Samsung No Backlight

[jderimig]

Model LN32D450, Sound, no pic, picture evident with flashlight.

History. Watching TV, went to bathroom, returned with no backlight.

Turned off and on, picture returned for 5 minutes then black.

Since then on power on, no backlight, no flicker on power on nothing but audio.

Tried new inverter board off Ebay. no change.
Measured DC voltages on inverter board. VCC =12v LD (whatever that is) 12V. 5V AC going to transformer module thingy inputs.

Any suggestions on next steps for troubleshooting/measuring?

--john

[budm]

Re: Samsung No Backlight

How about the pictures of the whole back side of the TV that shows how all the boards are connected?

[jderimig]

Re: Samsung No Backlight

Pic: Inverter board intentionally pulled out from CCFL connections.

[budm]

Re: Samsung No Backlight

What is the P/N of that power supply-inverter tranformer driver board? BNXX-XXXXX?

[jderimig]

Re: Samsung No Backlight

Bn44-004388

[jderimig]

Re: Samsung No Backlight

Correction: bn44 00438B

[budm]

Re: Samsung No Backlight

OK, I found good clear pictures of the power supply/inverter driver board atshopjimmy but it does not have the pictures of the bottom side of the board, I will the pictures to trace out the connections of the Inverter transformers driver circuit.
Do you also get any DCV at the connector CN802 BLU_ON (backlights on) pin when TV is on?
You also need to check the DCV between the two legs of the main filter cap CP803 to see if it has >360VDC when TV is turned on.

[jderimig]

Re: Samsung No Backlight

OK, I found good clear pictures of the power supply/inverter driver board atshopjimmy but it does not have the pictures of the bottom side of the board, I will the pictures to trace out the connections of the Inverter transformers driver circuit.
Do you also get any DCV at the connector CN802 BLU_ON (backlights on) pin when TV is on?
You also need to check the DCV between the two legs of the main filter cap CP803 to see if it has >360VDC when TV is turned on.

No 360V on filter cap. 160VDC off, ~156VDC on.

Pic of PCB bottom

[budm]

Re: Samsung No Backlight

No 360V on filter cap. 160VDC off, ~156VDC on.

Pic of PCB bottom

OK, you need to find out then why you are not getting the PFC Boosted Voltage, you need to get that working first, the inverter circuit needs that boosted Voltage to work.
Check the Diode DP802, DP810, verify that you do have P-ON (PS-ON) signal on pin 2 of CN802.

[jderimig]

Re: Samsung No Backlight

OK, you need to find out then why you are not getting the PFC Boosted Voltage, you need to get that working first.
Check the Diode DP802, DP810, verify that you do have P-ON (PS-ON) signal on pin 2 of CN802.

Thanks Budm,

Question. Since I have audio does that mean that the PS-ON signal is there?

[budm]

Re: Samsung No Backlight

Yes, more likely but verify it any way.

[ReeceyBurger123]

Re: Samsung No Backlight

Them mainboard the flaming epprom always seem to corrupt I have repaired 3 of them. Unhook the main power connector going from the psu to the mainboard and see if the backlight comes on ?

[jderimig]

Re: Samsung No Backlight

Them mainboard the flaming epprom always seem to corrupt I have repaired 3 of them. Unhook the main power connector going from the psu to the mainboard and see if the backlight comes on ?

There is only one connector going from psu to mainboard. Do I disconnect AFTER i power up? Otherwise the psu doesn't power up.

[budm]

Re: Samsung No Backlight

You disconnect the cable first then plug the TV into the outlet, if the power supply board has pull-up resistor for the PS-ON and the BL-ON control lines then the backlights should come on and you should also have >360VDC on the main cap, but since we do not have the diagram for the power supply board so we do not know if the board has pull-up resistors or not. That is why we need to verify if we do have PS-ON, if you do then you should have >360VDC on the cap, if not then you need to fix the PFC section which will be inspecting those two diodes I mention earlier. There are step by step in narrowing down the problem.

[jderimig]

Re: Samsung No Backlight

You disconnect the cable first then plug the TV into the outlet, if the power supply board has pull-up resistor for the PS-ON and the BL-ON control lines then the backlights should come on and you should also have >360VDC on the main cap, but since we do not have the diagram for the power supply board so we do not know if the board has pull-up resistors or not. That is why we need to verify if we do have PS-ON, if you do then you should have >360VDC on the cap, if not then you need to fix the PFC section which will be inspecting those two diodes I mention earlier. There are step by step in narrowing down the problem.

Can I measure those diodes in circuit or do I have to remove them to check?

[budm]

Re: Samsung No Backlight

You can test them in circuit for now, if the readings do not look right then you will remove them and test them off the board.
BTW, the picture of the bottom side has large glare which makes it hard for me to see the traces.

[ReeceyBurger123]

Re: Samsung No Backlight

So does the psu bring up the pfc and do the backlights come on with the mainboard unplugged ?

[jderimig]

Re: Samsung No Backlight

Diodes check out good (~0.4Vf). Backlight not on when mainboard is not connected.

Just need to figure out how to get the probe on PS_ON pin. Its on the RA connector with the pin in the back row. I will post a better photo in a few.

[jderimig]

Re: Samsung No Backlight

Here's a better pic of back psu

[budm]

Re: Samsung No Backlight

Do those diode has MURXXX on the body? 0.4Vf seems low to me. Set meter to OHM mode and check the resistance both ways with the meter.