TOSHIBA 65l945VQ Backlight problem

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Toshiba Television

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Moshe @moshiko

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Publicada: 11 de set de 2020

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TOSHIBA 65l945VQ Backlight problem

Trying to fix a Semi-Working TV I got for free.

There is a picture, but the backlight is ON only in one-quarter of the screen:

*The screen after disassembly

For a brief period when turning on the TV, all LEDs flicker fast for about 1s period.

then just one quarter remains lit.

I couldn’t find anything obviously wrong with the LED control board

no bulging CAPS or something obviously burned.

power supply lines to that board from the main PSU (8 lines of 24V) all seem to work.

I’ve unplugged and plugged all relevant connectors

Any advice on what can be wrong…

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oldturkey03 @oldturkey03

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Publicada: 11 de set de 2020

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@moshiko check the individual LEDs. I am sure you’ll find one or two that have failed and may cause the array to behave like it does. If you can get your hands on a LED backlight tester you could get this reasonably quick diagnosed. Just in case you do not it will most likely be the LED driver board and there are no schematics readily available. So, a replacement may be needed.

Remember that Toshiba is just another company like APPLE and many others, who enforce planned obsolescence by not releasing any service manuals or any service information to people like us. So we cannot expect any assistance from them in that aspect.

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@oldturkey03 Thank you for the advice!

I was hoping to see some obvious burned out less, but couldn't find any.

Unfortunately, I don't have a dedicated LED tester, but I do have a lab PSU, so I will try to test them with that.

Yes, I know a modern electronic device with a published mfg' service manual is a very rare exception these days and planned obsolescence is the cause.

on a deeper level, it's an inherent evil in our modern excessive consumerism driven market, with all it's accompanying negative effects on the environment, resource depletion etc.

so I view fixing 'old' (anything which isn't the latest) stuff, beyond the immediate benefit as fundamentally positive affect. (lol sorry for the tirade)

12 de set de 2020 por Moshe

@moshiko yes, that will work. You are absolutely right about the inherent evil of our behaviors and we need to stop feeding the Profit-Before- People (Planet) machinery. Let's fix things instead of replacing them!

12 de set de 2020 por oldturkey03

Hey, you were right!

It was a single burnt-out led.

the entire array was flashing briefly, so I took a video, and in a few frames you could see, one area (6 leds) which was not flashing. I found the faulty one.

fixed it first by replacing with a zerner diode (9v), but it was overheating when the display was bright. then resoldered it with a random smt led from an old led lamp.

then the array turned on and worked well.

unfortunately, after assembling the entire thing, the backlight was working well, but the picture goes haywire after the initial intro screen (which surprisingly shows a full screen 'TOSHIBA' well). seems like some rendering chip is ovrheating or is quite screwed.

Anyway, I learned a lot trying to fix this.

13 de set de 2020 por Moshe

@moshiko great job fixing the backlight. The rest sounds like either a main or t-con board issue. Keep on picking away. You got that!

13 de set de 2020 por oldturkey03

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@oldturkey03 Thank you for the advice!

I was hoping to see some obvious burned out less, but couldn't find any.

Unfortunately, I don't have a dedicated LED tester, but I do have a lab PSU, so I will try to test them with that.

Yes, I know a modern electronic device with a published mfg' service manual is a very rare exception these days and planned obsolescence is the cause.

on a deeper level, it's an inherent evil in our modern excessive consumerism driven market, with all it's accompanying negative effects on the environment, resource depletion etc.

so I view fixing 'old' (anything which isn't the latest) stuff, beyond the immediate benefit as fundamentally positive affect. (lol sorry for the tirade) — Moshe
@moshiko yes, that will work. You are absolutely right about the inherent evil of our behaviors and we need to stop feeding the Profit-Before- People (Planet) machinery. Let's fix things instead of replacing them! — oldturkey03
Hey, you were right!

It was a single burnt-out led.

the entire array was flashing briefly, so I took a video, and in a few frames you could see, one area (6 leds) which was not flashing. I found the faulty one.

fixed it first by replacing with a zerner diode (9v), but it was overheating when the display was bright. then resoldered it with a random smt led from an old led lamp.

then the array turned on and worked well.

unfortunately, after assembling the entire thing, the backlight was working well, but the picture goes haywire after the initial intro screen (which surprisingly shows a full screen 'TOSHIBA' well). seems like some rendering chip is ovrheating or is quite screwed.

Anyway, I learned a lot trying to fix this. — Moshe
@moshiko great job fixing the backlight. The rest sounds like either a main or t-con board issue. Keep on picking away. You got that! — oldturkey03

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TOSHIBA 65l945VQ Backlight problem

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