Samsung UN60FH6200F TV - No backlight - Please help

[TubeJunkie]

Hello, I have a Samsung UN60FH6200F LED TV with no backlight. It has sound. I can do the flashlight test and can see the image. Here are some voltage readings on the connector that powers the panel. Top connector of power board. Looking at pic, from left to right:

Pin 1. 15.0 vdc (it fluctuates a few volts)
Pin 2. 313. Vdc
Pin 3. 313 Vdc
Pin 4. 416 vdc

I’m in USA, AC line voltage is 120v. No bulging caps. No obvious heat damage to boards. Any help will be greatly appreciated. This is for a friends parents. Hate to see this TV wind up in a landfill. Thanks

[budm]

Re: Samsung UN60FH6200F TV - No backlight - Please help

1) What did you use for meter GND?
2) Lift up one end of diode D9151C in the LED driver section and then use Ohm meter to check the resistance of that diode in both directions.
3) So far it looks like you have open circuit in the LED, or connectors, or wiring.

Power supply/LED driver board BN44-00669A.
https://www.shopjimmy.com/samsung-bn...upply-unit.htm

[TubeJunkie]

Re: Samsung UN60FH6200F TV - No backlight - Please help

Hi budm. Thanks for your reply. My original voltage readings were with negative meter probe to metal chassis ground.

I lifted (unsoldered) the cathode (banded) end of diode D9151C. With ohm meter negative probe on the cathode, red probe on anode, I get 1.85 Mohms. 0 reading with meter leads reversed.

Can I test a mosfet with my multi meter? Q9151C ( 3N50NZ) looks to be part of this same circuit

[budm]

Re: Samsung UN60FH6200F TV - No backlight - Please help

Pin 1 (Actual pin number is pin 9). 15.0 vdc (it fluctuates a few volts).
Pin 2. (Actual pin number is pin 6) 313. Vdc, pin 6 is directly connected to pin 4)
Pin 3. (Actual pin number is pin 4) 313 Vdc
Pin 4. (Actual pin number is pin 1) 416 vdc

You have two LED strings connected in series to form one large LED string, String # 1 is connected to pin 1 and pin 4, string #2 is connected to pin 9 and pin 6 (see the pin names as printed on the board).
The Voltage reading of pin 6 and pin 9 indicating problem in LED string # 2.
The LED Voltage with good load is 297V as printed on the board, but since you have open circuit some where so the Voltage went up over 400VDC.

This may be the LED strips for your panel.
https://www.shopjimmy.com/samsung-bn...-12-strips.htm
Parts for your TV:
https://www.shopjimmy.com/catalogsea...ng+UN60FH6200F

[TubeJunkie]

Re: Samsung UN60FH6200F TV - No backlight - Please help

I was suspecting bad LED’s. I’ve never changed those in a panel, do they solder in? Was there a power supply problem that blew the LED strip? I’d hate to do all that work and still have a problem, and further expense.

[nomoresonys]

Re: Samsung UN60FH6200F TV - No backlight - Please help

When replacing the strips have to be very careful not to break/crack the screen, they break pretty easily, seems the bigger the screen the more flimsy the screen.

[mmartell]

Re: Samsung UN60FH6200F TV - No backlight - Please help

I was suspecting bad LED's. I've never changed those in a panel, do they solder in? Was there a power supply problem that blew the LED strip? I'd hate to do all that work and still have a problem, and further expense.

Failed leds are very common. Most manufacturers drive them too hard out of the box it's therefore recommended the end user turn them down right away to a still comfortable brightness level.

Yes they solder into the strip. The entire strip containing the bad led(s) can also be replaced which is essentially plug and play.

You have nothing to lose at this point as the tv is non functional. You can sell the boards or attempt the repair if you're up for it.

You can always still sell the boards should the repair not go as planned.

[TubeJunkie]

Re: Samsung UN60FH6200F TV - No backlight - Please help

I’m going to attempt the repair. If I’m successful at removing the old LED strips, I’ll order the new ones from ShopJimmy. I’ll update my progress as I go. Thanks for all of your input

[TubeJunkie]

Re: Samsung UN60FH6200F TV - No backlight - Please help

Well, I’ve made it down to the LED strips without breaking anything. Guess it’s time to order the new ones!

Update: new LED strips have been ordered!

Question: Is there a way to test each individual strip?

[neilc6]

Re: Samsung UN60FH6200F TV - No backlight - Please help

You can use a multimeter in diode mode and test each individual LED. Easier if there are test points or you will need to scratch each side of the LED until you see copper. Or you can buy a LED tester which will let you test the entire strip.

[TubeJunkie]

Re: Samsung UN60FH6200F TV - No backlight - Please help

Got the new LED strips, and installed them, reassembled everything. Success. I now have backlights! Picture looks good. I've noticed the power supply board is making a slight buzzing sound. Is this normal for this model? It's not a loud buzzing sound, but I noticed it when I powered it on.

[budm]

Re: Samsung UN60FH6200F TV - No backlight - Please help

Did you turn down the backlights (not Brightness) to as low as you can?

[TubeJunkie]

Re: Samsung UN60FH6200F TV - No backlight - Please help

Yes. Max setting is 20. I set it to 9. Thanks to everyone for all your help!

[Snipeye]

Re: Samsung UN60FH6200F TV - No backlight - Please help

Hey! Not trying to hijack, but I've got the same TV and a related issue. 60 of the 84 LEDS were burnt out, so I just bought entire replacement strips and threw those in - no problem. Even at 20, however, they seem too dim. They kind of flicker from dim to bright, randomly, and when I tested the required voltage with my tester, it gave me ~212 (~108 per group of 3). When I measure the voltage on the connector with the TV plugged in and on, it shows ~208V, so I'm worried something is wrong with the power supply board (tested with main board plugged and unplugged).

That seems pretty far off from the 297V I'm supposed to have... the 3 resistors on the back near the connector that are in parallel (R9151-R9153) are illegible and look maybe burnt, but I'm not sure what value they're SUPPOSED to be, since the only reference image I could find didn't have quite enough resolution. Maybe 3900?

Advice appreciated, happy to test other voltages/things. Thanks!

EDIT: 208V from d+ to d-, roughly 220v from d+ to chassis ground

[Dannyx]

Re: Samsung UN60FH6200F TV - No backlight - Please help

I remember having a fairly close, though not identical, scenario with a PSU from a Samsung once. The only difference is that the power rails on mine were also unstable so the whole set would just shut off. When the PSU was connected on its own, the backlight would flicker as you describe too. Sadly I can't remember for the life of me what I did to it, since I DID fix it but can't remember how. I think it was a bad cap on the secondary after all, but again: the symptoms were slightly different so it may not be of help to you...

[Snipeye]

Re: Samsung UN60FH6200F TV - No backlight - Please help

I appreciate any pointer. What did you do to check for a bad cap? Just look for bulging, measure voltage...?

[Dannyx]

Re: Samsung UN60FH6200F TV - No backlight - Please help

These newer "slimmer" PSUs don't usually show bulging caps, but they can go bad nonetheless....it's one of those repairs which I haven't recorded anything about and now it's killing me that I can't remember how I solved it, for it was a pretty intriguing repair.

Sure, the 12v bus was lower than normal, around 8v and the backlights were flickering like I said, but I did not have anything at my disposal for testing, other than my meter, so nothing fancy really. Now that I think about, it could've been a bad TL431....just a thought, I'm not sure. Can't remember whether or not I posted about it either since I often use BC as a form or diary, but couldn't find anything of the sorts The TL431 was for another Samsung TV which had gone bad, but it was before this one, so perhaps using my previous knowledge, I didn't make too much of a fuss over it and just forgot about it entirely....

EDIT: THIS thread of mine has a PSU which looks familiar to what I recall with the flickering backlight and whatnot, though it's not exactly how I remember it. Give it a read though, just for fun I'd say

[Dannyx]

Re: Samsung UN60FH6200F TV - No backlight - Please help

I found the original thread I was talking about HERE, unfortunately I only had a very vague idea of what it was about and therefore upon reading it now, I realise it doesn't suit your needs at all, since it's a different supply and issue, but I'm still going to leave it here. Cheers.

[Snipeye]

Re: Samsung UN60FH6200F TV - No backlight - Please help

I do appreciate the help... I'm looking for a schematic for this one now, and I'm just not even sure where to start looking. The power to the LEDs seems low, but I've got no clue what that indicates.

[budm]

Re: Samsung UN60FH6200F TV - No backlight - Please help

Hey! Not trying to hijack, but I've got the same TV and a related issue. 60 of the 84 LEDS were burnt out, so I just bought entire replacement strips and threw those in - no problem. Even at 20, however, they seem too dim. They kind of flicker from dim to bright, randomly, and when I tested the required voltage with my tester, it gave me ~212 (~108 per group of 3). When I measure the voltage on the connector with the TV plugged in and on, it shows ~208V, so I'm worried something is wrong with the power supply board (tested with main board plugged and unplugged).

That seems pretty far off from the 297V I'm supposed to have... the 3 resistors on the back near the connector that are in parallel (R9151-R9153) are illegible and look maybe burnt, but I'm not sure what value they're SUPPOSED to be, since the only reference image I could find didn't have quite enough resolution. Maybe 3900?

Advice appreciated, happy to test other voltages/things. Thanks!

EDIT: 208V from d+ to d-, roughly 220v from d+ to chassis ground

If you read my post #4, what do you get on pin 1 without LED connector in place?