Samsung LN40E550

[stonoguy]

Re: Samsung LN40E550

Received the PCB and the set still cuts off then on after playing approx. 5 minutes or so. This is just like previously. Anything else I should check??

[vinceroger69]

Re: Samsung LN40E550

im sorry to hear the replacement board hasnt fixed the issue try taking again the voltages on the psu when the sets working and when its not and post your findings.

[CapLeaker]

Re: Samsung LN40E550

also check the power on the tcon.

[stonoguy]

Re: Samsung LN40E550

I had another unexpected medical emergence (in-law) that called me out of town and away from that HDTV.
I looked at the MOSFET that I had replace and saw that one of the 3 'legs' connects directly to the 5 volt regulator rectifier. I replaced this rectifier and have played this set without any problems since ~ 10AM this morning (no back installed). (4/7). Hopefully this fix will rectify this on/off problem, We'll see! Will let the set play over night and until 10AM on 4/8 and see if any problems arise. Will assemble the set with stand and back and let play for a few hours and see what transpires. So far, so good! Fingers crossed!! Later on!

[vinceroger69]

Re: Samsung LN40E550

Fingers crossed its now fixed it was a odd fault.

[stonoguy]

Re: Samsung LN40E550

Well, I thought it was fixed. Secured all the modules and installed the back & stand. Set played for about 30 minutes and 'poof'!....dead set! I haven't done a thing to this set as I am very 'frustrated' (a nice word for an expletive). Looks as if this is a thermal problem??....any suggestions?

[CapLeaker]

Re: Samsung LN40E550

What exact part did you replace last time and its location (like D104) and with what did you replace it with? Any picture(s)?

[stonoguy]

Re: Samsung LN40E550

Have checked and removed from the circuit the same parts that has been shorted previously....the MDD3752, P channel Trench MOSFET. The set goes dead but doesn't blow any fuse......strange.

[stonoguy]

Re: Samsung LN40E550

Pictures forthcoming.......

[stonoguy]

Re: Samsung LN40E550

MDD3752
P-Channel Trench MOSFET, -40V, -43A, 17mΩ

Can not find this part stocked anywhere I have looked in the USA...Mouser, Digikey....can get them from China.....replaced this with the same component. What is the significance of the negative v & A? Also, have found MDD3752RH.....What does RH mean? Would it be OK to use one of these? Also, this component is soldered to the circuit side of the module....the underside......TO-252 package.

[CapLeaker]

Re: Samsung LN40E550

Did you check the mosfet if it actually is bad? Is there a short to the gate of the mosfet?

[stonoguy]

Re: Samsung LN40E550

Yes, I have…the defective part:

Drain to Source= 0 ohms
Source to Gate = 760 ohms
Gate to Drain = 760 ohms

Shorted for sure!

I am assuming that the data sheet is correct: TO-252

Source is the right leg
The Gate is the left leg
The Drain is the tab.

With the defective component out of the circuit,
I found that the connection where the Source
is soldered, reads ~ 3M ohms…..drops to ~ 4K ohms
then increase again…...capacitor influence??

[TechGeek]

Re: Samsung LN40E550

Sounds like a capacitor receiving voltage from the multimeter probes.

[stonoguy]

Re: Samsung LN40E550

I know that Digikey nor Mouser do not have MDD3752......The link to Newegg have them. They are from UTSOURCE. This is where I purchased the ones I have now. The description says these components are REFURBISHED.....huh? I never heard of a refurbished transistor!

[CapLeaker]

Re: Samsung LN40E550

maybe a working pull?

[stonoguy]

Re: Samsung LN40E550

I am still out of town (In-laws medical)...no access to TV......since I am retired, I am the choice for my "services"! I will return (hopefully) soon! Thanks for the previous help!

[stonoguy]

Re: Samsung LN40E550

I am FINALLY back home!! Have soldered a new MOSFET to replace shorted one. Also replaced 13 volt regulator. Will give update on set progress....have a bunch of yard work to do.....

[dick_barton]

Re: Samsung LN40E550

MDD3752
P-Channel Trench MOSFET, -40V, -43A, 17mΩ
.What does RH mean? Would it be OK to use one of these? Also, this component is soldered to the circuit side of the module....the underside......TO-252 package.

It's a P Channel Mosfet so is a negative channel device. -40V means max voltage -40V (minus) and max current through device -43Amps (minus).

N Channel Mosfet is positive channel device so would be +40V @ +43 Amps

P and N Channel devices operate on reverse supply voltages.