Samsung UN55H6203 - Power Supply BN44-00774A

[jason123]

Hi folks,

I got this TV dead - backlight was out. Almost 50 LEDs out of 70 were charred - I don't know how it worked till it got to this point.

Anyway, replaced all bad LEDs, assembled the unit, and it worked beautifully. I navigated menus, lowered Backlight setting and went to grab a bite.. when I came back the TV had turned off, and a burn smell in the room.

Now, no STB (13 V is now 1.6 V), the large cap has 164 V on it (PFC is not on)

I'm assuming the standby circuit went out, or whatever generates the 13V? LEDs are not on with the Main board disconnected as you'd normally expect.

Any help is appreciated. I ordered a new power board - just was curious how bad this board is damaged.

Thank you

[R_J]

Re: Samsung UN55H6203 - Power Supply BN44-00774A

Have you unpluged the led's to see if you get 13v back? check all the secondary diodes including d9101 for shorts, check Q9101c

[jason123]

Re: Samsung UN55H6203 - Power Supply BN44-00774A

Yes... 1.6 with everything unplugged.. plugging things back, this 1.6 drops to 1.5 V - no backlight

I saw this video https://www.youtube.com/watch?v=JgrZ0X8LCzw
Seem to imply it's a known issue?

[R_J]

Re: Samsung UN55H6203 - Power Supply BN44-00774A

If Q9101 is shorted, you should be able to remove it and you should get the 13v back (but the backlights won't operate with Q9101 removed)

[jason123]

Re: Samsung UN55H6203 - Power Supply BN44-00774A

I remove it off the board... not quite shorted.. 82 ohms across pins. What's odd is without it the TV fired up with backlights and full function. I powered it off right away though.

[R_J]

Re: Samsung UN55H6203 - Power Supply BN44-00774A

That mosfet is for the led boost voltage, so the backlights were operating just from the raw voltage so they will likely light but be dim.

[jason123]

Re: Samsung UN55H6203 - Power Supply BN44-00774A

FET on order... thank you

[jason123]

Re: Samsung UN55H6203 - Power Supply BN44-00774A

Got the FET today.. TV was responsive.. bright backlight.. then it turned off Lost my 13 V again, but the FET is not shorted.

[R_J]

Re: Samsung UN55H6203 - Power Supply BN44-00774A

check if any of the diodes, shorted, you can also lift one end of DM841c and DM843C and see if the 13v comes back, if it does, the fault is in the backlight circuit

[jason123]

Re: Samsung UN55H6203 - Power Supply BN44-00774A

DM851, 54, 55 AND 56C are no longer being reported as diodes. The smaller diodes (41 42 43 44c) seem to check out

[R_J]

Re: Samsung UN55H6203 - Power Supply BN44-00774A

DM851, 54, 55 AND 56C are no longer being reported as diodes. The smaller diodes (41 42 43 44c) seem to check out

What do you mean by "no longer reporting as diodes"? what are you checking them with?

[jason123]

Re: Samsung UN55H6203 - Power Supply BN44-00774A

I use smart tweezers...in diode test mode...they usually show direction and Vf.... it does on the smaller diodes. The large diodes are reported as not diodes

[R_J]

Re: Samsung UN55H6203 - Power Supply BN44-00774A

Get a multimeter with diode test and check them, The diodes are likely schottky diodes and that hair plucker does'nt detect them.

[jason123]

Re: Samsung UN55H6203 - Power Supply BN44-00774A

Hair plucker is a birthday gift from the kids.. have to use it..
With my Fluke 87 V, I see all diodes are fine. Schottky (large) are 0.166 V and smaller are 0.465 V Vf.

[R_J]

Re: Samsung UN55H6203 - Power Supply BN44-00774A

Are you getting any voltage on the +13v like before? (1.6v)
Check the voltage across the main primary filter CP810s, is it 160vdc or 385vdc?
Check the voltage between J812(hot ground) and DM808 cathode

[jason123]

Re: Samsung UN55H6203 - Power Supply BN44-00774A

initially after the TV shut off (after replacing the FET), there was no voltage on 13V. After unplugging from the wall and reapplying power, I am getting 12.79 V on the 13V pins

[R_J]

Re: Samsung UN55H6203 - Power Supply BN44-00774A

So the power supply is working?

If it is intermitint, resolder the connections on the transformer, sometimes the rivets around the pins get intermitint.
The other thing I would replace are the three smaller caps in the primary, CM816, CM813 & CP807, the power supply is always on and these caps can dry out overtime and the power supply wont start sometimes.

[jason123]

Re: Samsung UN55H6203 - Power Supply BN44-00774A

Yes / Maybe? No backlight. On the backlight connector I see >290 V (fluctuates between 276 and 309 V) on M1+ (pin 1) and close to 0V on all the other pins on that connector.

[R_J]

Re: Samsung UN55H6203 - Power Supply BN44-00774A

If you are getting 290v on the led connection, you MUST have 13v. So the normal led operating voltage is about 268v The reason you have a higher voltage is due to the led string being open. I suspect another bad led in the string or bad connection during the last repair

[hdguy]

Re: Samsung UN55H6203 - Power Supply BN44-00774A

Did you ever figure out what was up with your TV? I have all the EXACT same symptoms.

I can solder but the waiting game and shipping for parts tends to lead me to replacing full boards. In this case, I can't tell if the Power Supply is bad, or it is just the LED strips. LED Tester will be here in 3 days, but I wonder if I should buy a power supply too.

What is really throwing me off is why am I getting fluctuating volatages of 290v-320v on M1+ when turned on, nothing on M2, M3, M4 or M5. And M1+ is steady at 167v when in standby.