SONY KDL-55HX850 : No backlight, no error code, rest OK

[Jojo337]

Hi all !

I got a Sony 55HX850 with psu APS-326(ch) and Driver LED ST550RD-S01.
I don't know what happenned before I get it.

The TV is working great, except the led backlight that does'nt. Backlight nevers turn on, not even a little flash.

The TV doesn't show red light errors at start The tv is working, I heard the sound of TV from antenna, menu etc... with the flash of my phone I can see the picture that seems fine (T-con OK ?).

Fuses from Driver LED ST550RD-S01 seems fine (multimeter beeping : not broken, 0V), and caps of this card too.

Pins :

If I disconnect the Driver LED cable (CN6601), nothing changes :
CN6601 pins (tested on card and psu):
TV ON :
Pin 14 : 3.3v
13 : 3.8v
12 : 0.6v
11 : 0.7v
Others : 0v

TV OFF
Pin 11 : 0.7v
Others : 0v

TV STARTING
Like ON
BUT ALL VLED_VCC (pins 1 2 3 4) go to 0.15v and go back to 0v after 4 seconds.

If I disconnect CN6401 (to the motherboard), no backlight.
If I disconnect any other cable, the error leds associated to what I disconnected appears.

CN6401 (to motherboard) pins :
TV ON : TV OFF :
Pin Pin
28 3.3v 28 3.3v
27 3v 27 3v
26 3.3v 26 0v

23 3.3v 23 3.3v

20 12.43v 20 0v
19 12.43v 19 0v
18 12.53v 18 12.54v
17 12.53v 17 12.54v
16 12.53v 16 12.54v
15 12.53v 15 12.54v
14 12.53v 14 12.54v
13 12.53v 13 12.54v
Others : 0v Others : 0v

OOF long post !! So anyway I'm in France and ... voila !
(I tried a shunt pin 5/23/28 but nothing).

Thanks for the help ! Have a good day.

[Diah]

Re: SONY KDL-55HX850 : No backlight, no error code, rest OK

CN6401 pin 5 BL_ON did you have voltage on it when turn on ?

[Jojo337]

Re: SONY KDL-55HX850 : No backlight, no error code, rest OK

I tested this pin and no, always 0V.
I tried to do a shunt with POWER_ON and STBY_3.3V but nothing happens with the TV too !

[Diah]

Re: SONY KDL-55HX850 : No backlight, no error code, rest OK

I tested this pin and no, always 0V.
I tried to do a shunt with POWER_ON and STBY_3.3V but nothing happens with the TV too !

disconnect the cable of pins 5 BL-ON from the socket on PSU .. jumper pin 5 with standBy pins via R1K 1/4W or less. then turn on the tv see if BL come on

[Jojo337]

Re: SONY KDL-55HX850 : No backlight, no error code, rest OK

disconnect the cable of pins 5 BL-ON from the socket on PSU .. jumper pin 5 with standBy pins via R1K 1/4W or less. then turn on the tv see if BL come on

Ok I just ordered some resistors 1kohm 0.25w I will come back when the test will be done ! Thanks

[Jojo337]

Re: SONY KDL-55HX850 : No backlight, no error code, rest OK

Hi ! So the backlight with the resistor between pin 5 (PSU) and with standby 3.3 doesn't turn on Do you have other ideas ?

Thanks !

[nomoresonys]

Re: SONY KDL-55HX850 : No backlight, no error code, rest OK

Not sure how you did it, try UNHOOK cable from powerboard to mainboard leave it off, take one resistor from pin 5 to 3.3 standby and another from pin 28 to the same 3.3 standby, plug power into powerboard, see if the backlights come on and stay on.

[Jojo337]

Re: SONY KDL-55HX850 : No backlight, no error code, rest OK

I inserted the resistor into pin 23 (in addition with original "pin 23, or connector" from cable, detached the connector "pin 3" from the cable and inserted the second pin of the resistor into pin 3 of the PSU. I got 3.3v in the resistor "pin".

I will try this tomorrow, thanks

[nomoresonys]

Re: SONY KDL-55HX850 : No backlight, no error code, rest OK

Remember with test in post #7 you unhook the whole cable, don't want to accidentally fry anything.

[Jojo337]

Re: SONY KDL-55HX850 : No backlight, no error code, rest OK

Yes, nothin plugged except the "Driver led" cable and the modifications.
So after the #7 post test, nothing happens. I heard the "clac" from the PSU, but no backlight.

BL_ON is at 3.3v with resistors but no backlight.

After the tests, unsoldering the resistors, the tv is like before (turns on, screen and sound OK but no BL).

https://img.super-h.fr/images/c4345e...39bd8905c8.jpg
(Ok this looks bad, but the picture is after testing and after removing protection between pins/solder points with tape )

[nomoresonys]

Re: SONY KDL-55HX850 : No backlight, no error code, rest OK

Try this, see the one from 23 to 28? take it off at 23 and hook it to 5 and leave the rest the same.

[Jojo337]

Re: SONY KDL-55HX850 : No backlight, no error code, rest OK

There was a mistake in my post #8, it's the pin 5 and not the pin 3.

Anyways, pins 28 to 5 with resistor and 5 to 23 with resistor does the same !

[nomoresonys]

Re: SONY KDL-55HX850 : No backlight, no error code, rest OK

Ok, my bad 23 is standby, you may need an additional resistor from pin 2 to 23 also to go along with the other two resistors, so 3 resistors used, so 3 resistors will be on 23 and the other ends will be on pins 2, 5 and 28.

[Jojo337]

Re: SONY KDL-55HX850 : No backlight, no error code, rest OK

Still nothing with the 3 resistors (STBY3.3, POWER ON, BL_ON and PWM_DIMMER), same reactions (pins are 3.3v)

[budm]

Re: SONY KDL-55HX850 : No backlight, no error code, rest OK

Your post #1:
If I disconnect the Driver LED cable (CN6601), nothing changes :
CN6601 pins (tested on card and psu):
TV ON :
Pin 14 : 3.3v
13 : 3.8v
12 : 0.6v
11 : 0.7v
Others : 0v

CN6601 per chart on your post #1 Pin 14 is the LED ON (BL-ON) and you do have 3.3V there on pin 14.

Since you do not have VLED_VCC for driving the LED driver board, the power supply feeding the VLED needs to be checked.

Check fusible resistor R6547.

I also need good clear straight shots pictures of the whole top and bottom side of YOUR power supply board, and also the pictures of the whole backside of the TV showing how all the boards are connected together.
Please also upload the service manual since you already have it.

Pictures provided by shopjimmy.
APS-326(ch)_Sony 1-474-385-11 G7 PS

[Jojo337]

Re: SONY KDL-55HX850 : No backlight, no error code, rest OK

Hi and thanks you for your help !

To be clear, when all cables are connected, BL_ON (CN6401 to main borad) is never 3.3v, even if LED_ON (CN 6601 to driver LED) is ~3.28v.

R6547 : Beeping with tester (continuity), 0.001v, 018.5 ohm in multimeter (18,5 ohm so ?), it's written 0.1 ohm on it, is it broken or my test is wrong ??

Service manual too big for attachment :

[Diah]

Re: SONY KDL-55HX850 : No backlight, no error code, rest OK

Hi and thanks you for your help !

To be clear, when all cables are connected, BL_ON (CN6401 to main borad) is never 3.3v, even if LED_ON (CN 6601 to driver LED) is ~3.28v.

check the Fuse on LED driver boards F2001. if its okay.. ready for risky job to take screen apart. search for other 2 hands help you with this risky job.

[budm]

Re: SONY KDL-55HX850 : No backlight, no error code, rest OK

Hi and thanks you for your help !

To be clear, when all cables are connected, BL_ON (CN6401 to main borad) is never 3.3v, even if LED_ON (CN 6601 to driver LED) is ~3.28v.

R6547 : Beeping with tester (continuity), 0.001v, 018.5 ohm in multimeter (18,5 ohm so ?), it's written 0.1 ohm on it, is it broken or my test is wrong ??

Service manual too big for attachment :

1) Monitor that LED_ON pin of CN6601,it should change state between <1V and > 3V when you turn the TV on and off.

2) Set meter to 200VDC scale, Keep black meter probe on chassis, red probe any one of the any one of the VLED_VCC pin of the CN6601 then turn on the TV while watching the meter to see if you see the Voltage jumps up at all.

[Jojo337]

Re: SONY KDL-55HX850 : No backlight, no error code, rest OK

Hi !

check the Fuse on LED driver boards F2001. if its okay.. ready for risky job to take screen apart. search for other 2 hands help you with this risky job.

F2001 : Continuity OK (beeping), 0.001v, 0 ohm

1) Monitor that LED_ON pin of CN6601,it should change state between <1V and > 3V when you turn the TV on and off.

2) Set meter to 200VDC scale, Keep black meter probe on chassis, red probe any one of the any one of the VLED_VCC pin of the CN6601 then turn on the TV while watching the meter to see if you see the Voltage jumps up at all.

1) LED_ON is ~-0v in standby and 3.28v TV on

2) VLED_VCC are 0v in standby, go up to 0.140v EACH 4 VLED_VCC for 2 secs and go down to 0V 3 sec later progessively.

Thanks again !

[budm]

Re: SONY KDL-55HX850 : No backlight, no error code, rest OK

Hi !


F2001 : Continuity OK (beeping), 0.001v, 0 ohm



1) LED_ON is ~-0v in standby and 3.28v TV on

2) VLED_VCC are 0v in standby, go up to 0.140v EACH 4 VLED_VCC for 2 secs and go down to 0V 3 sec later progessively.

Thanks again !

1) So BL_ON (LED_ON) control signal is fine.

2) So the LED power supply does not even try to put out anything, I would look into that power supply section, since we do not have the schematic of the power supply, then it will have to be traced out, the SMPS IC for that section need to be checked to see if it is getting VCC to run or not, etc.