Author Topic: Converting TV to Battery Power --- LCD Backlight Sense?  (Read 145 times)

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Offline NotANewbieTopic starter

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Converting TV to Battery Power --- LCD Backlight Sense?
« on: June 15, 2024, 06:04:22 am »
I'm quite stuck on my project to convert a Toshiba 42in TV to battery power.
Hope to get some help from those more knowledgable.   Step 1 was to replace the gas tube backlight with leds.
I got this working, however, the lcd "pixel board" that connects directly to the lcd has a ribbon cable that went to one of the tube driver boards (there was one each side).  Just disconnecting it and the lcd would not turn on.  However, I discovered if I only connected the ground wire to the tube driver board from the AC power supply, it would then turn on.  The "pixel board" connect had these marked pins  Dimm-In, Gnd, NC, Sens-CB, NC, Gnd, Dimm-Out
The NC (assume not connected) were actually connected to GND (assume it means ground..).
When I tested all these pins when it was working, they all seemed to be grounded.  So I connected them all together with one wire and connected it to the gnd pin on the backlight AC power board, and it works.   But if I connect this to any other ground on the AC board it does not work.
The multimeter shows they are all gnds.   So I am baffled.   I just moved ahead and replaced all the DC outputs on the AC board that go to the controller board dc power supply, and of course, it still doesn't work unless this ground is connected to the backlight ac board gnd.

My guess is that somehow the "pixel board" is not turning on the LCD unless it senses the backlight is on.  There is 24v that is generated for the tube drivers, but I don't have this 24v connected to anything and it still works when just the gnd is connected.   I would only add that when the tv is turned the AC board does not turn on the backlight 24v output until a a 3.3v signal is given, then it turns on the 24vdc output.   So while I get continuity from the other gnds to the backlight gnd, is there some possible way it can tell the 24v is not on?

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