Samsung LN40E550

[budm]

Re: Samsung LN40E550

Please enlighten me on this...why would the outside connections (2) still read ~.1 ohms with the Dual rectifier removed from the circuit? I wish I had a correct schematic...this would be so much easier......there are some components on the schematic & on the board that I have, in which I am not familiar.

You can see that the two outside legs copper pads are directly connected together.

[budm]

Re: Samsung LN40E550

what is this suppose to represent??.....A transformer? ....Just trying to get a better understanding on some of the unfamilair items on this schematic. Sorry if I'm being a PITA! Please bear with me as it has been a few years since I was expised to these 'new fangled' items on a scematic.

TM801S is a transformer with many windings.

[stonoguy]

Re: Samsung LN40E550

Would it be OK to plug the set to the AC, apply 120 V and see if the 5.3 vdc standby is present?.....

[budm]

Re: Samsung LN40E550

Yes. You can run the power supply board by itself without having any other board connected to it, the STBY is an always ON power supply.

[stonoguy]

Re: Samsung LN40E550

OK..before I power up, I did some checking and found that the 2 rectifiers that were highlighted in previous pix, have an ohms reading of .3 (reference...cold ground) on the 2 outside connectors.....you said, those 2 are connected to each other. Are these 2 rectifiers going to a transformer that connects to ground after the windings? Do you have any idea where I can get a correct schematic for this board? It's very frustrating not knowing if measurements are correct.

[stonoguy]

Re: Samsung LN40E550

I powered up that PS board and measured 5.2 DCV.......the part I ordered has not arrived yet. The part(s) ID on the schematic I have, do not match the numbers on the components on the board. Confusing.......this is the first time I have run into this. This has been a learning experience....for sure! I have never run into 3 leg rectifiers nor rectifiers mounted on a heat sync. New stuff for me. Thanks for putting up with my ranting. The part that I ordered was not found @ Mouser or DigiKey. I finally found one on Amazon. "I'll be back."

[stonoguy]

Re: Samsung LN40E550

BTW.....That 5.2 dcv was the stand-by voltage.......

[budm]

Re: Samsung LN40E550

BTW.....That 5.2 dcv was the stand-by voltage.......

So you do have the STBY 5.2V with the main board connected or not connected to the power supply board?

[stonoguy]

Re: Samsung LN40E550

No other boards are connected to the power supply board. I still haven't received the replacement part, so I was hesitant to connect the main board.

[stonoguy]

https://www.badcaps.net/forum/images/editor/attach.gifRe: Samsung LN40E550

I connected the main board to the power supply board and got these results:

POWER SUPPLY PCB
Plug CN 802
Pin 13 (B5V) 0 V
Pin 12 (A5V/stand-by) 5.2 V

Plug on Main PCB going to IR:

3.3 V going to IR from (I assume)
Pin 3 3.3v

[budm]

Re: Samsung LN40E550

So the 5.2VSTBY is fine when the main board is connected to the power supply board, but you do not have the switched B5V which is turned on when the power supply board gets the PS-ON signal from the main board.
You need to locate and check the PS-ON pin on the connector of the power supply board to see if it is present or not.

[stonoguy]

Re: Samsung LN40E550

Please explain about PS-ON.......is this a dc voltage?

[stonoguy]

Re: Samsung LN40E550

I have found the PS-ON connection on the CN802...Pin 14.
3.48 v.

[budm]

Re: Samsung LN40E550

Oh, I forgot that you had found shorted MOSFET that you are waiting for the replacement. So right now the STBY power supply is working and you do have PS-ON.
You might as well check the DCV between the two legs of the main filter cap in the primary side to see if you do have the 400VDC booted Voltage between the two legs of the main filter cap or not. Be careful since you are working in the deadly primary side of the circuit.

[stonoguy]

Re: Samsung LN40E550

Nope.....~164.8 Vdc (Hot ground)......the set is not operating, so this would be the voltage in the stand-by mode?

[budm]

Re: Samsung LN40E550

It must be partially working otherwise you will not have the PS-ON Voltage which is generated by the main board when power switch is activated, when the power supply receives that PS-ON signal it will turn on the PFC Voltage booster circuit and other switched power supply sections.

[stonoguy]

Re: Samsung LN40E550

OK....just waiting on replacement part. Hopefully, I will receive it SOON! I am anxious!
Does the 13v/5.3v feed the audio/video circuits? The original problem was the set would go ON/OFF every 30-35 seconds or so. I didn't get to inspect very much, as the set was dead after turning it off and trying to turn it back ON.......I can't swear to it, but I thought I viewed the backlights being on when the set had no sound/pix. Any thoughts?

[stonoguy]

Re: Samsung LN40E550

I did some more investigating and found on the embossed graphic (main board) by plug CN202(?), the voltages that are supposed to be on the pins of that connector. 5.3v std-by/5.3v/13v were displayed. When I receive that part, and install it, we'll see!

[stonoguy]

Re: Samsung LN40E550

I finally received the replacement part and installed it. The set fired up. When I turned the set on/off, I heard the “chimes”. I also heard the broadcast audio. I did not verify if video was present because the set is face down. When I adjusted the set to view the video, the set would not turn on…dead, AGAIN!
Checked the component I had just installed and sure enuff, it was shorted. D to G – 756 ohms, D to S - .4 ohms, G to S - 756 ohms. ??????????????

[CapLeaker]

Re: Samsung LN40E550

Maybe you got a fake Mosfet, something not right with the gate drive or you have a problem on the 13V rail output. Since all the pins were shorted on the mosfet before, I'd be looking at the gate drive.