Samsung un49mu7000f dead no power

[lotas]

Measure the resistance (between "+" and "-") on the LED strip relative to the TV ground in kOhm or MOhm.

[howardc64]

Measure the resistance (between "+" and "-") on the LED strip relative to the TV ground in kOhm or MOhm.

Here are the measurements taken on CNL802 (LED backlight connector on PSU)

unplugged : 1+ 1- 2+ 2- to each other and to chassis all OL

plugged results

https://docs.google.com/spreadsheets...it?usp=sharing

• 2+ 1- shorted is also observed on my known good Samsung UN55KU PSU so must be the correct design although I don't understand it.
• Some resistance values continuously increase and decrease. I guess measuring a charging cap?
• Some resisteance value are different if red/black OHM meter probe reversed. I guess maybe polarized cap?

[lotas]

No, you misunderstood me. The power supply is probably working, but the ground voltage protection on the LED strips is triggered. I asked you to disconnect the LED strips from the power supply and measure the resistance on the strips themselves between the "+" and ground and between the "-" and ground. All four wires relative to ground in kOhm, MOhm.

[howardc64]

No, you misunderstood me. The power supply is probably working, but the ground voltage protection on the LED strips is triggered. I asked you to disconnect the LED strips from the power supply and measure the resistance on the strips themselves between the "+" and ground and between the "-" and ground. All four wires relative to ground in kOhm, MOhm.

Yes I did this test. Unplugged the connector and checked 1+ 1- 2+ 2- to chassis. All are OL. Also check 4 connections against each other, all OL

[howardc64]

Yes I did this test. Unplugged the connector and checked 1+ 1- 2+ 2- to chassis. All are OL. Also check 4 connections against each other, all OL

ok I think I proved LED strip is shorting to chassis only when turning on

All boards and connectors plugged in. VOM in diode mode. - probe on chassis, + on either 1+ or 2+ of LED connector. Plug in TV, backlight flicker occurs and periodic beep.

Will order LED strip.

[howardc64]

ok I think I proved LED strip is shorting to chassis only when turning on

All boards and connectors plugged in. VOM in diode mode. - probe on chassis, + on either 1+ or 2+ of LED connector. Plug in TV, backlight flicker occurs and periodic beep.

Will order LED strip.

More definitive test

Disconnect LED connector from PSU (PSU is not involved in the test)
VOM diode mode - probe to chassis, + probe to 2+
LED tester + probe to 2+, tester - probe to 2- light up #2 LED circuit, whenever tester - probe is removed from 2-, there is a brief beep on VOM

So 2+ has a short to chassis whenever #2 LED circuit transitions from lit to not lit.

[howardc64]

Fixed backlight but unfortunately broke the LCD in upper corner while removing the outer frame Only put slight pressure on the LCD to pop free the frame and it cracked. Probably due to rigid metal outer frame (most are plastic) Lesson for future is pop the corners free with pry tool from underneath.

Anyway, backlight had a short that only occurs when turned on. The LED strip is screwed on to the chassis so if any LED has a short from + to LED bar, then its a short to PSU ground.