Samsung UN50EH5000F won't power on (BN44-00499A PSU)

[staze]

All,

Have one of these units that shutoff sometime over the weekend, and now won't power on for more than a second. Red light is on, power button gets it to make it's happy power on music, then it shuts back off (standby). Red light doesn't flash. Panel never comes up. Same symptom with LED backlight unplugged.

PSU looks okay (physically), and I get a nice 5.38V on A5V, but other than that, not a whole lot. Don't have a scope handy, but will try to get one to look at by the end of the week.

Any other thoughts to look at on this unit?

[budm]

Re: Samsung UN50EH5000F won't power on (BN44-00499A PSU)

At the power supply-LED driver board: Put black probe of the DCV Meter on the chassis GND, then leave the red probe on pin 1 of the LED connector CNL802 and then turn on the TV to see how high the dcv will jump up to (put meter in 500VDC range) and wait 5 seconds to see if it will go back down.
Then do the same aging but this time leave the probe on pin 9 and then Turn the TV on.
Report the readings that you observe.

[staze]

Re: Samsung UN50EH5000F won't power on (BN44-00499A PSU)

Pin 9 never came up above ground. Pin 1 came up to about 0.02V. There are two test points next to CNL802 that say it should read 1.408R? It reads about 2R (1.9R, etc).

Seems like the backlight rail is never firing up...

[dick_barton]

Re: Samsung UN50EH5000F won't power on (BN44-00499A PSU)

Disconnect the power supply from the main board and jumper a 1K resistor from A5V to PS_On/Off then check your voltages. B13V, PWM_DIM, Vamp, B5V, etc.

[staze]

Re: Samsung UN50EH5000F won't power on (BN44-00499A PSU)

Disconnect the power supply from the main board and jumper a 1K resistor from A5V to PS_On/Off then check your voltages. B13V, PWM_DIM, Vamp,B5V

Cool, will do that once I have a 1K resistor handy. =) TV is in the office, all my tools and parts are at home. =P

[budm]

Re: Samsung UN50EH5000F won't power on (BN44-00499A PSU)

The board already has pull up resistors so when you remove the cable between the main and the power board the backlights should come on when the TV is plugged into the outlet.
You can tell if the board has pull-up resistors or not by measuring between GND and the PS-ON pin, it should be 2VDC or more, it will be <1V if it does not have pull-up resistor, same for the BL-ON pin, this is done without having the main board connected..
The LEDs are connected in one long string so if one goes open circuit, you will not see any backlights.

[dick_barton]

Re: Samsung UN50EH5000F won't power on (BN44-00499A PSU)

Here's a trouble shouting guide.


https://cdn.badcaps-static.com/pdfs/...3db525660a.pdf

[staze]

Re: Samsung UN50EH5000F won't power on (BN44-00499A PSU)

okay, backlights powered up immediately when I unplugged the main board, and then plugged unit into mains.

B13V: 12.84V
PWM_DIM: 3.464V
Vamp: 12.84V
B5V: 5.38V
BLU_ON/OFF: 3.003V

[budm]

Re: Samsung UN50EH5000F won't power on (BN44-00499A PSU)

That means the main board is not sending the command signals to the power supply board.
Check the PS-ON (or PWR_ON) and the BLU-ON pin to see what you get when you have all the boards connected to see what is/are missing.

[staze]

Re: Samsung UN50EH5000F won't power on (BN44-00499A PSU)

PWR_ON goes to 3.45V when switched on. BLU_ON remains low. But the TV powers back off before the 5 sec delay that the guide seems to indicate (only stays on for like a second).

Going to check the other rails while the main board is plugged in. Maybe a transistor is blown, so while it hits the voltage, there's no actual current capability? Or am I crazy?

[budm]

Re: Samsung UN50EH5000F won't power on (BN44-00499A PSU)

No BLU_ON = no backlights.
PWR_ON is good, but does it go back down after 5 seconds?
If it does the try disconnecting the cable to the T-CON board ad see what happen.

[staze]

Re: Samsung UN50EH5000F won't power on (BN44-00499A PSU)

All the rails are pretty much the same when "loaded" but remain "on" after the unit shuts back off (red light), for about 15 seconds, then shut down completely.

[budm]

Re: Samsung UN50EH5000F won't power on (BN44-00499A PSU)

the key point is that, does the the PWR_ON signal stay at 3.45V when you said the TV shutdown by itself after 15 seconds.
BTW, it may have gone into STBY if it does not detect video signal after period of times.
BTW, my SAMSUNG TV RED POWER LED is off when TV is ON, when TV is OFF the RED LED stays ON.

[staze]

Re: Samsung UN50EH5000F won't power on (BN44-00499A PSU)

yes, PWR_ON stays "high" for 15 seconds, then drops low. Also noticed the optical out stays lit that whole time.

the screen never lights... I wouldn't think that would be the case if it's in standby. And it shuts itself off after 15 seconds.

[budm]

Re: Samsung UN50EH5000F won't power on (BN44-00499A PSU)

OK, try disconnecting the T-CON board from the main board and see if you can even get the backligths to come on, at this point it looks like you have main board problem some where..

[staze]

Re: Samsung UN50EH5000F won't power on (BN44-00499A PSU)

okay, just plugged another computer into TV. Computer sees the TV as a display, but nothing on the display. Now kind of wondering...

[staze]

Re: Samsung UN50EH5000F won't power on (BN44-00499A PSU)

Unplugged t-con. No change in behavior (backlight doesn't fire).

[staze]

Re: Samsung UN50EH5000F won't power on (BN44-00499A PSU)

BTW, my SAMSUNG TV RED POWER LED is off when TV is ON, when TV is OFF the RED LED stays ON.

Yes, that's exactly what I'm seeing... only, it is KINDA on even when the red light is on. The optical out stays lit for a good 15 seconds. So it's in some type of "standby" before it fully powers off.

[staze]

Re: Samsung UN50EH5000F won't power on (BN44-00499A PSU)

So, mainboard? Guess I could break out the thermal camera... but most of it looks like it'd be worse to replace than just buy a used mainboard online and be done with it. They're SOO cheap.

[budm]

Re: Samsung UN50EH5000F won't power on (BN44-00499A PSU)

Yes, main board problem some where.