Samsung LN40E550

[stonoguy]

Re: Samsung LN40E550

I stumbled upon this bit of info.....the MOSFET: MDD3752 (Samsung part # BN81-04764A) IS NO LONGER AVAILABLE. This may be why I could not find on Mouser or any of the other places I looked....except for Amazon. These parts I received, came from China! I thought they were pretty inexpensive......Anyway, I ordered all of the filters on the PS board. I got them from Digi-Key. One of those caps connects directly to the drain of the MOSFET that I replaced. With the part removed, the resistance from ground (cold) to the drain was 543 ohms; g - 8.18M ohms; s - 6.53M ohms. Maybe that cap is leaking.....????? I'm am digging to see if there is a part that is a replacement or one that has the same charcteristics of the shorted MOSFET. Any suggestions?

[stonoguy]

Re: Samsung LN40E550

I am at a quandary.....the parts' ID on the PCB does not NOT match the ID on the schematic.......I have never run into this.....if a part needs replacing, I have always replaced the defective part with the one that came out (MDD3752)(Unless a factory bulletin suggested otherwise). The shorted part that was replaced with the same type that came out...but that part # on the schematic is a KA431SAMF2. The MDD3752 is a TO252 envelope, while the KA431SAMF2 is SOT-23F. I am going to replace ALL of the capacitors on the PS board and install one of the MDD3752 & then see what voltages are present on various spots on the PSBs. Opinions? Suggestions?.....Anyone?....Anyone?

[stonoguy]

Re: Samsung LN40E550

OK....I replaced all of the filter caps on the power supply board and installed a new MOSFET to replace the one that was shorted.....the set plays OK...audio/video OK. The original problem (set cutting off/on) has re-appeared. Appears to do this after set plays for about 5 minutes or so. I have a can of component cooler and have tried cooling down the various components mounted on heat sinks...no luck. I sprayed the MOSFET I replaced...no luck. I sprayed a few of the axial diodes, as well...still no luck. The ~400vdc (hot ground) drops very little when the set is off. The 5.3v (DM806 on board) drops to 1.3v & the 13.1v (DM802 on board) drops to 4v but gradually increases to 13v and the set then turns on.

[stonoguy]

Re: Samsung LN40E550

Maybe I should clarify the sequence of the on/off problem I m havig with this set.

When first turning 'on' the set, it will play OK.

After about 25 to 30 minutes the set cuts 'off'. No audio, no video & back lights
are off.

After about a minute or 2, the set cuts back to 'ON". By this I mean that the 'ON chines' are heard, the videa, the audio and the backlights are all functioning. This remains the case for a few minutes then this process starts over...It will continue to repeat these actions until the power is removed.
When the set fires uo, it's like the set was turned on with the remote or frot panel switch bbutton.

[CapLeaker]

Re: Samsung LN40E550

When it cuts of, does PSon disappear? If it does, there is a problem with the main board.

[stonoguy]

Re: Samsung LN40E550

I measured the dc voltages on the pins of CN802….Ths ribbon cable runs from PS board to main board.

Here's what I found:

ON OFF

PIN 1 B13V 12.8V 0V
PIN 2 P_DIM 4.29V 0V
PIN 3 B13V 12.8V 0V
PIN 4 N/C
PIN 5 B13V 12.8V 0V
PIN 6 BLU_ON 5.13V 0V
PIN 7 B13V 5.13V OV
PIN 8 Ground 0V OV
PIN 9 Ground 0V 0V
PIN 10 Ground 0V 0V
PIN 11 B5V 5.1V 0V
PIN 12 A5A 5.15V 0V
PIN 13 B5V 4.29V 0V
PIN 14 PS_ON 3.44V 0V*


*Voltage drops steadily to 0 volts when set is shutting down.
When the voltage reaches 0 volts, the voltage steadily begins to rise until it
reaches 3.4V...at which time,the set turns.

[stonoguy]

Re: Samsung LN40E550

The first voltage is when the set is 'on', the 2nd voltage is with the set 'off'.

[stonoguy]

Re: Samsung LN40E550

Pin 7 B13V should read 12.9v on 0v off.......

[stonoguy]

Re: Samsung LN40E550

Does this PSon voltage generated on the main board? On the schematic I have, it appears that PSon is coming from Pin 18 on plug CN802. The connector on the board I have has only 14 pins.....The PSon voltage is labeled on the PS board as being on Pin 14....On the main board CN802 the 14 pin connector, would it be on Pin 2 (SW_P), Pin 10 (SW_I) OR Pin 14 (PWM)?

[CapLeaker]

Re: Samsung LN40E550

PSon is generated on the main IC of the main board. So either the easy is getting a new main board, or try fiddling around with the old one, by trying to convert it do a manual PSon.
Did you measure the PSON on the ribbon cable that goes between PSU and main board?

[stonoguy]

Re: Samsung LN40E550

No, but I will ASAP...........

[stonoguy]

Re: Samsung LN40E550

OK.......went out of town unexpectedly...back now, and found when the set goes down (off), the PS_ON goes to zero volts from ~3.4vdc.....you say the main board is defective?

[stonoguy]

Re: Samsung LN40E550

I measured the PS_ON voltage on the power supply board.

[stonoguy]

Re: Samsung LN40E550

What reliable repair outfit would y'all recommend when obtaining a board?....exchange price, correct? How exactly would that work?.....Pay full price for board and when the site receives the dud, you receive a refund for the dud exchange?

[vinceroger69]

Re: Samsung LN40E550

Where are you it dosnt say in your profile and can you post again the board details your looking for.

[stonoguy]

Re: Samsung LN40E550

OK….here is the info:

Greer,SC USA

SAMSUNG #: BN97=06387P (on sticker) _ BN41-01704 (embossed on board)

[vinceroger69]

Re: Samsung LN40E550

http://www.ebay.ca/itm/Samsung-40-LN...item2597096803

[stonoguy]

Re: Samsung LN40E550

OK.......ordered this board.......hope this corrects the on/off problem.......

[vinceroger69]

Re: Samsung LN40E550

OK.......ordered this board.......hope this corrects the on/off problem.......

Hopefully it will sort the problem that seemed a resonable price for the board and looks like it matched all your numbers ive never really had any issues with ebay sellers any problems i have ive always been issued a refund etc.

[stonoguy]

Re: Samsung LN40E550

I am hoping so, as well!! I guess replacing a PCB is quicker and more cost effective than the time it would take a TV shop tech to troubleshoot and repair a set. Also, it takes little knowledge about electronics to follow a flow chart and then replace a board! $$$$ talks!