Samsung UA32D4003BM 32" LED NO POWER

[s_henya]

Hey guys,

My friend asked for a favor for his girlfriends family,
TV wasn't powering, they took it for reapir,
but the shop gave up..

So he brought it to me, there is a red standby light,
TV responds to the remote but not powering up.

Opend and saw they broke a SMD transistor MDD5N40 on the back side of the PSU
they did a terrible job,

I ordered a set of 10 pcs for 6 $ from Aliexpress

replaced the transistor but still no change,

fuses on PSU are good, everything else looks OK,

I need to know if it's a PSU fault or Mainboard problem..

Added a few pics

Any help/ tips would be very appreciated :-)

[s_henya]

Re: Samsung UA32D4003BM 32" LED NO POWER

Anyone? testing points? common problems with these boards?

[T30M31]

Re: Samsung UA32D4003BM 32" LED NO POWER

Have you checked for voltage on the PSU?

The two 82uF 450V capacitors should have more than 300 volts on them. If not then check the bridge rectifier located in the top right section of the photo. The photo is out of focus but it looks like the bridge is labeled BD8015.

[s_henya]

Re: Samsung UA32D4003BM 32" LED NO POWER

T30M31, thanks for replying, I checked for output signails from the PSU to the Logic board, got 13vdc, 5vdc, 0vdc,

that seems right (i think),

i will check voltages on the main caps tommorow and update,
just for my understanding,
The PSU gets 220vac and after rectification it boosts to 300vdc?

[budm]

Re: Samsung UA32D4003BM 32" LED NO POWER

The PFC Voltage booster will kick in and boost the voltage on the main cap from around 325VDC to 370~400VDC when the power supply board receives the PS_ON signal from the main board.
This power supply board does not have voltage booster circuit. So the voltage on the cap should be around 325VDC (if your line voltage is 230VAC)

[s_henya]

Re: Samsung UA32D4003BM 32" LED NO POWER

OK and after reading your trouble shooting manual again
:-) i need to check the voltages between the 2 legs of the cap?
not using a GND on a screw or anything.

[budm]

Re: Samsung UA32D4003BM 32" LED NO POWER

Yes, measure directly at the two legs of either one of those 450VDC caps, those two caps are connected in parallel. Just be careful not to touch anything.

[s_henya]

Re: Samsung UA32D4003BM 32" LED NO POWER

Tested voltages on both caps got 308VDC, (i guess its good)

whats next?

[s_henya]

Re: Samsung UA32D4003BM 32" LED NO POWER

a schematic would be great, but i couldn't find one for the psu/logic board

[tom66]

Re: Samsung UA32D4003BM 32" LED NO POWER

Any outputs from power supply?

[s_henya]

Re: Samsung UA32D4003BM 32" LED NO POWER

yep, but it a littile hard to test, because the connector has 2 rows, and i cant check the inner row,

can i test voltages only with psu connected?

[tom66]

Re: Samsung UA32D4003BM 32" LED NO POWER

You can check the bottom rows, use a piece of wire to get into the pin hole.

[s_henya]

Re: Samsung UA32D4003BM 32" LED NO POWER

Sorry for the delay, was a little busy,

Connector CNN803 Voltages:

pin1 13.05vdc
pin2 3.37vdc
pin3 13.05vdc
pin4 0vdc
pin5 13.05vdc
pin6 2.14vdc
pin7 13.05vdc
pin8 0vdc
pin9 0vdc
pin10 0vdc
pin11 5.25vdc
pin12 5.25vdc
pin13 5.25vdc
pin14 3.29vdc

I've added refence voltages written on the PCB

any ideas what to test next?
(Again no light, or picture on screen, 7 blinks on touch control panel)

[s_henya]

Re: Samsung UA32D4003BM 32" LED NO POWER

i have seen a couple of posts with similar symptoms, caused by logic board, power supply, bad led strips,

service manual cant be found,

realy lost here :-(

[tom66]

Re: Samsung UA32D4003BM 32" LED NO POWER

Backlight should be ON: BLU_ON/OFF is HIGH. Any high voltage to LED strip?

[s_henya]

Re: Samsung UA32D4003BM 32" LED NO POWER

hi tom, im sorry but i didn't understood your question,
how can i test voltages on the led strip?

max voltage that i can test my multimeter can test is 700v

[tom66]

Re: Samsung UA32D4003BM 32" LED NO POWER

High voltage is relative, it's around 60 to 150V for a 32" panel.
You should check each pin of CNL802 to chassis ground.
I am expecting one or two pins with high voltage, then several return wires for each of the series strings.

[s_henya]

Re: Samsung UA32D4003BM 32" LED NO POWER

there are total 4 wires to the led strips: 3 of them are blue and one black.

i will test and update the results in an hour.

[s_henya]

Re: Samsung UA32D4003BM 32" LED NO POWER

OK,

CNL802:

pin1 147Vdc
pin2 N.C
pin3 N.C
pin4 N.C
pin5 N.C
pin6 N.C
pin7 13Vdc
pin8 N.C
pin9 0vdc
pin10 0vdc

Pin9-10 are jumpered.

Are the strips connected in seiries?
One side is connected to TOP1+ and the other to TOP2-?

[budm]

Re: Samsung UA32D4003BM 32" LED NO POWER

It looks like it only has 1 string of LEDS since it only has two wires going to the panel. Pin 7 must be the return line that is connected to the MOSFET and the low value current sensing resistor.
You can cut the Blue wire to allow you to put DC Amp meter in series with that blue wires to see if the LED string will show any current draws for second when the TV is power up.