Sound and picture but no backlight

[JCdes]

Re: Sound and picture but no backlight

Better picture of my U200 readings...

[budm]

Re: Sound and picture but no backlight

59.8 on stdby 62.4v turned on. It does spike to 72 for a second then back to 62, power off is back to 59.8. Same behavior on all connections.

Are you saying that with the LED connector in place ALL 5 pins of the LED - pins show the same reading as the LED +? That will not make sense at all because you have Boosted Voltage fed to the Anode of the five LED strings so the Cathode return pins cannot have the same readings as the LED + (Anode of the LED string), to have the same readings on Anode and Cathode mean all LED strings are shorted out which at this point I doubt that, more like measurement error.
The 59V is the feeding Voltage to the boost converter.

[JCdes]

Re: Sound and picture but no backlight

Nope I never said the negative pins are energized... I said I get the same reading with and without the led plug connected. If I mentioned something misleading sorry.

[budm]

Re: Sound and picture but no backlight

Can I see the high res straight shots pictures of the whole bottom side of your board and also closeup of the LED connector (bottom side)?

[JCdes]

Re: Sound and picture but no backlight

What Gets my attention is that there's no voltage at the gate pin on the driver.

[JCdes]

Re: Sound and picture but no backlight

Hi res I doubt it... I got my phone camera that's all.

[JCdes]

Re: Sound and picture but no backlight

Check my reply I edited it... No voltage on ground pins

[budm]

Re: Sound and picture but no backlight

Nope I never said the negative pins are energized... I said I get the same reading with and without the led plug connected. If I mentioned something misleading sorry.

I do not understand.
"59.8 on stdby 62.4v turned on. It does spike to 72 for a second then back to 62, power off is back to 59.8. Same behavior on all connections."

What I am trying to understand is what the Voltage reading on the LED connector wires (LED -): Black, Gray, Blue, Black, and White wires are.
So they are 0V then based on your edit.

[budm]

Re: Sound and picture but no backlight

What Gets my attention is that there's no voltage at the gate pin on the driver.

Your meter cannot read high switching frequency, it must be present other wise you will not be seeing the 72V boosted Voltage, and it may be higher than 72V because your meter may be too slow to catch the peak Voltage reading. There will be no Gate drive if you measure it when it goes into protection shutdown.

[budm]

Re: Sound and picture but no backlight

It has 5 led strips consisting of 14 leds each. I dont know the value of each led. The tester starts from 0v increasing the voltage to the strip and it lights up very dim at around 70v and stops increasing at 83v full brightness. Tried disconnecting the "adj" wire on the board and that did not work, just wanted to try and see if it made a diff.

So each one of the five LED string show 83V when tested with LED tester?

[JCdes]

Re: Sound and picture but no backlight

Yes

[JCdes]

Re: Sound and picture but no backlight

All leds light up, I took it apart to do the test.

[JCdes]

Re: Sound and picture but no backlight

Is there any chance it could be the transistor?

[budm]

Re: Sound and picture but no backlight

Right now I am trying to find out how those 5 MOSFETs which the LED Cathode returns of the LED strings are connected to are driven, if those MOSFETs are not turned on then the LED strings will not light up that is why I need good clear pictures of the bottom side of the board. I has to be something that is common to all 5 LED strings that fail to function.
BTW, you never see the LED even light up for seconds when TV is turned on, correct?
What spare resistor do you have in stock? any 100 Ohms or so resistors?

[JCdes]

Re: Sound and picture but no backlight

Does this work?

[JCdes]

Re: Sound and picture but no backlight

I have 100 ohm resistors... No, the leds don't even blink.

[budm]

Re: Sound and picture but no backlight

That is really good, now you need to remove that black rubber bumper so I can see the traces connected to the LED connector.

[JCdes]

Re: Sound and picture but no backlight

Here it is, seem like the ground traces

[budm]

Re: Sound and picture but no backlight

Can you read what is printed on Q201 by the LED connector?

[JCdes]

Re: Sound and picture but no backlight

On the top side?