Samsung UN40ES6100, Power supply issue

[crabn]

Hi Everyone,

I got a non-working Samsung TV UN40ES6100. It does not have any power including standby light.
There is several with power supply:

1) Fuse nearby AC inlet blown
2) Diode DQ851 shorted
3) One of the MOSFETs (Part No: 13NM60N) cracked

Then I got a replacement working power supply. It was working fine for a few hours. I tried to turn it on next day. It won't turn on any more. There is standby light. Here are some measurements:

1) Voltage at Fuse: 50 V AC
2) Voltage at C9110 and C9111: not stable 191V
3) Diode DQ851 got shorted again
4) Unplug cable from PSU to mainboard: backlight keeps flashing on and off.

My question is what cause the DQ851 being shorted?
Any other comments are welcome.

Thanks.

[budm]

Re: Samsung UN40ES6100, Power supply issue

When making DC Voltage measurement in the primary side you use the negative leg of the main filter cap as the GND ref for the meter, not the chassis.
When making incoming AC you measure between the HOT (LINE) and Neutral.
DQ851 is connected in parallel with resistor RQ951 which is very low Ohm resistor (1 Ohm: Brown, Black, Gold, Gold), you need to lift one leg of the diode and test it again. i doubt that the diode is shorted.

[crabn]

Re: Samsung UN40ES6100, Power supply issue

Thank you Budm. The same result when I pulled the diode out for measurement.
For the other voltage measurements, I'll it tonight using your suggestions

[cliff_hootarski]

Re: Samsung UN40ES6100, Power supply issue

It's diode, not diot.

[crabn]

Re: Samsung UN40ES6100, Power supply issue

It's diode, not diot.

Sorry. My bad language. I corrected them.

[cliff_hootarski]

Re: Samsung UN40ES6100, Power supply issue

No problem, just trying to make it easier for someone trying to help you.

[budm]

Re: Samsung UN40ES6100, Power supply issue

Thank you Budm. The same result when I pulled the diode out for measurement.
For the other voltage measurements, I'll it tonight using your suggestions

So the diode tested off the board shows <1 Ohms in both direction?
The resistor in parallel would have to have Vdrops high enough to turn on that diode.

[crabn]

Re: Samsung UN40ES6100, Power supply issue

So the diode tested off the board shows <1 Ohms in both direction?
The resistor in parallel would have to have Vdrops high enough to turn on that diode.

I did measure the diode off board again showing 320 Ohms. I might make a mistake before. So is this diode still good?

[budm]

Re: Samsung UN40ES6100, Power supply issue

320 Ohms on both directions? If yes, then it is bad.
I will have to trace out the circuits to see what the function of that diode and the 1 Ohm resistor in parallel are being used for. That diode and the resistor are in the backlights LED power supply section.
PS Board: BN44-00502A

[budm]

Re: Samsung UN40ES6100, Power supply issue

OK, I traced out the function of that diode DQ951 & resistor RQ951 parallel connection, they are for the power supply for the LED driver circuit negative return of the bridge rectifier DIODE DM851~854, so instead of having the negative of the power supply connected directly to the cold side circuit ground, it goes to GND through that diode/resistor parallel connection so the Vdrops on that resistor (it is basically monitoring the current draw in the LED power supply section) is being used to feed pin 5 of the LED driver IC9101.
So on the old board what resistance (off the board) do you have for that diode?
What DCV do you have between the two legs of the main filter cap CP814S? It should be around 380~400VDC range and steady. You can run the power supply board by itself to check the Voltages.

[crabn]

Re: Samsung UN40ES6100, Power supply issue

320 Ohms on both directions? If yes, then it is bad.
I will have to trace out the circuits to see what the function of that diode and the 1 Ohm resistor in parallel are being used for. That diode and the resistor are in the backlights LED power supply section.
PS Board: BN44-00502A

It shows 320 ohms on one side only. The other side is over multimeter range or so.

[budm]

Re: Samsung UN40ES6100, Power supply issue

So it is not bad then.
You need to test DCV on the main cap next.

[crabn]

Re: Samsung UN40ES6100, Power supply issue

OK, I traced out the function of that diode DQ951 & resistor RQ951 parallel connection, they are for the power supply for the LED driver circuit negative return of the bridge rectifier DIODE DM851~854, so instead of having the negative of the power supply connected directly to the cold side circuit ground, it goes to GND through that diode/resistor parallel connection so the Vdrops on that resistor (it is basically monitoring the current draw in the LED power supply section) is being used to feed pin 5 of the LED driver IC9101.
So on the old board what resistance (off the board) do you have for that diode?
What DCV do you have between the two legs of the main filter cap CP814S? It should be around 380~400VDC range and steady. You can run the power supply board by itself to check the Voltages.

Hi Budm. I did some more measurements.

- On the old board: resistance of the DQ851 off board is 330 ohms for one side only.

- On the new board with all cables plugged in: Backlight keeps flashing. This PSU makes click sound. It won't fully turn on. Standby light is on
1) DCV at CP814S is jumping between 380 to 400 V.
2) DCV at C9110 and C9111 is jumping between 118V to 183V.

- On the new board with mainboard cable unplugged, backlight cable plugged in: Backlight keeps flashing. This PSU makes click sound. It won't fully turn on
1) DCV at CP814S is jumping between 388 to 396 V.
2) DCV at C9110 and C9111 is jumping between 133V to 155V.

- On the new board with mainboard cable plugged in, backlight cable unplugged: No Backlight. No click sound. It won't fully turn on. Standby light is on
1) DCV at CP814S is stable at 169 V.
2) DCV at C9110 and C9111 is stable at 0.15-0.16V.

- On the new board with all cables unplugged: No Backlight. This PSU makes click sound. It won't fully turn on. No standby light.
1) DCV at CP814S is jumping between 385 to 400 V.
2) DCV at C9110 and C9111 is jumping between 220V to 262V.

[budm]

Re: Samsung UN40ES6100, Power supply issue

- On the new board with all cables unplugged: No Backlight. This PSU makes click sound. It won't fully turn on. No standby light.
1) DCV at CP814S is jumping between 385 to 400 V.
2) DCV at C9110 and C9111 is jumping between 220V to 262V.

You will not have standby lights because the cable between the power and the main board is not connected.
I need to do more indepth board tracing because I do not expect the Voltages to be bouncing like that with such light load due to no main board connected, no LEDs are connected.
I wonder if your A5V, B5V, B13V are stable.

[crabn]

Re: Samsung UN40ES6100, Power supply issue

- On the new board with all cables unplugged: No Backlight. This PSU makes click sound. It won't fully turn on. No standby light.
1) DCV at CP814S is jumping between 385 to 400 V.
2) DCV at C9110 and C9111 is jumping between 220V to 262V.

You will not have standby lights because the cable between the power and the main board is not connected.
I need to do more indepth board tracing because I do not expect the Voltages to be bouncing like that with such light load due to no main board connected, no LEDs are connected.
I wonder if your A5V, B5V, B13V are stable.

Thank you so much for spending time on helping me.
A5V, B5V, and B13V measured at mainboard cable connector are not stable. Voltage changes with click sound. All cable unplugged.
1) A5V, B5V are between 0.001-5.2V
2) B13V are between 0.009-0.29V

What should I do next?

[budm]

Re: Samsung UN40ES6100, Power supply issue

Thank you so much for spending time on helping me.
A5V, B5V, and B13V measured at mainboard cable connector are not stable. Voltage changes with click sound. All cable unplugged.
1) A5V, B5V are between 0.001-5.2V
2) B13V are between 0.009-0.29V

What should I do next?

OK, so even running the power supply board by itself the A5 (standby 5V) is not even stable, so that will be the section we need to work on first.

[CapLeaker]

Re: Samsung UN40ES6100, Power supply issue

Yep, the A5V has to be stable first.
So with each "click" sound you get either 0V or 5.2V on the A5V rail. Did I understand that correctly?
Is there a possibility to see pictures of your PSU not SJ's?

[crabn]

Re: Samsung UN40ES6100, Power supply issue

Yep, the A5V has to be stable first.
So with each "click" sound you get either 0V or 5.2V on the A5V rail. Did I understand that correctly?
Is there a possibility to see pictures of your PSU not SJ's?

There is no physical damage to any caps

[CapLeaker]

Re: Samsung UN40ES6100, Power supply issue

There shouldn't be any clicking sound. With everything disconnected from the PSU, then plug it to the mains and measure the A5V (pin12) it should be stable. Can you verify that?

[crabn]

Re: Samsung UN40ES6100, Power supply issue

There shouldn't be any clicking sound. With everything disconnected from the PSU, then plug it to the mains and measure the A5V (pin12) it should be stable. Can you verify that?

It is stable at 0V if I did not press "Turn on" button on the remote. No click sound yet
It is between 0-3.2V when I pressed "Turn on" button on the remote. There is click sound now