Samsung un55js7000 no power

[budm]

Re: Samsung un55js7000 no power

Here's a better picture of the bottom of the led connector. The big caps near it had 390ish voltage.

Are you talking about these 4 black caps 22uF 400VDC?
https://www.badcaps.net/forum/attach...5&d=1597966857

If that is the case, you should not be seeing <1V at the LED connector, but then I do not know where you put the probe leads at.

The exposed pin of the LED connector you see on the top side of the board are the odd number pin, pin1 is marked with whit triangle.

Pin 1 is 2+ which is the Anode of LED STRING #2.
Pin 5 is 2- which is the Cathode of LED STRING #2.

Pin 9 is 1+ which is the Anode of LED STRING #1.
Pin 13 is 1- which is the Cathode of LED STRING #1.

Bottom line, if those Voltages on the those 4 LED power supplies filter caps show 390VDC, that means you have open circuit in the LED strings some where due to bad LED's (more than likely), connectors that link the LED strip together, etc.

BTW, you can see the LED Voltage chart printed on the board close byt he connector that goes to the main board. The two LED strings are not the same, one has more LED's than the other.

[Foofles]

Re: Samsung un55js7000 no power

Are you talking about these 4 black caps 22uF 400VDC?
https://www.badcaps.net/forum/attach...5&d=1597966857

If that is the case, you should not be seeing <1V at the LED connector, but then I do not know where you put the probe leads at.

Yeah, those are the caps I'm talking about.
I get voltage at them, but not on the connector to the leds. Measured the resistance on each led strip, and both are infinite resistance.

Checked the voltage with the leds disconnected - still < 1v. My leads were connected from pin 1 to 5.

[budm]

Re: Samsung un55js7000 no power

Lets do the test like this to check the Voltages at the LED connector, LED connector and all other connectors must be in place.

1) TV off, keep black probe on the chassis at all time.

2) Red probe on pin 1 (2+), then turn on the TV while watching the meter to see how high the Voltage jumps up to, record that then wait a few minutes the turn off the TV.

3) Red probe on pin 5 (2-), then turn on the TV while watching the meter to see how high the Voltage jumps up to, record that then wait a few minutes the turn off the TV.

4) Red probe on pin 9 (1+), then turn on the TV while watching the meter to see how high the Voltage jumps up to, record that then wait a few minutes the turn off the TV.

5) Red probe on pin 13 (1-), then turn on the TV while watching the meter to see how high the Voltage jumps up to, record that then wait a few minutes the turn off the TV.

[Foofles]

Re: Samsung un55js7000 no power

Well, I have voltages measuring like that. So, am I a dumbass that was checking the voltage the wrong way?

2+ 313v
2- 235v
1+ 319v
1- 219v
All positive voltages. Shouldn't I be reading two of them as negative?

[budm]

Re: Samsung un55js7000 no power

Well, I have voltages measuring like that. So, am I a dumbass that was checking the voltage the wrong way?

2+ 313v (Anode)
2- 235v (Cathode return to ground via PWM controlled MOSFET Q9253 and current sensing resistors R9265 // R9267).

1+ 319v (Anode)
1- 219v (Cathode return to ground via PWM controlled MOSFET Q9153 and current sensing resistors R9165 // R9166).
All positive voltages. Shouldn't I be reading two of them as negative?

Something is off here, you report 390Vdc readings on those four 22uf 400VDC caps by the LED connector.
Did you measure the Voltages of those caps by putting the probe on each legs of the cap?

Right now the Cathode Voltage reading are way too high.

Remove the LED connector and then retest the 4 pins of the LED connector again.

[Foofles]

Re: Samsung un55js7000 no power

I measured the caps with probes on each of the legs of the cap. I'll check with the led connector disconnected momentarily.

[budm]

Re: Samsung un55js7000 no power

I measured the caps with probes on each of the legs of the cap. I'll check with the led connector disconnected momentarily.

If that is the case I expect to see the same Voltage on the 1+ and 2+, so something is not adding up.

[Foofles]

Re: Samsung un55js7000 no power

1 and 2 - were very low with it disconnected
1+ 315 max
2+ 315 max
1- 1v
2- 1.7v

No, I'm not seeing 390v on the caps. They're all around 300-315. Sorry, I must have made a typo.

[budm]

Re: Samsung un55js7000 no power

1 and 2 - were very low with it disconnected
1+ 315 max
2+ 315 max
1- 1v
2- 1.7v

No, I'm not seeing 390v on the caps. They're all around 300-315. Sorry, I must have made a typo.

OK, that makes sense.
Now I need to find out why the 1- and 2- are reading so high when the LED connector is in place.

BTW, you never see the backlights even flash on for seconds when you first turn on the TV in the dark room, correct?

[Foofles]

Re: Samsung un55js7000 no power

Nope, no backlight at all. Just tested in a dark room.

[Foofles]

Re: Samsung un55js7000 no power

Update...
I borrowed a much nicer meter from a friend and tested the voltage again with everything connected. The positive pin is less than 1v
I do not know why my other meter was reading differently. Hell, maybe I read millivolts as volts.

Definitely getting myself a better meter ... Apologies for wasting time with bad info.

This doesn't really make sense though. I'm going to test a few more times. I'm sure that I read high voltage yesterday.

[budm]

Re: Samsung un55js7000 no power

Update...
I borrowed a much nicer meter from a friend and tested the voltage again with everything connected. The positive pin is less than 1v
I do not know why my other meter was reading differently. Hell, maybe I read millivolts as volts.

Definitely getting myself a better meter ... Apologies for wasting time with bad info.

This doesn't really make sense though. I'm going to test a few more times. I'm sure that I read high voltage yesterday.

Show us the new meter and the setting..

[Foofles]

Re: Samsung un55js7000 no power

Show us the new meter and the setting..

Checked again.......... And now the voltages are high on all pins. I changed nothing. Here's a picture of me checking 2-

Edit - ignore the stray probe on the right. That's a different meter.

[budm]

Re: Samsung un55js7000 no power

Since now your new meter is showing difference reading, you need to repeat the test in step #23 with and without LED connector in place.
BTW, You must put all the board mounting screws back in place, I see that you put the black probe on the board with no board mounting screw on it.
The boards are grounded to the chassis with board mounting screws.

[Foofles]

Re: Samsung un55js7000 no power

Since now your new meter is showing difference reading, you need to repeat the test in step #23 with and without LED connector in place.
BTW, You must put all the board mounting screws back in place, I see that you put the black probe on the board with no board mounting screw on it.
The boards are grounded to the chassis with board mounting screws.

Sorry, I was unclear - when I tested it again, the new meter is getting high voltages on all pins just like my old meter was.
I think maybe a probe was loose when I saw the < 1v while LEDs were connected.

So - it's as it was before.

Connected-
1+ 2+ 320v max
1- 225v max
2- 245v max
Disconnected-
Same except both - pins were < 1v.

I'm playing with it now, and it doesn't seem to turn off when I press the power button ...
Edit - it may not be turning off because the power button is also the select button. Who knows what menu I'm in.
Double edit - universal remote allows me to turn it off.
Triple edit - was finally able to display something on it. I can see the image when I hold a flashlight to the screen.

[Foofles]

Re: Samsung un55js7000 no power

Is there anything I can do to test the led strips?

[budm]

Re: Samsung un55js7000 no power

Is there anything I can do to test the led strips?

I would suggest getting the LED tester, opening the LCD panel is the last thing you want to do since you can easily damage the screen.

https://www.ebay.com/sch/i.html?_fro...Desc=0&_sop=15

[Foofles]

Re: Samsung un55js7000 no power

I would suggest getting the LED tester, opening the LCD panel is the last thing you want to do since you can easily damage the screen.

https://www.ebay.com/sch/i.html?_fro...Desc=0&_sop=15

Yeah, I'm not really excited about the thought of possibly getting to the LEDs.

Do you think bad LEDs could cause what I'm seeing with the voltages? I'm not sure what else to check on the psu board.

[budm]

Re: Samsung un55js7000 no power

Right now you are seeing the 320V due to the LED power supply is not seeing the loads, so it can be dues to open circuits in the current paths of the LED to ground returns through the constant current control circuits..
Failed LEDs are common failure, but fail LED driver can also be the problem.
There is LED Voltage and current rating chart printed on the board.
Do you stock any resistors?

[Foofles]

Re: Samsung un55js7000 no power

Right now you are seeing the 320V due to the LED power supply is not seeing the loads, so it can be dues to open circuits in the current paths of the LED to ground returns through the constant current control circuits..
Failed LEDs are common failure, but fail LED driver can also be the problem.
There is LED Voltage and current rating chart printed on the board.
Do you stock any resistors?

Yeah, I have plenty of resistors of various ratings laying around