip. 175VDC to turn on one strip (2.8VDC per LED). Two strips in series = 126 LEDs x 2.8VDC = 340VDC.....can't be right!?? Edge LEDs....see attached pics

by edge LED BL we always give attention to currents not V. and as yours 4340 type i think you have on each LED there build in protection zener Diode. if this the case. you need to rework and test first the replacement one if there defect zener at some units.. notice TV with out screen in place always turn on and can see the BL turn on..

if they are all fine and the connection between 2 strips are fine too... you can start with checking the currents limit SMD R on the downside of PSU if there one open or changed value from low to high.

BTW. clean yours PSU to avoid spark at parts from top and downside

[Nicktronic]

I think the strips are good, but I can't test two sets in series because of current limitations of my BL tester I guess? Where would I find the current limiting resistor? Can you review the circuit in the picture and give me an idea? OUT 1 is two strips in series and OUT 2 is two strips in series. Thanks.

[Diah]

i asked you to test the original strips LED if there zener diode build in LED

any change value from low to high at these parts will effect the currents.

[Davi.p]

can you watch the sticky post about the photo sizes?

[Nicktronic]

Sure!

[Nicktronic]

Diah, I think there are zener protection diodes on each LED on the old strips. For example, I put 7VDC on one LED and it clamped down to 3.3VDC.

I tested all the SMD resistors and they read good.....except the circled ones in the attached picture. They are 220K, but when measured would slowly increase R from ~150K to 215K.

Thoughts?

[Davi.p]

Hi, need a photo of the solder side of power board, made with much light, not flash, sun light is ok. The resistors are almost surely ok, you are charging a big capacitor so it reads lower..

[Diah]

Diah, I think there are zener protection diodes on each LED on the old strips-----I tested all the SMD resistors and they read good.....except the circled ones in the attached picture.
Thoughts?

i think they are fine.. need to remove out the caps on each rail of them then test them with Ohm
another things. i wrote at my post #4 need to rework. the replacement strips need to be sure 100% all zener of the LEDs are fine. ( tester cant discover this vault ).. just use diode mode on yours DM.they will light dim if yours DM work with 9V battery and when reverse the probe you will have diode reading >7.2mA . after you have this approved all are fine.. then we can working on the currents later. and BL_ON signal include DIMM1 & DIMM2

[Nicktronic]

Alright Diah, you called it! On the old strips in diode mode, 2.5VDC one way, 0.7VDC reverse. On the new strips, 2.5VDC one way, OL reverse!! Damn, this is my problem then yes?

[Diah]

Alright Diah, you called it! On the old strips in diode mode, 2.5VDC one way, 0.7VDC reverse. On the new strips, 2.5VDC one way, OL reverse!! Damn, this is my problem then yes?

exactly this what was thought.... if the replacement defect zener led you could hear peep ton when u used diode mode at DM

[Nicktronic]

Yes, so there is no zener on the LEDs i think because it's all of them. Without the zeners, the backlights won't turn on? Can you explain why exactly?

[Diah]

Yes, so there is no zener on the LEDs i think because it's all of them. Without the zeners, the backlights won't turn on? Can you explain why exactly?

if the LEDs at edge BL with out zener and this not usual.. they will light up depending on V in total .. if there are zener they will light up depending on current A..
if yours orignal LEDs are with zener and the replacement with out.. then this is the issue you have.

[Nicktronic]

Ok, thanks for the information. I'll have to go shopping....

[Nicktronic]

Hi, so I got a new set of BL with zener diode. When I power on the TV:

TCON_12V_GND - 0
TCON_12V_GNS - 0
TCON_VCC_12V - 12.70
TCON_VCC_12V - 12.70

TCON_ON - 3.3
TCON_VCC_12V - 12.70
DIMMER-DC -
DIMMER - 1.5
BL_ON - 2.6.....then goes to 0
BL_ERR - 0.....then goes to 3.3.....then 6x blink code
REG_12 - 12.70
REG_12 - 12.70
REG12_GND - 0
REG12_GND - 0
AUDIO_12V_GND - 0
AUDIO_12V - 12.70
POWER_ON - 3.3
AC_ON_DET - 3.3
STBY3.3 - 3.3

V out to BL is briefly hits about 280VDC then drops to about 111VDC. The backlights never ever light up at all. So maybe whatever is supposed to supply the current isn'?

[Diah]

man you are in hurry, you got other strips... but did you test each LEDf zener if they are fine.... i don't trust things only i test them self to be sure they are fine 100%

[Nicktronic]

Yes, shipping on the new strips was surprisingly fast. I did test them, but not each and every zener. The set came out of broken screen TV that was working. I reeeeeeally don't want to take the TV apart again 😭

Can you help me investigate the power supply board first?

[Diah]

V out to BL is briefly hits about 280VDC then drops to about 111VDC. The backlights never ever light up at all. So maybe whatever is supposed to supply the current isn'?

this is sign of shorted LED... you remember which voltage you have before with out zener... now its correct but it give error

use yours tester and check v on each