as the topic , the sound still good but the backlight gone after 3 and more maybe 5 hours ..and the data still ok to ,just the lamps turn off , and when you turn off the tv and turn on the lamp work good ..
i check the power ( i/p ) seem good anyone have the service manual or any help ,thank you .
Hello, Samsung was common problem with power unit, certainly weak capacitors. If You are familiar with base electronic skills, try disassemble TV and inspect capacitors in power module, if caps are punched out then need replace it. Use Low ESR (low impedance) capacitors for using in PSU systems. Backlight problems is first sign weak powering.
One more question: after power off/on cycle, working time is same (next few hours), or significantly shorter?
If time is similiar long as first run, then maybe problem with CCFL tubes - invertor circuit have overvoltage protection, if CCFL are near end of life then voltage raising and shuts down backlight, after power reset things are back to work.
If second run is very short, the problem maybe in overheating something up to protection level.
Next point - inspect soldering pools, cool-soldering have similiar effects, randomly malfunctioning is typical.
On PCB silkscreen is printed table with voltages, use it to examine PSU under load.
Remark: yellow marked diode on photo is clamp element in protection power MOSFET.
You will not be able to localise an intermittent fault like that. The best option is to fit in a low ohm resistor between Vcc, 12V pin and LD (after disconnecting LD from the balancer board) and observing if the fault re-appears.
when the lamp turn off i puch bottom the power and puch it again then its work well , theris no dry solid , thank you for your help .
mr zbyszekskibinski : you want me to cut wir from board and contect with resistor with 12 vcc this is the photo .
Yes, disconect the wire from the LD pin and connect a resistor from 12V Vcc line to this point on PSU board. You should select a right resistor to obtain about 7V there but this value is not critical, I've seen Samsungs with 12V and 10V on this pin. If the backlight doesn't go off anymore this will tell you a CCFL is at fault.
dear zbyszekskibinski : thank you for your helped , the tv still on more then 10 hours , and i saw something , the customer was putting the brightness and the sharpness on the maximum level , then i minimized them to the medium level .