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Old 08-23-2018, 01:47 AM
cademan cademan is offline
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Toshiba flat screen tv

Hi all, I usually hang out at AudioKarma. I know electronics and I am mostly into tube equipment and the audio side of things. Anyway, I have a Toshiba flat screen which seems to have an intermittent problem.

I thought I would run it by a few people here who are more knowledgeable with the flat screen technology.

The tv was given to me for free, and it was said that it didn't work but when I got it home and plugged it in, it worked fine..........for about a month but then it went out and now it won't work again. It seems like the back lit panel isn't working right as when you first turn it on, it will flash a picture on the screen but then go dark. The front panel power indicator light used to glow solid green but now only glows for a second and then goes dim.

Would this be a bad capacitor? Bad back light transformer? Power supply? I can easily check these things but just wanted some general input here before I open it up and dive in. My forte' is audio so I am not much of a tv guy or couch potato.

This thing only has one single circuit board with all the parts, and a few wires running to the back light panels. That's it.

Any general ideas?

Appreciate any replies. Thank you!
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  #2  
Old 08-23-2018, 11:16 AM
Electronic M's Avatar
Electronic M Electronic M is online now
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I've only done a couple flat panel displays, but the ones suffering from bad caps would do similar.
If any cans look bulged or like they let gunk out those are definitely bad...Sometimes you need an ESR tester to check. The little $15 Chinese ESR testers on ebay can do this.
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  #3  
Old 08-23-2018, 08:07 PM
cademan cademan is offline
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Great place to start. Thanks!
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Old 08-25-2018, 12:48 PM
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MadMan MadMan is offline
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I would bet on a backlight problem. They're tiny little fluorescent tubes, and like regular fluorescent lights, they get old and stop working. What I've seen happen (in my admittedly limited experience) is that the tubes go bad or weak, and the power supply (think ballast) still sending the tubes high voltage, through tiny wires, and the HV leaks out and arcs to ground. The backlight goes out, obviously, and depending, the power supply may stay on and run the tv anyway, or turn itself off as a sort of failsafe mode.
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Old 09-02-2018, 06:07 PM
cademan cademan is offline
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Hmm, I have some capacitors on order but how would I check the back light?

The people that gave it to me said it quit working but when I actually got it home and checked it out, it worked perfectly for about a month. Not a single glitch or hiccup. Nice and bright with no flicker or dimming.

Turned it off one night and then back on the next day and it started doing again what I presume it was doing before I got ahold of it so possibly an intermittent (hopefully easy) problem.

It has a very simple single power supply board with only two outputs. One for the back light and one for the video board. All diodes, bridge and voltage regulator test good.

Oh well, the capacitors only cost me $10.00.
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Old 09-26-2018, 09:11 PM
mbates14 mbates14 is offline
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if the backlight pulses and shuts down, you should check the inverter board. They have multiple safetys built in, and if it senses that 1 or more tubes dont fire, it will shut down.

Same thing if the board itself cant supply the correct tube current for one reason or another.
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