Samsung - LE46C750R2K - BN44-00341A PSU - No Power

[ocf]

Hello Guys and Gals,

I have a 46" that wont turn on, standby light flashes four times slowly then one time fast then repeats. No clicking or noises from back of TV.

All caps look good and voltages look good. When Mainboard is disconnected from PSU and power button is pressed the backlight comes on. Another forum post suggested this shows it is a mainboard issue.

I found a burnt 5w resistor on psu and a few of the mosfet leads around this resistor look dry, I have resoldered the connections but not replaced the resistor.

The resistor is marked 5WR05K what Ohm value is this? 5w 5k ohm resistor?

Do you guys have any past experience with this model of TV or PSU?

[sordids999]

Re: Samsung - LE46C750R2K - BN44-00341A PSU - No Power

Posting pictures of the back of your tv showing the boards with clear pictures may help you more with fixing your problem

[vinceroger69]

Re: Samsung - LE46C750R2K - BN44-00341A PSU - No Power

a shopjimmy picture is here showing the resistor in question RP821
http://assets.shopjimmy.com/media/ca...341a-top_1.jpg
I have had a quick look but cant find any information regarding it im sure budm maybe able to advise on what can be fitted there.

[ocf]

Re: Samsung - LE46C750R2K - BN44-00341A PSU - No Power

Spot on Vince, it is RP821 but that shopjimmy link doesn't work for me. I can only find board schematics for the B Revision of the PSU and RP821 on the B revision is a completely different resistor.

Images below, let me know if you need any more detailed pics I have a DSLR at home

[budm]

Re: Samsung - LE46C750R2K - BN44-00341A PSU - No Power

0.05 Ohm 5W 10% TOL.
That section is the PFC Voltage booster circuit, the resistor is connected to the Source pin of the PFC MOSFET.
Does it show open circuit?

Pictures provided by shopjimmy.
Your pictures are too blur for me.
You have to report the DCV readings on the connector of the power supply board that goes to the main board first, make sure to put the pin names and pin numbers follow by the DCV reading so we can see what are missing.

[ocf]

Re: Samsung - LE46C750R2K - BN44-00341A PSU - No Power

Here are voltages on cable from PSU to mainboard, CN802

All the B13V lines seem stable untill I measured them for more than a 5 seconds, every 7 seconds they drop to 0 then go back to 12.28.

What could be causing this?

Pin Number - Pin Label - Voltage Measured

Pin 1 - B13v - 12.28
Pin 2 - 5vDet - 0
Pin 3 - B13v - 12.28
Pin 4 - BluOn - 0.06 (could be 0v)
Pin 5 - B13v - 12.28
Pin 6 - EPWM - 0.7
Pin 7 - Ground
Pin 8 - Hsync - 5
Pin 9 - Ground
Pin 10 - Ground
Pin 11 - B5v - 5
Pin 12 - Ground
Pin 13 - B5v - 5.19
Pin 14 - B5v - 5.19
Pin 15 - B13v - 12.28
Pin 16 - A5v - 5.19
Pin 17 - B13v - 12.28
Pin 18 - PSON - 0.72

[ocf]

Re: Samsung - LE46C750R2K - BN44-00341A PSU - No Power

How can I measure a 0.05ohm resistor surely my meter will just see no resistance that low.

[dick_barton]

Re: Samsung - LE46C750R2K - BN44-00341A PSU - No Power

How can I measure a 0.05ohm resistor surely my meter will just see no resistance that low.

No, It will see a virtual short circuit (0.00) which is OK. Resistors tend to go high in value or open circuit (OL) when faulty

[budm]

Re: Samsung - LE46C750R2K - BN44-00341A PSU - No Power

Here are voltages on cable from PSU to mainboard, CN802

All the B13V lines seem stable untill I measured them for more than a 5 seconds, every 7 seconds they drop to 0 then go back to 12.28.

What could be causing this?

Pin Number - Pin Label - Voltage Measured

Pin 1 - B13v - 12.28
Pin 2 - 5vDet - 0
Pin 3 - B13v - 12.28
Pin 4 - BluOn - 0.06 (could be 0v)
Pin 5 - B13v - 12.28
Pin 6 - EPWM - 0.7
Pin 7 - Ground
Pin 8 - Hsync - 5
Pin 9 - Ground
Pin 10 - Ground
Pin 11 - B5v - 5
Pin 12 - Ground
Pin 13 - B5v - 5.19
Pin 14 - B5v - 5.19
Pin 15 - B13v - 12.28
Pin 16 - A5v - 5.19
Pin 17 - B13v - 12.28
Pin 18 - PSON - 0.72

That must be an error reading on the PSON pin, if it is at 0.72V then the rest of the switched power supplies (B5V, B13V) will not be on.
Monitor the PSON pin to see if it is going up and down between >2.5VDC and 0.72VDC.

[ocf]

Re: Samsung - LE46C750R2K - BN44-00341A PSU - No Power

PSON Pin shows 0.7v which drops to 0v every 5-7 seconds then returns back to 0.7v.

Along with this drop to 0v there is a very very feint clicking sound coming from the direction of the mainboard.

If I unplug the mainboard the PSON pin stays at 0.78v and doesn't drop at all, backlight also turns on when I unplug the mainboard. Click also seems to stop.

[budm]

Re: Samsung - LE46C750R2K - BN44-00341A PSU - No Power

<1VDC should not be enough to turn on the reset of the power supply, so something is not making sense as far as the signal lvel of the PSON is concerned.
Since the backlights come on, it is telling me that the power supply, the backlights circuits, and the backlights are OK, it is the PSON signal that is going up and down that causes the DC output Voltages to be going up and down because the power supply is being turned on and off.
At this point you have main board problem.

[budm]

Re: Samsung - LE46C750R2K - BN44-00341A PSU - No Power

OK, I look at the diagram of the BN44-00341B, the PSON of 0.7V = ON is correct, we are basically see the Vbe of the PSON switched transistor.

[ocf]

Re: Samsung - LE46C750R2K - BN44-00341A PSU - No Power

Thanks for the replies budm,

Are we still talking a mainboard issue if the 0.7v pson is good. Anything I can check on the mainboard side?

[budm]

Re: Samsung - LE46C750R2K - BN44-00341A PSU - No Power

You can try heating and cooling the main board to see what will happen.

[ocf]

Re: Samsung - LE46C750R2K - BN44-00341A PSU - No Power

I gave the board a heat/cool cycle with a heatgun, got it to about 100C, no change, tv wouldnt boot when board was hot or when it had cooled down.

Should I cover plastic components then bake it in an oven with a Thermocouple to keep an eye on temps?

Was the heating/cooling cycle about confirming whether the board is faulty and reacts to hear or a reflow?

[jczarniak]

Re: Samsung - LE46C750R2K - BN44-00341A PSU - No Power

Hi,
Did you managed to fix the TV, please?
Was it power supply?
I've got very similar problem with my TV.
Thank you.

[CroTech]

Re: Samsung - LE46C750R2K - BN44-00341A PSU - No Power

Hi,

OCF did you manage to diagnose what was wrong with the board, I got the same TV and experiencing same symptoms.

Thanks

[dick_barton]

Re: Samsung - LE46C750R2K - BN44-00341A PSU - No Power

What voltages do you have on PSU connector CN802 as in post #6

[CroTech]

Re: Samsung - LE46C750R2K - BN44-00341A PSU - No Power

Sorry. I can not currently measure it, cause I only have the power PCB with me. I will write the measurings as soon as I can.

[Jimmy1979]

Re: Samsung - LE46C750R2K - BN44-00341A PSU - No Power

Hello
Does someone have the service manual of this PSU bn44-00341a
Thnx