Samsung LN40E550

[stonoguy]

Re: Samsung LN40E550

The connections/connectors were in place......took readings from the "foil" side of the board.

[budm]

Re: Samsung LN40E550

The connections/connectors were in place......took readings from the "foil" side of the board.

Well if all the boards are connected, you are not even getting the STBY 5V. You do have AC power to the board, right?
Meter set to DCV?

[stonoguy]

Re: Samsung LN40E550

Those readings ARE with the connectors secured....???? (cold ground)

[stonoguy]

Re: Samsung LN40E550

Yes, AC connected......utilizing a variable isolation transformer set to 120 VAC.

[budm]

Re: Samsung LN40E550

Check the DCV right between the two legs of the main filter cap again to see what you have, it should be around 160VDC.

[stonoguy]

Re: Samsung LN40E550

Yep!.......163 VDC.

[stonoguy]

Re: Samsung LN40E550

I need some more checking and found a semiconductor shorted....looked up and was told this item (MDD3752) was a MOSFET. Trying to determine what circuit this thing is in and if anything associated with it, is bad too.

[stonoguy]

Re: Samsung LN40E550

I ordered the shorted MOSFET...appears to be some type of regulator? The schematic I have for this board isn't right.....FYI,,,just by accident I discovered that the schematic is being used for another Samsung power module also...different part number than the board I have....same schematic, though! I was surprised to find that this part being shorted didn't blow any of the fuses....This set was manufactured in 2014, should all of the power supply caps be replaced? They do not look bloated.

[budm]

Re: Samsung LN40E550

I need some more checking and found a semiconductor shorted....looked up and was told this item (MDD3752) was a MOSFET. Trying to determine what circuit this thing is in and if anything associated with it, is bad too.

Can we see the pictures of this shorted part?

[stonoguy]

Re: Samsung LN40E550

Yeah, you can! Charging battery for camera & will download pix ASAP!

[stonoguy]

Re: Samsung LN40E550

OK...here it is!! It was soldered on the foil side of the board. The only one that was on the board.

[budm]

Re: Samsung LN40E550

What section of the board is this part in?
Shorted Source pin to Drain pin?

[stonoguy]

Re: Samsung LN40E550

This component is shorted on all 3 of the connections......shorted to each other.

[budm]

Re: Samsung LN40E550

That is a Power MOSFET used as a switch to provide switched 13VDC on connector CN802 PIN 1, 3, 5, 7.
For that to shorted out you need to check the resistance be tween CN802 pin 1 and GND the main board connected to see if it shows very low resistance.
BTW, that should not stop the board from producing the STBY 5V at CN802 PIN 13.

[stonoguy]

Re: Samsung LN40E550

Just looked @ your last post....will do ASAP......FYI: found two transistors that (I thought were shorted E to B, circled yellow in attached pix). Removed one of the transistors from the board, & it measured good. Checked the connection points and found the E/B had a reading of .1 ohms. The other xtransistor checked the same. Collector(s) to ground, OK.>

[stonoguy]

Re: Samsung LN40E550

BTW. What does the SMD printed om the board mean? Have seen this on the board and in other posts.

[stonoguy]

Re: Samsung LN40E550

OK.... CN802 pin 1 shows 545 ohms....

[budm]

Re: Samsung LN40E550

Just looked @ your last post....will do ASAP......FYI: found two transistors that (I thought were shorted E to B, circled yellow in attached pix). Removed one of the transistors from the board, & it measured good. Checked the connection points and found the E/B had a reading of .1 ohms. The other xtransistor checked the same. Collector(s) to ground, OK.>

Those two in the yellow circles are Dual rectifier Common Cathode, the two outside Pins are Anodes which are tied together to form two diodes in parallel.

[stonoguy]

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.

[stonoguy]

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.