Flashing Baclight UN60Fh6003 - PFC off

**jason123** · 10-03-2021, 09:34 AM

Help is appreciated as always. I have Samsung UN60FH6003 with power supply BN44-00669A. When you plug it in, the backlight is flashing at roughly 1 Hz. Heat spots on the board, i thought diodes for sure. But when i measure the filter caps voltage, its 162v -pfc is off. This is the cas with or without the main board connected to power supply. LED Diodes checkout. Backlights checkout. Caps at the LED Driver checkout. Thoughts?

**neilc6** · 10-03-2021, 10:26 AM

Bad LEDs can cause flashing on their own and cause the entire string to flash. I would suspect both the power supply and backlights are damaged since Samsungs dont have shutdown protection.

Just had a weird backlight failure on a UN40H203 with dim backlights. Expecting most LEDs were burnt out but only 3 were. Swapped power supplies since I had a spare and problem was still there confirming bad backlights. It only takes one bad LED to affect the whole array.

**jason123** · 10-03-2021, 10:36 AM

Quote:

Originally Posted by neilc6

Bad LEDs can cause flashing on their own and cause the entire string to flash. I would suspect both the power supply and backlights are damaged since Samsungs dont have shutdown protection.

Just had a weird backlight failure on a UN40H203 with dim backlights. Expecting most LEDs were burnt out but only 3 were. Swapped power supplies since I had a spare and problem was still there confirming bad backlights. It only takes one bad LED to affect the whole array.

With the cable from power to leds connected, i don't get stb 5v or 13v to main board. When i disconnect the led cable from power board, 5 and 12.9 v are steady. I will take the panel apart

**neilc6** · 10-03-2021, 01:12 PM

The backlight driver circuitry is fairly burnt up which is an indicator of bad backlights. You should get standby voltage to the main from the power supply. The power supply turns on with a PS-ON signal from the main. Samsungs have pull up resistors on the both PS-ON and BL-ON signals so disconnecting the main will force the power supply and backlights on.

I have little luck repairing LED driver circuits on Samsungs unless its just a shorted diode and typically replace the whole board. You can test the diodes, FET and sense resistor for shorts.

**jason123** · 10-03-2021, 05:38 PM

I am thinking your original suggestion was accurate. Seemd many of the LEDs are shorted. When i test the leds, they all light up (panel is still closed)

The voltage on the tester is very low. One string is 24v and one is 34v. The tv cant have 7 (@3v) leds on one string or 11 on the other?

**neilc6** · 10-03-2021, 06:14 PM

If you search for the strips on Shopjimmy, it shows 6 rows of 14 LEDs = 84 total so approx 252V for all of them in series. Power supply is marked 297V for the LED driver output.

https://www.shopjimmy.com/bn96-29074...strips-new-12/

These style of strips are very common failures in E, H and J model years.

Quote:

Originally Posted by jason123

LED Diodes checkout. Backlights checkout.

When i test the leds, they all light up (panel is still closed)

They aren't all lighting up. There are many shorted. You can't assume they are all lighting up without observing them.

**jason123** · 10-03-2021, 07:10 PM

You are corrrect... 90% of them are shorted and not lighting up. A new set is on order
Thnk you

10-03-2021, 10:26 AM	#2
neilc6 Badcaps Veteran Join Date: Nov 2015 City & State: BC My Country: Canada I'm a: Knowledge Seeker Posts: 1,362	Re: Flashing Baclight UN60Fh6003 - PFC off Bad LEDs can cause flashing on their own and cause the entire string to flash. I would suspect both the power supply and backlights are damaged since Samsungs dont have shutdown protection. Just had a weird backlight failure on a UN40H203 with dim backlights. Expecting most LEDs were burnt out but only 3 were. Swapped power supplies since I had a spare and problem was still there confirming bad backlights. It only takes one bad LED to affect the whole array. Last edited by neilc6; 10-03-2021 at 10:28 AM..

10-03-2021, 01:12 PM	#4
neilc6 Badcaps Veteran Join Date: Nov 2015 City & State: BC My Country: Canada I'm a: Knowledge Seeker Posts: 1,362	Re: Flashing Baclight UN60Fh6003 - PFC off The backlight driver circuitry is fairly burnt up which is an indicator of bad backlights. You should get standby voltage to the main from the power supply. The power supply turns on with a PS-ON signal from the main. Samsungs have pull up resistors on the both PS-ON and BL-ON signals so disconnecting the main will force the power supply and backlights on. I have little luck repairing LED driver circuits on Samsungs unless its just a shorted diode and typically replace the whole board. You can test the diodes, FET and sense resistor for shorts. Last edited by neilc6; 10-03-2021 at 01:16 PM..

10-03-2021, 05:38 PM	#5
jason123 Badcaps Veteran Join Date: Oct 2015 City & State: Reno, Nevada My Country: USA I'm a: Knowledge Seeker Posts: 719	Re: Flashing Baclight UN60Fh6003 - PFC off I am thinking your original suggestion was accurate. Seemd many of the LEDs are shorted. When i test the leds, they all light up (panel is still closed) The voltage on the tester is very low. One string is 24v and one is 34v. The tv cant have 7 (@3v) leds on one string or 11 on the other?

10-03-2021, 07:10 PM	#7
jason123 Badcaps Veteran Join Date: Oct 2015 City & State: Reno, Nevada My Country: USA I'm a: Knowledge Seeker Posts: 719	Re: Flashing Baclight UN60Fh6003 - PFC off You are corrrect... 90% of them are shorted and not lighting up. A new set is on order Thnk you

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