Samsung UN60J620 Backlight or PS?

[jason123]

Hi Folks,
Troubleshooting a TV that doesn't have backlight (Flashlight tests ok - I am getting data on screen - no backlight)

I see Firmware ICs and PS repair kits on eBay in addition to the obvious bad Backlight.
I'd hate to open up the panel to find a different problem though.
So here are some measurements I was hoping someone can tell if it's backlight or something else.

Main board is getting 13V standby and does generate the 3.3 PWR_ON signal

On the Power supply board:
D+, D- = 417 V
S+, S- = 402 V

(guessing if D+ and D- are same voltage then there is no current flow = translate to open LEDs?)

Readings above are when TV is on, and referenced to COM (Chassis)

I tested the problematic Diode - it has 417 V across it. Upon removal, it has 0.7k ohm, and 3.9 k ohm (keeps going up)

Any other measurements to take to confirm the diagnosis?
When I apply voltage from D+ to S-, and S+ to D- I get some LEDs lighting up. I don't have the panel open, so I don't know how many if any are dead LEDs.

Thank you
Thank you all

[budm]

Re: Samsung UN60J620 Backlight or PS?

Which Diode? What is the designator for that Diode, Dxxxx?
It is bad if it shows resistance in both directions.
Board: BN44-00775A

[jason123]

Re: Samsung UN60J620 Backlight or PS?

D9001C... from other posts you've helped on, the same resistance was the issue. You think it's bad with these readings?
Yes, this is the BN44-00775A

[neilc6]

Re: Samsung UN60J620 Backlight or PS?

If you want to fix TVs, you need to invest in a LED tester. 80% of TVs I repair have bad LEDs and I use my LED tester more than my multimeter. Pay a bit more for one that is higher current.

[jason123]

Re: Samsung UN60J620 Backlight or PS?

I have a home rigged 380 V with adjustable current from 3 to 25 mA. I have used it for years.. bulky and ugly but it does the job.. i think

[budm]

Re: Samsung UN60J620 Backlight or PS?

D9001C... from other posts you've helped on, the same resistance was the issue. You think it's bad with these readings?
Yes, this is the BN44-00775A

" it has 0.7k ohm, and 3.9 k ohm (keeps going up)"
Replace it.
See the LED driver topology, if the diode is leaky you will get same Voltage reading on D+ and D-.
Also check SMD resistors R9032/9033 right by the LED connector.

[neilc6]

Re: Samsung UN60J620 Backlight or PS?

A LED tester will read back the voltage across the probes so you can tell right away if you have an open or lots of shorted LEDs without opening up the panel. I have also used the tester to power up the backlights independent of the power supply to confirm a tv has video and the screen is good before ordering new strips.

To test a diode, unsolder and lift up one leg and put your multimeter in diode test mode. It will read a voltage drop forward biased and open reverse biased. If shorted, it will read 0V both directions.

[jason123]

Re: Samsung UN60J620 Backlight or PS?

A LED tester will read back the voltage across the probes so you can tell right away if you have an open or lots of shorted LEDs without opening up the panel. I have also used the tester to power up the backlights independent of the power supply to confirm a tv has video and the screen is good before ordering new strips.

To test a diode, unsolder and lift up one leg and put your multimeter in diode test mode. It will read a voltage drop forward biased and open reverse biased. If shorted, it will read 0V both directions.

Thank you.. might invest in a tester.. any specific brand or kind?

[jason123]

Re: Samsung UN60J620 Backlight or PS?

Thanks budm... great help as always.. yes Diode is bad. Replaced and backlight is back on.

[neilc6]

Re: Samsung UN60J620 Backlight or PS?

Something like this does 300mA but looks like euro plug. https://ebay.us/2MDAX3 May be cheaper on Aliexpress.

I would play a blank white test video or display a plain white jpeg and look for dark patches to see if you have shorted LEDs.

[budm]

Re: Samsung UN60J620 Backlight or PS?

Thanks budm... great help as always.. yes Diode is bad. Replaced and backlight is back on.

Great, make sure to set the Backlights level on all input to as low as possible to extend the life of the LED's.
Do the white screen test as suggested too.

[jason123]

Re: Samsung UN60J620 Backlight or PS?

Will do.. thank you budm and neilc6

[budm]

Re: Samsung UN60J620 Backlight or PS?

BTW, you can use the LED tester to test Zener diode, and diode (rated >300 Volt) too.

[jason123]

Re: Samsung UN60J620 Backlight or PS?

I'll have to circle back once i get it. Excited to get it now. Thank you

[zape]

Re: Samsung UN60J620 Backlight or PS?

" it has 0.7k ohm, and 3.9 k ohm (keeps going up)"
Replace it.
See the LED driver topology, if the diode is leaky you will get same Voltage reading on D+ and D-.
Also check SMD resistors R9032/9033 right by the LED connector.

Just checking it to say thanks to budm
D9001C was faulty in my case too.
replaced it with some random high voltage diode and the TV is workin!

[zape]

Re: Samsung UN60J620 Backlight or PS?

in my case it was both the D9001 diod and the LEDs, almost half of the leds were dead