Hi Respected forum members,
I have trying to resolve a Samsung TV MODEL-UA40K5000ARLXL multiple issue since last 1.5 months, but now i am stuck having tried almost everything as per my limited knowledge, and hence I seek you support.
Issue : The TV turned off automatically one day.
No Backlight ,No image on screen(flashlight test done),no standby
Samsung repair technician could not find the fault and asked to replace the PSU board, which my ego did not agree with
The Board is L40MSFN-FHS BN44-00851B.
I have searched the whole internet and haven't been able to find the circuit diagram from last 1.5 months.
Diagnostic Steps taken by me :
I opened the TV after watching several YouTube videos for common faults with LCD/LED Tv's and how to fix them.
1.I checked voltages in the Hot section till high voltage capacitors and the voltages are between 325 to 345volts DC after bridge rectifier.
Fuse was okay too.
However the secondary side (Cold side) one schottky Diode was found shorted .( I thought I found the common fault and could fix easily)
While proceeding with multimeter checks, I might have shorted the board somewhere , then the fuse went out.
2.I misread the fuse number and replaced with 10 amps normal fuse as opposed to 3.15 amps ceramic one (its not easy to find components in India ,even with full specs) ,next when plugged in AC mains , the thermistor blew up.
I was scared but not done yet.
3.I increased my knowledge about the primary circuit and learned function of each and every component .
Finally I found the MOSFET to be shorted on primary side .
I searched for proper components in local market as per original component data sheets ,then replaced equivalent values Fuse ,MOSFET & Thermistor on primary side & schottky diode on secondary side.(image 1 -InkedSamsung PSU1 attached)
4.Once Again the voltages were reaching the capacitors but not beyond .
I suspected the PWN IC to be bad which switches the MOSFET on/off to start the main transformer ,After searching more on internet ,I found a post which explained how to check PWM IC 3S111 and found the PWM IC was the issue and replaced with original(Image 2-InkedSamsung PSU2) and yes I was able to bring the TV back to life .
Partial problem solved :The Standby came on , sound came on , image came on BUT NO backlight.
5.I once again searched internet and then opened by full TV to check the LED strips to my surprise each LED checked individually was lighting up, since i didn't have bench power supply to check full strips .(Dis-Assembling & Assembling TV took 6 pain full hours)
Plugged again in AC main the TV still runs with image & sound but no backlight.
Help required :Now I think the LED driver IC maybe at fault but again i have no schematics as there is nothing written on the chip ,no matter what magnification level I use, its blank.(Image 3-InkedSamsung PSU3 attached)
I have checked the MOSFET for LED circuit ,that is not shorted but When after switching off the TV ,I put Multimeter red probe to "Drain" and "black probe" to "Gate" terminals the LED strips light up for a short time. That proves its working.
Additionally I have also checked that it's not the main board at fault ,but PSW itself(Check method -Switch on TV with everything plugged in ,then disconnect the main board cable, if led lights up the issue with main board , if not PSU fault ).
Fault code :Now after switching on tv, Standby LED blinks 3 times,Sound okay ,image okay
Any help next steps will be highly appreciated.
Let me know if you need specific voltage checks at connectors , I can capture an send.
Thank you in advance
I have trying to resolve a Samsung TV MODEL-UA40K5000ARLXL multiple issue since last 1.5 months, but now i am stuck having tried almost everything as per my limited knowledge, and hence I seek you support.
Issue : The TV turned off automatically one day.
No Backlight ,No image on screen(flashlight test done),no standby
Samsung repair technician could not find the fault and asked to replace the PSU board, which my ego did not agree with
The Board is L40MSFN-FHS BN44-00851B.
I have searched the whole internet and haven't been able to find the circuit diagram from last 1.5 months.
Diagnostic Steps taken by me :
I opened the TV after watching several YouTube videos for common faults with LCD/LED Tv's and how to fix them.
1.I checked voltages in the Hot section till high voltage capacitors and the voltages are between 325 to 345volts DC after bridge rectifier.
Fuse was okay too.
However the secondary side (Cold side) one schottky Diode was found shorted .( I thought I found the common fault and could fix easily)
While proceeding with multimeter checks, I might have shorted the board somewhere , then the fuse went out.
2.I misread the fuse number and replaced with 10 amps normal fuse as opposed to 3.15 amps ceramic one (its not easy to find components in India ,even with full specs) ,next when plugged in AC mains , the thermistor blew up.
I was scared but not done yet.
3.I increased my knowledge about the primary circuit and learned function of each and every component .
Finally I found the MOSFET to be shorted on primary side .
I searched for proper components in local market as per original component data sheets ,then replaced equivalent values Fuse ,MOSFET & Thermistor on primary side & schottky diode on secondary side.(image 1 -InkedSamsung PSU1 attached)
4.Once Again the voltages were reaching the capacitors but not beyond .
I suspected the PWN IC to be bad which switches the MOSFET on/off to start the main transformer ,After searching more on internet ,I found a post which explained how to check PWM IC 3S111 and found the PWM IC was the issue and replaced with original(Image 2-InkedSamsung PSU2) and yes I was able to bring the TV back to life .
Partial problem solved :The Standby came on , sound came on , image came on BUT NO backlight.
5.I once again searched internet and then opened by full TV to check the LED strips to my surprise each LED checked individually was lighting up, since i didn't have bench power supply to check full strips .(Dis-Assembling & Assembling TV took 6 pain full hours)
Plugged again in AC main the TV still runs with image & sound but no backlight.
Help required :Now I think the LED driver IC maybe at fault but again i have no schematics as there is nothing written on the chip ,no matter what magnification level I use, its blank.(Image 3-InkedSamsung PSU3 attached)
I have checked the MOSFET for LED circuit ,that is not shorted but When after switching off the TV ,I put Multimeter red probe to "Drain" and "black probe" to "Gate" terminals the LED strips light up for a short time. That proves its working.
Additionally I have also checked that it's not the main board at fault ,but PSW itself(Check method -Switch on TV with everything plugged in ,then disconnect the main board cable, if led lights up the issue with main board , if not PSU fault ).
Fault code :Now after switching on tv, Standby LED blinks 3 times,Sound okay ,image okay
Any help next steps will be highly appreciated.
Let me know if you need specific voltage checks at connectors , I can capture an send.
Thank you in advance
Attached Files
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