Samsung LN40B630N1F PSU Problem

[landyboy]

I just picked up a Samsung LN40B630N1F that will not power up no lights on the front at all. When I opened it I found the fuse noted below in the picture blown. I replaced the fuse and as soon as I put AC power to the board the fuse blew again. I thin pulled the board out of the inverter sockets and disconnected it from the main board put AC to it and the fuse blew again. With the fuse removed I have around 160vdc volts across the fuse sockets and about 33vdc to ground both sides.

[tom66]

Re: Samsung LN40B630N1F PSU Problem

Schematic
http://www.tgohome.com/ServiceManual...&Search=Submit

Test bridge, diodes, fets, etc.

[landyboy]

Re: Samsung LN40B630N1F PSU Problem

QI820
50 ohms 50 ohms .3 ohms

QI821
39 39 .3

[tom66]

Re: Samsung LN40B630N1F PSU Problem

It's dead, Jim... You'll likely have to replace a few resistors and diodes around them, but it's transformer isolated so the controller IC should be OK.

[landyboy]

Re: Samsung LN40B630N1F PSU Problem

I also tested the Bridge Rectifier

neg lead to pos lug pos lead to ac lugs 1600ohms
same with pos lead on neg lug and neg lead to ac

[landyboy]

Re: Samsung LN40B630N1F PSU Problem

What readings should I see on those two?

[tom66]

Re: Samsung LN40B630N1F PSU Problem

Expected for FET: Open all directions except 2-3 or 2-1 where one diode may be visible in reverse.
Test bridge out of circuit to check it.

[landyboy]

Re: Samsung LN40B630N1F PSU Problem

I found these do you think they are acceptable?
FDPF 7N50 ( 7 AMP) MOSFET UPGRADE FOR FDPF 7N50U (5AMP) MOSFET

[tom66]

Re: Samsung LN40B630N1F PSU Problem

Should be OK.

[landyboy]

Re: Samsung LN40B630N1F PSU Problem

UPDATE: Replace the two above mentioned FETS and set is working great!!

[tom66]

Re: Samsung LN40B630N1F PSU Problem

Nice one! Thanks for feedback.

[ajimetro]

Re: Samsung LN40B630N1F PSU Problem

I had same kind of issue in Toshiba 40AV700E LCD TV.Two FETs are burnt (7N50U) & i could find the FET of 7N50 (not the 7N50U) in my country.So I replaced the two FET s & also Smoothing cap 1000uF/10V are Leak.Then replaced it also
& power up the TV Using 100W bulb replaced with main Fuse.
Its blinks with bright.Then i replaced the fuse & power up.It works for about 30 seconds & burnt the FETs again.Not only that near SMD resistors & Diode are also burnt.Now I couldnt find the values for SMD s.So how may I find the values for that & may i replace the 7N50U with 7N50?

Thanks.

[DV442]

Re: Samsung LN40B630N1F PSU Problem

It's dead, Jim... You'll likely have to replace a few resistors and diodes around them, but it's transformer isolated so the controller IC should be OK.

What should the readings be at Q1820 and Q1821?

[tom66]

Re: Samsung LN40B630N1F PSU Problem

Nearly open circuit all but one way around.

[DV442]

Re: Samsung LN40B630N1F PSU Problem

Hmm, thanks for the info.

It appears that Q1821 is good. But on Q1820 I have readings that are not the same.


Q1821
Pin 1 - Pin 2= .4 ohms
Pin 1 - Pin 3= 1.0 ohms
Pin 2 - Pin 3= 1.1 ohms


Q1820
Pin 1 - Pin 2= .3 ohms
Pin 1 - Pin 3= 32.3 ohms
Pin 2 - Pin 3= 32.3 ohms

Would you say that Q1820 is bad? Thanks for your help!

[rawilson3]

Re: Samsung LN40B630N1F PSU Problem

I am having the exact same issue and the same fuse is blown. Is there a diagram that shows the components tested and expected test values that I could follow to diagnose and repair my set? Thanks for your time and help.

[budm]

Re: Samsung LN40B630N1F PSU Problem

Is your board # is BN44-00264A? If it is then take the resistance readings as shown in post 3~10 and report the readings.

[rawilson3]

Re: Samsung LN40B630N1F PSU Problem

Thanks for the reply. I will double check the model of the board and test if applicable tonight and followup with results.

Thanks!

[rawilson3]

Re: Samsung LN40B630N1F PSU Problem

ok

Q1820

1-2 : 2.6
2-3: 2.0
1-3: 2.6

Q1821

1-2: 1.9
2-3: 1.9
1-3: 2.6

[rawilson3]

Re: Samsung LN40B630N1F PSU Problem

Any ideas if my parts are dead? Should I take any additional readings?

Thanks!