Jvc led tv

[redriddick]

Hi guys,

A friend has given me a jvc led tv to fix. The tv powers up fine but there is no backlight. I have done the flashlight test and the picture is there. Of course the psu is a vestel unit but I don't think that is the problem as I have a pay that does work. Same problem with both Paul's that is leading me to think it's an led strip.
Any ideas guys?

[budm]

Re: Jvc led tv

1) TV OFF, all connectors in place. Keep the read meter probe on the pin of the red wire (Anode of the LED string) of the LED connector, Black probe on the chassis then turn on the TV to see how high the Voltage jumps up to then wait 10 seconds to see how low it goes down to.
2) Repeat the same test on the Black wire of the LED connector.
3) Report the results.

[redriddick]

Re: Jvc led tv

Cheers budm, will try that and report back

[Wilderone]

Re: Jvc led tv

Do the test as Budm suggests but yeah these are prone to backlight failure.
Have done 3 in the last few months.

[redriddick]

Re: Jvc led tv

Morning,
Red point is 80 and drops to 36
Black point is 37 and drops to 0

[budm]

Re: Jvc led tv

Morning,
Red point is 80 and drops to 36
Black point is 37 and drops to 0

So the boost converter is working, but the Cathode return (connected to the LED driver IC) is showing quite high Voltage of 37V, I expect it to be 10V range or so, the high reading may be due to shorted LEDs but if that is the case then you should see the backlights flash on for seconds that it will go into over current shutdown mode, or the return line is not completed circuit to GND via the LED driver IC. This is where the LED strip tester come in handy.
Here is the schematic (Note: your board version may not have all the parts installed as shown in the schematic).
The LED driver IC is MP3394.
Check to see if the PWM signal from main board to the power supply board connector is present or not.
What is the LCD panel model number?
Can we see the hwole top and bottom side of the power supply board and the whole back side of the TV showing all the boards?

[redriddick]

Re: Jvc led tv

Hi,

Pics attached of back of tv, psu and lcd panel number.

[redriddick]

Re: Jvc led tv

What is led tester?

[budm]

Re: Jvc led tv

What is led tester?

examples: https://www.ebay.com/sch/i.html?_fro...ester&_sacat=0

[redriddick]

Re: Jvc led tv

How can I find out what voltage I need to test the leds.?
I previously tested some on a different tv using 9v batteries in series

[redriddick]

Re: Jvc led tv

How can I find out what voltage I need to test the leds.?
I previously tested some on a different tv using 9v batteries in series

[budm]

Re: Jvc led tv

Well, you need to know how may LEDs are connected in series and know if they are 3V or 6V LED (you use constant current source and Volt meter to find out what the Vf (Forward Voltage) of the LED is). LED is the current device so you must limit the current being forced through the LED.
You should use variable power supply with adjustable current limiting.
So did you get to the LED strips yet?

[redriddick]

Re: Jvc led tv

Not at the leds yet?

[redriddick]

Re: Jvc led tv

Is the next step to get to the Lee's?