Samsung UE40F6270 won't come out of standby

[SvenH]

Does anyone have a schematic of the power supply board of a Samsung UE40F6270 TV, type L46ZF_DSM / BN44_00616A ?

See photo attached.

Symptom: after 3 weeks of being powered off, our 4 year old Samsung UE40F6270 died 1 day after using it again. That is: when on standby, it does not turn on; there is the relay clicking on, then off (few seconds, random interval), and the red standby light flashing.

Voltage measurements on connector to main board (left bottom corner on photo) when switching on: 5V = 5.2V; 13V = 7.5V. So I suspect there's something up with the latter.

I am happy to replace capacitors but the closer I can get to the prime suspect, the better.

[Hamie]

Re: Samsung UE40F6270 won't come out of standby

If you disconnect the mainboard and apply power does the backlight come on? If so recheck voltages.

[SvenH]

Re: Samsung UE40F6270 won't come out of standby

Yes the backlight comes on, however it seems to flicker a bit. And there is a mild whining noise coming from near the center of the power board that seems to be in sync with the flicker.

In this state, the voltages measured on the connector to the main board are the same: 5V = 5.2V and 13V = 7.5V.

[budm]

Re: Samsung UE40F6270 won't come out of standby

I would re-solder all the transformer legs, especially those with through hole rivets, and also the legs of those devices mounted on the heatsink.

[Davi.p]

Re: Samsung UE40F6270 won't come out of standby

If you watch the secondary side of the main transformer, the biggest that passes the big white line, you see diodes and double diodes, ho much voltages you have on cathode of them? You will find 7,5v and another voltage for the backlight, then detach the backlight plug and retest.

[SvenH]

Re: Samsung UE40F6270 won't come out of standby

Before soldering I have done a few more measurements as suggested.

Please find attached a picture with numbers of voltage measurements taken just now.

mainboard cable unplugged, backlight plugged in

transformer
1 = 7.5 - 7.8 V
3 = 7.5 - 7.8 V
rest 0 V

diodes - anode
7 = 8.0 - 8.2
8 = 7.5 - 9.0
9 = 7.8 - 9.2
10 = 7.7 - 8.0
cathode
11 = 0 V
12 = 20-24 V
13 = 0 V
14 = 20-24 V

both cables unplugged

transformer
1 = 18 - 24 V
3 = 18 - 24 V
rest 0 V

diodes - anode
7 = 18-21
8 = 18-23
9 = 18-23
10 = 18-23
cathode
11 = 0 V
12 = 68-69 V
13 = 0 V
14 = 68-69 V

[Davi.p]

Re: Samsung UE40F6270 won't come out of standby

The measurements on the transformer and on the anodes usually does not reaveal anything useful, i've noticed a little error in the picture, a middle diode have 13-9 swapped, also is very strange those 2 values on the cathodes at 0v, i think you swapped values, anyway it seems that the tension for the lamps is about 24v with lamps in and 70 with lamps out so i suspect some bad leds on the screen (is an hard job fixing it) or bad step up converter for leds, bye.
Note: the cathode on a diode is the leg with band marked side.

[SvenH]

Re: Samsung UE40F6270 won't come out of standby

Hi Davi.p, you're right, 12-8 and 13-9 I have anode/cathode wrong. If it's some bad LED or bad step up converter, why am I not getting 13V toward the main board even with LED cable disconnected? I am ready to pay $50 to get a new PSU board delivered at this point.

[Davi.p]

Re: Samsung UE40F6270 won't come out of standby

In your measurements i guess those 2 0v was 7,5v , this is because 13v and 70v exit from the same transformer/psu stage and it becomes overcharged by a short, so the tensions falls, the 5v come out from another stage and is good, but buying a new psu is risky because most of the backlight problems are caused by bad leds, one can investigate further , example opening the screen (risky) and test all the bars with a separate supply or one by one with 2 stylus batteries..

[SvenH]

Re: Samsung UE40F6270 won't come out of standby

Update. I have resoldered transformer + components on heatsinks, no effect.
As as test I parallel installed a 13V power supply near the 13V exit toward the mainboard. The TV now comes on, power light blinks at normal pace (without extra 13V it is blinking in panic mode it seems), after about 15 seconds CLICK the TV shuts off again.

I am hesitant to open up the screen to test the LED bars. Any other suggestions besides getting a new PSU board? Thanks all.

[Davi.p]

Re: Samsung UE40F6270 won't come out of standby

Now i see better without tablet... why don't you photograph the tables on the board near the uper left white connector as in the pitcure?

[SvenH]

Re: Samsung UE40F6270 won't come out of standby

Here a detailed photos of the table near the backlight connector and near the mainboard connector.

[Davi.p]

Re: Samsung UE40F6270 won't come out of standby

You can detach the lamps connector, feed power to the power board detached from mainboard and see the voltages on the pins Power-onoff and BLU-onoff, if them are at higher than 1,5v then you have to put them to GND with a wire, if them are lower take a small 3v battery and connect it to the pins at lower voltages, then feed power to power board, see if at least in the first seconds you have all the voltages, so the 13v and the 100-more volts to the lamps connector, if yes you have a good power board. You can force the backlight output to stay on always if there is a protection circuit but i need schematic..

[Hagis2k]

Re: Samsung UE40F6270 won't come out of standby

Well i think you have to disassemble the tv further...

As i do with the sets from samsung is place 2 shoeboxes on a table let them be a bit smaller then the screen, then place towels over them to protect the panel.

Now try to carefully release all clips and let the bezel fall down on the table below, after that take some masking tape and secure all corners on the panel to the plastic frame.

Now remove the speakers, cover for the panels circuitboard, release the connector with the flatflex and then carefully pull it out of the holder and let it hang freely in the air but be careful with it if you bust it your tv is scrap!

Then next take your fingers and release the plastic hooks, start in the corners it is time consuming and having 4 bolts with some cord attached helps so you can lift the metal backplate, and you can also use like a normal knife not a sharp one but a regular one you use when you eat with that you can carefully lever the backplate up and now you shall stick some plastic card between in each corner.

And after you got all 4 sides lose you need to lift the top and bottom side up and look for some tape that fixes the plasticfilms/diffuser to the backplate need to remove it, after the back panel is free grab the cord and carefully lift the entire backlight assembly/backplate up watch out that it does not snag on anything.

Then cover the panel/frame/diffuser/filter assy with a soft cloth to avoid so much dust on it.

I can guarantee you have some failed led strips.

Change the bad one out and either lower the backlight settings or as i did modify the powersupply to lower the voltage out i changed two resistors from 0.27 to 0.56 dropped the voltage on first channel from 180V to 164V and second channel 136V to 127V, this takes the leds from 3.46V down to 3.15-3.25 way less heat now.

And i assume they are built about the same way...

[budm]

Re: Samsung UE40F6270 won't come out of standby

Can I get good clear high resolution straight shot of the bottom side of the power supply board? I need to trace out the circuits.
BTW, you have two set of LED strings thus two Boost converter circuits and two LED controller circuits.

[SvenH]

Re: Samsung UE40F6270 won't come out of standby

Hi all, it has been a while but I finally found the time to pop in a replacement PSU board from eBay. And the TV works again... mostly: now I have (on all sources: TV, HDMI, YouTube...) some dimmed (not off, dimmed) backlight in a horizontal row at the top of the screen (about the top quarter). This happens at all backlight settings (0-20, I typically have it at 10-12).

Does anyone have a clue what that might be?

[Dannyx]

Re: Samsung UE40F6270 won't come out of standby

Yes: dead LED somewhere, no doubt about it. You need to open up the panel and repair/replace the busted string.

As for the PSU: I had a similar issue in the past which drove me nuts: low voltage on the 13v output and flickering backlight. I ended up replacing the PSU since the chap was in a hurry, but I managed to fix the original one as well. I THINK it was a bad capacitor on the secondary after all, despite not showing any signs of immediate failure. I'll see if I can find that post.