Samsung UN55F7050AFXZA ver. TD01 power cycling

[high-tech]

Hello everybody, I could use some help on this one... It's got me guessing...
I took pictures of all the boards and the pin out of the connector on the power supply that goes to the main board... I measured all the pins in relation to chassis ground, here are the result.

(B13v)1. 12.7 volts cycling (Vamp) 2. 12.7 volts cycling
(B13v)3. 12.7 volts cycling (PWM5) 4. 1.0 volts cycling
(OD_LE)5. 2.8 volts cycling (PWM4) 6. 0.9 volts cycling
(OD_ON)7. 2.8 volts cycling (PWM3) 8. 0.9 volts cycling
9. ground (PWM2) 10. 0.9 volts cycling
(B13v) 11. 12.7 volts cycling (PWM1) 12. 0.9 volts cycling
(B13v) 13. 12.7 volts cycling (B13v) 14. 12.7 volts cycling
(Vamp) 15. 12.7 volts cycling (BLU_ON) 16. 4.4 volts cycling
(Vamp) 17. 12.7 volts cycling 18. ground
19. ground 20. ground
(B5v) 21. 5.3 volts cycling (A5v) 22. 5.3 volts steady
(B5v) 23. 5.3 volts cycling (PS_ON) 24. 3.3 volts cycling

The only voltage that remains steady is the 5 volt circuit on pin 22 im assuming is the stanby voltage...

I also checked all the led circuits un plugged with an external LED tester and they all lit up, I know this because I took the screen out and visually saw each LED light up. And all of the +L1 through + L5 have voltage on them with +L2 & +L3 being a higher voltage because there are more leds on those circuits...

So basically I think I eliminated the power supply and the leds as being the fault, I can't find anything wrong there. If I unplug the T-con board the power cycling stops but the screen is dark in the middle from top to bottom with the top of the screen lit up and the bottom of the screen lit up. This is an edge lit screen having leds on both sides. So circuits 2 and 3 on both strips aren't lighting up I don't know why but it is what it is.

Any Help would be appreciated Thank you...

[budm]

Re: Samsung UN55F7050AFXZA ver. TD01 power cycling

Please put the pin name for all those pins so we can easily what each pin is for.

[high-tech]

Re: Samsung UN55F7050AFXZA ver. TD01 power cycling

I did as you requested.

[Kilroy2k1]

Re: Samsung UN55F7050AFXZA ver. TD01 power cycling

If you plug the T con back in and unplug the ribbons going to the screen, one at a time with the opposite one back in,can you stop the power cycling?

[high-tech]

Re: Samsung UN55F7050AFXZA ver. TD01 power cycling

it still does it with both screen cables unplugged.

[Kilroy2k1]

Re: Samsung UN55F7050AFXZA ver. TD01 power cycling

Check all caps for shorts on the t con and if there are any transistors or fets check those too.

[high-tech]

Re: Samsung UN55F7050AFXZA ver. TD01 power cycling

Well I checked the t-con board for shorts and didn't find any... I also powered up and checked the voltage at the main fuse on the t-con board and it goes up to 12.48 volts in between power cycles...

[Kilroy2k1]

Re: Samsung UN55F7050AFXZA ver. TD01 power cycling

If you remove the cable thats between the mainboard and power supply, will all the backlights come on and stay on?

[high-tech]

Re: Samsung UN55F7050AFXZA ver. TD01 power cycling

no the middle two circuits L2 & L3 and R2 & R3 wont light up but when I remove the screen and put my led tester on those 4 circuits they light up with an external LED tester...

[high-tech]

Re: Samsung UN55F7050AFXZA ver. TD01 power cycling

I have voltage on +L2 + L3 +R2 +R3 but when I put my volt meter to any of the 2s and 3s plus and minus I dont get the voltage... If I go from chassis with my negative probe and put my positive probe on the +2s and +3s I get voltage... all the rest of the led circuits I can probe the plus and minus and get voltage without going to chassis ground with my negative probe. I think the LED driver controller chip vibrates the negative side of the circuit to regulate voltage and current and I dont think the 2s and 3s are getting oscillation... I dont have a scope to test with all i have is a volt meter...
I sent this power supply off to a repair service and the idiot sent it back and said it was ok there was nothing wrong with it.

[Kilroy2k1]

Re: Samsung UN55F7050AFXZA ver. TD01 power cycling

When you had the screen off and you lit up the led's did any of them seem to slightly flicker at all?
I had one where 1 single led flickered like the old CCFL's did when they started going bad. It caused enough of a problem where the power supply would shut off on protect.