Samsung UN46D7000 Turns on and Off

[w98seeng]

I bought a Samsung UN46D7000LFXZA today. It's about 3 years old and I got it for $40. BUT, it's not working.

The guy said it turns on and off. After looking online to see what the problem might be, I thought I would take
a chance and buy the TV hoping I could fix it.

When the TV is plugged in, it turns on and about 2 seconds later (just as the Samsung Smart TV lights up on the
screen), the TV turns off, then on, and then off. It will do this indefinitely.

This is what I did do far...

I unplugged the little button bar (power, volume, etc) and still the same problem.

I unplugged all the plugs 1 at a time in numerical order (according to the oicture). The only time it stopped turning
on and off was when Iunplugged #3, the ribbon cable going from the P/S to the M/B. (Can it be the M/B causing the
problem?) I unplugged #'s 5 & 6 (going to the screen) and the screen didn't light up, but the power supply still turned
on and off.



When I disconnected the cable from the main board, nothing happened. No clicking, but the P/S didn't turn on either.

I did a visual inspection of the P/S board with a light and magnifying glass and didn't see any problems. (I know Samsung
TV's have a problem with the caps on the P/S board.)

The only thing that isn't normal is a slight discoloration (dark brown from overheating) around the openings in the red circle.
On the plastic behind the screen panel, the part that comes in contact with the back of the P/S board it a little melted. Is it
normal for this to get that hot?



I took off the P/S board and inspected the back, but nothing look out of place. I inspected the M/B, but there really is
nothing to look for on that board.

Any ideas how I can pinpoint the problem to the P/S or the motherboard?

Thanks,
Ian

[tibimakai]

Re: Samsung UN46D7000 Turns on and Off

I while back I have repaired a 46C6300 by replacing the mainboard.
Right now, I have a 40C6300 which is doing the same thing, but it turns on and of in a second or so, so no image on the screen.
I'm almost 100% sure that is the mainboard. The problem is they are hard to find and they are expensive.
I have removed the PS_ON wire from the connector and measured it, while the TV it was on and it was giving that on and off signal, so I have concluded that the mainboard was bad.

[w98seeng]

Re: Samsung UN46D7000 Turns on and Off

The reason I am leaning towards the power board is because when I disconnect the cable from the main board, the clicking stops, but nothing powers up at all.

All the things I have read about a faulty main board says that when you disconnect the power board cable from main board, the clicking stops and the power board works and lights up the screen.

Also, if the main board was bad, would I get Samsung Smart TV on the screen?

But, I would like to be sure, otherwise I am taking a chance replacing the power board.

Ian

[tom66]

Re: Samsung UN46D7000 Turns on and Off

The trick about removing the cable and getting the backlights to fire on is NOT applicable to the D-series LED onwards. Only older Samsungs (R8, A, B, C and D series CCFL.)

[w98seeng]

Re: Samsung UN46D7000 Turns on and Off

The trick about removing the cable and getting the backlights to fire on is NOT applicable to the D-series LED onwards. Only older Samsungs (R8, A, B, C and D series CCFL.)

This is the problem with looking for a fix as there are so many Samsung models out there, it's impossible for me to know which ones are applicable to my TV.

But, this is good to know because I tried it again and the power board does click only once when I unplug the cable going to to main board. So, does this mean it IS the main board that is toast?

Thanks,
Ian

[audiofreak19]

Re: Samsung UN46D7000 Turns on and Off

No the reason the tv isn't working when u unplug the main board is te main supplies the standby voltage and also recieves the signal from the buttons to turn the tv on. I will look for a service manual and take a look at that. I would recomend getting a DMM and measuring the voltages on the power boards connectors to see if your getting standby voltage and all the right values at the connectors.

[tibimakai]

Re: Samsung UN46D7000 Turns on and Off

You could disconnect the mainboard and use some resistor(1-2.5KOhm) from STBY_5V to PS_ON and another from STBY to BL_ON and see if the backlight turns on.

[w98seeng]

Re: Samsung UN46D7000 Turns on and Off

No the reason the tv isn't working when u unplug the main board is te main supplies the standby voltage and also recieves the signal from the buttons to turn the tv on. I will look for a service manual and take a look at that. I would recomend getting a DMM and measuring the voltages on the power boards connectors to see if your getting standby voltage and all the right values at the connectors.

You could disconnect the mainboard and use some resistor(1-2.5KOhm) from STBY_5V to PS_ON and another from STBY to BL_ON and see if the backlight turns on.

Many thanks for responding. I am a bit of a noob when it comes to this stuff, but I am a fast learner. DMM = digital multimeter? Have one.

I'll be in stand-by mode waiting further info.

Thanks you,
Ian

[tibimakai]

Re: Samsung UN46D7000 Turns on and Off

I have explained there what I would do.
Use a 2.5Kohm resistor and solder it to the standby pin on the power supply connector and the other leg to the turn on pin, PS_ON I guess.
Another 2.5Kohm resistor from the same standby pin to the backlight on pin, which I guess it would be something like BL_ON.
Remove the connector between the mainboard and power supply and turn it on(plug it in). The backlight it should turn on, if the power supply/inverter and LEDs are good.
It this is successful, the only thing left is a bad mainboard.
Lets see what others are suggesting also, I'm not an expert myself either, but I have managed to repair probably around 70 TV, with this forum's help and on my own too.

[mmartell]

Re: Samsung UN46D7000 Turns on and Off

The trick about removing the cable and getting the backlights to fire on is NOT applicable to the D-series LED onwards. Only older Samsungs (R8, A, B, C and D series CCFL.)

Tom that's not entirely accurate as the D6000 works in this way and possibly a few of its close siblings. As for the D7000 he more than likely needs jumpers to fire the backlights.

[w98seeng]

Re: Samsung UN46D7000 Turns on and Off

Use a 2.5Kohm resistor and solder it to the standby pin on the power supply connector and the other leg to the turn on pin, PS_ON I guess.
Another 2.5Kohm resistor from the same standby pin to the backlight on pin, which I guess it would be something like BL_ON.

Thanks for the info tibimakai, unfortunately, my power board does not have these pin outs. This is how my board looks.


Like I said before, I am a noob when it comes to board level electronics, but I am a quick study and I follow directions very well.

Thanks,
Ian

[w98seeng]

Re: Samsung UN46D7000 Turns on and Off

Anyone else with any ideas?

Ian

[tibimakai]

Re: Samsung UN46D7000 Turns on and Off

That looks weird, I haven't seen these marking before.
The BLU ON/OFF it's most likely the turn on for the backlight, POWER_ON is the turn on(PS_ON), I'm a bit confused which one would be the standby, the A5V or the B5V?
You could test it while the TV is plugged in, but not turned on, see which one has the 5V.

[w98seeng]

Re: Samsung UN46D7000 Turns on and Off

You could test it while the TV is plugged in, but not turned on, see which one has the 5V.

Can't do this because as soon as the TV is plugged in, it turns on and off by itself. There is no off.

Possibly a short somewhere that turns the TV on when plugged in?

Ian

[tibimakai]

Re: Samsung UN46D7000 Turns on and Off

You have to unplug the mainboard to do this.

[w98seeng]

Re: Samsung UN46D7000 Turns on and Off

You have to unplug the mainboard to do this.

With the main board unplugged, the power board clicks only once. I do not know if the click is turning it on or just a stand-by mode.

There is a Samsung repair center near me, I think I'll bring in the power board and see if they can test it.

Ian

[tibimakai]

Re: Samsung UN46D7000 Turns on and Off

Mainboard unplugged and those two resistors soldered to those points that I have explained. Then see what will happen. Make sure that you insulate does resistors from touching anything metal or PCB.

[w98seeng]

Re: Samsung UN46D7000 Turns on and Off

Mainboard unplugged and those two resistors soldered to those points that I have explained. Then see what will happen. Make sure that you insulate does resistors from touching anything metal or PCB.

I connected the negative lead to the chassis and with the positive I checked each pin on the power connector going to the main board.
These are the voltages I got, all seem good.

1. OD_LEVEL - 5V
3. OD_ON/OFF - 5V
5. GND
7. B13V - 14V
9. B13V - 14V
11. V amp - 14V
13. V amp - 14V
15. GND
17. B5V - 5V
19. B5V - 5V

2. P-DIM4 -
4. P-DIM3 -
6. P-DIM2 -
8. P-DIM1 -
10. B13V - 14V
12. BLU ON/OFF - 5V
14. GND
16. GND
18. A5V - 5V
20. POWER ON/OFF - 3V

Nothing happened when I jumped the pins to get the backlight to light.

Ian

[w98seeng]

Re: Samsung UN46D7000 Turns on and Off

I downloaded a few Samsung Fast Track Troubleshooting Manuals (they had for the UN55D7000 and the UN60D7000 but not for the UN46D7000) to compare different models procedure on how to get the backlight lit.

The 7000series models say to unplug the cable going to the main board, plug in the TV and the screen should light. I am assuming that since my TV is also a 7000 series TV, the procedure is the same. This does not work when I try it.

So, the voltages are OK across the connector going to the main board but there isn't any light coming fr5om the backlight, how does this help in diagnosing the turning on and off of the TV? What is the next step?

Ian

[tibimakai]

Re: Samsung UN46D7000 Turns on and Off

I'm not and expert, maybe somebody else should help here.
The Power ON/OFF is constant 3V or is oscillating?