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5 Sharp LC-50LB481U replaced bad LED's, still no backlight!- RESOLVED
Okay I’m back with ANOTHER broken Sharp Roku TV. Model # LC-50LB481U. It had all the signs of a bad backlight- fully functional and you could see the picture with a flashlight. I took the entire TV apart, found the bad LEDs and replaced the strips. After putting it all back together there is still no back light. It seems as if the correct voltage is not being supplied. I can light the LEDs by using my LED tester at the respective harness connector.
I have tested the voltage at the LED harness connector and about 16 volts are being supplied where the LED tester would otherwise supply 59 to bring the LEDs on.
I pulled voltages at the connector from the main board to the power supply (pics below):
Top Row : 6.1V (fluctuating), 3.4V, GND, GND, 12.1V, 12.1V , 12.1V, 0
Bottom Row: 6.7V (fluctuating), 0V (no continuity), GND, GND, 12.1V, 12.1V , 12.1V, 0
As always, thanks for the help!
Back of Power board: A little blurry, I will take again and repost.
Update (07/26/2020)
Better picture of back of power board :
Update (07/31/2020)
Okay after replacement of the power supply board my TV is now operating normally. I am surprised that the TV required both LED strip AND Power Board replacement but it is what it is I suppose.
Bu iyi bir soru mu?
1,4b 
@jostewcrew Need your expert eye again!
Christopher Hill tarafından
@chillin014 .... heya, from what you have posted... looks to be the power supply board. unplug the connector from the main board and check the power supply side to see if your 5v returns. compare your readings to the original.
pro tip: always start with the power supply board. check voltages against print screen legends for voltages, if off, unplug peripheral boards and check again. if still off, troubleshoot power supply, if returns to normal, plug in one board at a time and check for irregularities to start to hone in on issue.
jostewcrew tarafından
@chillin014 ...lets see the back side of the power supply board.... ill scan the front side in the mean while
jostewcrew tarafından
@jostewcrew You rock!. I will post momentarily!
@jayeff you also rock! That makes sense. So I unplugged the main board connector (with the tv powered on, otherwise it would not power on). The 15 and 16 volt terminals remained the same. They actually read, and have always read, a fraction of a volt (.07 V).
When unplugging the main board connector the back lights flickered on very briefly. I replicated this to make sure I saw correctly. I don't know if this has any significance.
I hope to eventually be able to diagnose down to the component. Would be nice to spend $1.00 fixing a board rather than $30-40 replacing it. The power board components look simpler/easier to solder, the main boards not so much.
Christopher Hill tarafından
@chillin014 ... np mate. youll get to be able to do component work soon with the rate youre going. with the right investment in tools, smd work isnt a problem. its all in the troubleshooting. easier with schematic. knowledge will come....quicker than you expect.
while youre posting the pic , afterwards... hook up the power supply one last time. dont connect anything. at the connector to the backlights (unplugged) test the terminals immediately as the unit powers on (power button) record the max voltage reading ( use min max setting on meter) do this for each led + ( you have 3, gonna do it three times) red on +, black on chassis for ground. post your findings while i look over the pic of the back.
jostewcrew tarafından
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