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Toshiba 46L5200U1 - LED backlight driver board    
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kuhurdler



Joined: 28 Dec 2006
Posts: 2862
Location: Overland Park, KS

PostPosted: Mon Oct 17, 2016 12:27 pm    Post subject: Toshiba 46L5200U1 - LED backlight driver board Reply with quote

Toshiba 46L5200U1
I struggled through an issue with the backlights on this model.
My symptoms seemed slightly different than many others.

My TV turned on, worked fine for 2-20 minutes, then the backlight would flicker a few times and then go dark. If I turned off the TV, the sequence would repeat. It was usually a shorter time if the TV was warmed up.

I assumed it was the backlights, based on the various forums I had found. I took the entire panel apart and none of my LEDs had failed. All were equally bright, and measured the same voltage drop across each lamp.

For troubleshooting purposes, I discovered how to bypass/disable the LED sensing circuits. I'm not responsible for any damage if you follow this technique, and certainly don't leave it this way.



I soldered a jumper connecting the pads of all 4 of these transistors, shorting them together. This basically eliminates the LED protection circuit. They'll have no ability to compare the current measurements of the 4 LED circuits... which keeps the backlights ON regardless of their performance.

After doing this, my TV would stay on for hours, confirming that the LED strings were bad (even though they were all lit and looked fine). I'm not going to lie, it was tempting to just leave it this way. I did end up removing this and replacing the LED strands, and it has been fine ever since.


Last edited by kuhurdler on Fri Oct 21, 2016 12:03 pm; edited 2 times in total
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JTS1957



Joined: 21 Jan 2009
Posts: 2340
Location: Far, Far Away

PostPosted: Mon Oct 17, 2016 3:30 pm    Post subject: Reply with quote

ALL three-legged items on the board are "Q's." I'm presuming that not all are 'Transistors.'

Base/Gate (Emitter/Drain)(Collector/Source) of Q101 to the Base/Gate (Emitter/Drain)(Collector/Source) of Q201 to the Base/Gate (Emitter/Drain)(Collector/Source) of Q301 to the Base/Gate (Emitter/Drain)(Collector/Source) of Q401?

OR

Base/Gate to Emitter/Drain to Collector/Source of EACH of the four transistors/FETs?

OR something other.
kuhurdler



Joined: 28 Dec 2006
Posts: 2862
Location: Overland Park, KS

PostPosted: Mon Oct 17, 2016 9:40 pm    Post subject: Reply with quote

I meant the physical base of the chip... the heat sink on the bottom that is soldered to the board. Though I believe it is electrically connected to the center pin of each chip.

more simply, connect a jumper wire to all the tips of the red arrows that i drew on that photo.
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