Hisense RG50 PSU board RSAG7.820.8364 with solid red light

[c_corr]

I am trying to repair a 50 inch Hisense RG50 model TV that has solid red light when connected to power point and no change when attempting to power on the TV from hardware button.
Backlight does not come on and no image on LCD screen when checking with a flashlight.

This RG50 tv has next boards in it:
- PSU board number: RSAG7.820.8364.
Found no close schematoic for it. After cleaning the annoying Conformal Coating from the ICs I found it uses IDP2303 for PFC and the 3 voltages 12V, 16V and some 40V used for backlight (40V supposed to be 60V).
Also uses IW7027 QFP IC (manufactured by Dialog) located on the little green PCB module for LED strips drivining.
RSAG7.820.8349 has a part of schematic that uses IDP2303 IC but outputs 200V for backlight instead of 60V.
This PSU drives 16 strips of LEDs.
- Main board number: RSAG7.820.8269

I have tested the 16 LED strips with an Aliexpress backlight LED tester (29mA contant current)- all 16 strips have 44V in direct conduction (I see them lighting up) and 9V when tested in reverse.
I found the mainboard outputs 3.3V to the STB pin of the PSU but zero volts to PSU BSW pin that is supposed to turn on the backlight LEDs.

I used a jig made of 2xAAA batteries to test if PFC works and when applying 3.3v on PSU STB pin I see the voltage going from 320V to 380V on the caps. Also 9V standby voltage goes to 12V and the other voltage goes from 12V in standby to 18V.

With PSU disconencted frrom mainboard -> I aplied 3.3v on both STB and BSW pins but backlight voltage does not go over 40V - also I cannot see any LED strip lighting up.

My understanding is that with 3.3v on both STB and BSW pins the backlight LED strips were supposed to light up. Unless it needs some continus 3.3v voltage or 3.3v TTL pwm signal applied on PSU PWM pin too to turn on the backlight?
PSU does not seem to work as it should.
I confirmed that the voltage regulator LM117 3.3v on the LED drive QFP IC boatrd works ok and outputs the 3.3v.
Trying to find if the problem is in mainboard or in the PSU. Mainboard CPU feels slightly warm after power applied to mainboard for 5 min or more.

I uploaded some PSU pics

[lotas]

First, check the backlight. Hisense has backlight protection. If the backlight is not working, the TV will not switch to operating mode.

[c_corr]

Thank you. Checking closer the backlight drive I found this PSU RSAG7.820.8364 board uses IW7027 QFP IC as pure LED driver and AP3041 IC as voltage boost controller for LED driver.
Backlight voltage sits at around 30V in standby then goes to 40V when PSU board STB and BSW pins activated with 3.3v but voltage but never goes close to 60V. It is possible this AP3041 may not work to boost the voltage used for LEDs and its "flag" pin signal may disable the LED driver too.
The only schematic with AP3041 is in IC datasheet could not find any Hisense PSU schematic with it.

[lotas]

Hisense RSAG7.820.8307 (AT3041)

[lotas]

K-PL-L03 (AT3041)

[Diah]

there are no Protection at this model , its Roku TV based on Google / Android OS, yours 3.3V to test the PSU was not complete because you ignored the other Socket of LED SCL for BL Zon
, Steady Red LED mean always no reaction from SW, check if you do have 5VCC on USB Port then play software to see if the condition changed, at least there are Monitor circuit at the SoC to watch GPU if the panel an issue had, will keep the SW / System silent, as well 50 Size Panel known all of them bad.. it could be the issue there too

[lotas]

Whether there is protection or not, what does the operating system have to do with it if the protection is installed on a component basis in the LED driver itself?

[Diah]

this Flag to cut off LED VCC Rail only, MB / SW should work with out BL

[c_corr]

Thank you for the schematics and sugegstions.
This is how the two connectors signnal pins look on the PSU board.
AP3041 ic seems to need at least 3.3v on the PWM pin. It is unclear if PWM pin has pull up inside the AP3041 - I will measure the voltage on this pin and try to apply some 3.3-5.0 DC DC voltage on it via some series resistor.
Will experiment more once i install back the LED drive board module on the PSU board. Plan to supply 12V to that LED driver module board and measure few voltages ->iW7027 has a 5Vcc exit on pin 2 (5VDD).