Samsung ln40d550k1fxza

[triplefour]

Re: Samsung ln40d550k1fxza

ok actually i realized the psu and motherboard are good, by hooking up my n64 and changing source till i hear it, and then i used a strong light and i could see the image on the screen, so it seems like my only problem now is getting the backlights to light up. i can see that i am sending 12v to the inverter...hmmm maybe i got lucky and didnt fry anything with that fuse mistake...

[budm]

Re: Samsung ln40d550k1fxza

Which inverter board do you have?
http://www.shopjimmy.com/catalogsear...ln40d550k1fxza
Also check the DC Voltage right at the two leg of the main filter caps when TV is on, it should have >360VDC on the two legs (there are two of them rated at 450VDC).
To blow a 10A fuse, some thing did blown up and blown open circuits that is why it did not blow your new fuse now.

[triplefour]

Re: Samsung ln40d550k1fxza

ok heres some pictures of the inverter, and the connectors on the PSU

voltages to the inverter:
pin / voltage
1 - 4.2v
3 - 4.2v
8 - 0v
9 - 0v
10 - 12v
11 - 12v
12 - 12v

[triplefour]

Re: Samsung ln40d550k1fxza

but the 10A fuse never actually blew. something went pop and i assumed it was the fuse but when i actually checked it later, the fuse was fine...so it was something else...but i am getting all the voltages i need to the motherboard and TCON to transmit the signal to the panel but i am not getting any backlight even though the inverter is getting 12v... i guess the pop could have been something on the inverter going bad. but i really have no idea.

im pretty sure i did check the filter caps while the tv was running and i saw 165v on both of them.

[budm]

Re: Samsung ln40d550k1fxza

"im pretty sure i did check the filter caps while the tv was running and i saw 165v on both of them."
Well, that is the answer, it is not working. As I have indicate in post 22, it should have >360VDC. The PFC Voltage booster circuit is not working, it blew up the first time that why the fuse was blown, you need a new board.

[triplefour]

Re: Samsung ln40d550k1fxza

i know you're the expert but do you think theres a chance you are mistaken about the voltage on these main filter caps? 165 seems pretty normal to me from the other tvs ive been working on...can you please explain how u know they have to be > 360v?

edit: the voltage 4.2 on the low and high is whats the problem, right? that should be 24v and 12v?

is there really no way to repair the damage?

[budm]

Re: Samsung ln40d550k1fxza

"can you please explain how u know they have to be > 360v?" Because it has PFC Voltage booster circuit to raise the 170V to >360VDC. I can see it by looking at the board layout.
"is there really no way to repair the damage?" Things can be repaired, it just how much time and money you want to spend on it.
And if you want to learn about PFC Voltage booster, then just do the research on the subject to get some idea what is it is for and how it works, just matter of spending hours, days, years in learning.

Examples:
You worked on this one, it also has PFC: https://www.badcaps.net/forum/showthread.php?t=40311
Also this one: https://www.badcaps.net/forum/showthread.php?t=40044
Also this one: https://www.badcaps.net/forum/showthread.php?t=39670
You should start taking some voltage readings and take notes on what you work on.

[budm]

Re: Samsung ln40d550k1fxza

BTW, the high frequency/high voltage on pin 1 and pin 3 (white and blue wires) will be in hundreds of AC volt for driving the primary side of the inverter transformers.

http://www.shopjimmy.com/media/catal...40b-bottom.jpg
If it was working, your meter would have been blown up.

[triplefour]

Re: Samsung ln40d550k1fxza

aw man....i thought anything going to the inverter was safe...i thought it only went high voltage after the transformers! jeez...good thing i blew up this tv instead of my meter i guess... so what area of the board is the pfc and what components make it up?

[budm]

Re: Samsung ln40d550k1fxza

OK, you are going to have do some research and will learn about the board, see the bottom side of the board in my post 28, you will see SMD ICs, go look up the spec sheet to see what they are and what they do, this is the way for you to learn.

[Clydeuk]

Re: Samsung ln40d550k1fxza

Just an observation based on a previous comment. You suggested earlier that you feel you may have had a working TV if you had only replaced the blown fuse with the correct 3.15A rather than the 10A fuse you tried. That won't be the case. Sure the 10A fuse did not protect the circuit which resulted in the pop and damage to the PFC circuit, however a 3.15A fuse would just have blown. Had there not been a fault on the power supply other than just an open fuse, the set would have worked when the 10A was put in, albeit you would have had no protection for the circuitry and something could have overheated and caught fire etc etc.

So you had a short on the primary, which correctly blew the 3.15A fuse. By fitting a higher rated fuse you allowed that higher current to flow, the pop was probably the MOSFET in the PFC circuit blowing a hole, or possibly some print vaporising, the short now is probably gone hence why the new fuse holds, but the PFC circuit isn't working.

I do think a replacement board would be the best method as I expect a fair bit of damage will have been done, otherwise you could find yourself in a chicken and egg situation where you replace some parts only to find them blowing again immediately due to other faulty parts still in circuit.

[triplefour]

Re: Samsung ln40d550k1fxza

thank you cylydeuk for your input. what you say makes sense. if it were just about fixing this TV i would definitely order the board but in this case im more interested in using it to learn about the PSU, specifically with this one, the PFC booster circuit. but maybe its a bad one to start with because there may be too many unknowns blown already... i have other PSU's that might be easier. maybe ill just end up selling the motherboard out of this one and be done with it...

[budm]

Re: Samsung ln40d550k1fxza

Well if you want to learn, then you need to get the P/N of those SMD ICs on the bottom side of the board and get the spec sheet and the application notes, those info will explain how each one of those ICs function.

[triplefour]

Re: Samsung ln40d550k1fxza

thanks budm. i will try to do that.

[triplefour]

Re: Samsung ln40d550k1fxza

so i took the board out to study it in detail (try to learn the circuits of this PSU and hopefully others)
right away i figured out where that pop had come from.
the 2 mosfets near the fuse that are both connected to the same heatsink are totally blown apart.
i cant even read the markings on one of them.

what do you think will happen if i just replace these mosfets?

[triplefour]

Re: Samsung ln40d550k1fxza

im starting to think they will just blow up again... i need to figure out why they blew in the first place...

[budm]

Re: Samsung ln40d550k1fxza

Good clear pictures of the bottom side of the board?

[triplefour]

Re: Samsung ln40d550k1fxza

from shopjimmy:

[triplefour]

Re: Samsung ln40d550k1fxza

Any idea what I should look for?

[Shane711]

Re: Samsung ln40d550k1fxza

Just in case anyone comes here with the same problem, their TV won't turn on. Here is what you need to check. First check to see if the fuses are blown and if they are you might need to replace all these parts but at least check them before you spend any money.

LN40D550K1F / LN40D550K1FXZA / 40D550K1F
Board Part Number = BN44-00440B

Transistors ........... QQI802, QQI808, QP801, QP802
Capacitors............ CM806
Fuses.................. FS801S, FS802S
Diodes................. ZDM805, ZDM806
Resistors.............. RI805, RI806, RP825
Integrated Circuits. ICI801, ICM801, ICP801

For Board Part number BN44-00440A check these parts

Integrated Circuits. UI801, UM801S, UP801S
Resistors.............. RM811, RM823, RP821
Transistors............ MI1801, MI1803, Q1801, Q1803, QP801S, QP802S
Diodes................. D1809, D1811, DM801, DM802
Fuses................... FM801S, FS801S

It would not hurt to just replace all these parts if you do not know how to test them but only if you have tested the fuses and found them to be bad.

NEVER replace the fuse without testing or fixing your power supply, it blew for a reason and will only blow again.