Samsung 2253BW inverter problem.

[FrankMtl]

Hi, this is my first post.
I repaired a few LCD as a hobby before.
But this Samsung is a difficult one.
I replace all the caps (10) and still nothing on the screen.
All I have is the blue power led.
I test the diodes and they check ok.
What could it be?
I can hear a small squeal when I put my ears close
to the board. The squeal appears to come from the 2 transformers ?
And when I turn on the monitor the squeal goes away.

Thanks.

Frank.

[budm]

Re: Samsung 2253BW inverter problem.

Any good clear pictures of the bottom side of the board?
Did you check green fuse next to one of the inverter transformer?

[FrankMtl]

Re: Samsung 2253BW inverter problem.

Hi, no I didn`t check that fuse.
I learn something today, I didn`t know that was a fuse.
I didn`t check the other T3 fuse either..

Can I check it on the board?
I check my diodes on the board and was able to read them, but from what I read it`s not the best way to do it.

Wich function do I use on my multimeter to check it?
My multimeter is really basic and doesn`t have continuity on it... not good...
Can I use the diode function to test the fuse?

Thanks.

[budm]

Re: Samsung 2253BW inverter problem.

Ohm mode, no power to the board.
Touch your meter probes together so it will show the reading on the meter, it should be <1 Ohms, now put the meter probes on each end of the fuse, it should show the same reading as when you touch the two probes together.
I do not use continuity for testing fuse since the meter will beep with resistance as high as 50 Ohms or more. The fuse may have high resistance but may not be completely open circuit. Continuity does not tell you if you have good connections between point A and point B, it just tells you you have connections.

[FrankMtl]

Re: Samsung 2253BW inverter problem.

Thanks, I set my meter at 200 Ohm and touch the probes together
it gave me 00.3. When I test the fuse with no power on board
it gave me 140.33 something high like that??

Strange I just retest 5 minutes after my post and now it reads 1.
..
Now it read 139.8 ..

I should mention that my multimeter is manual not auto range.

Thanks.
Frank.

[FrankMtl]

Re: Samsung 2253BW inverter problem.

Hi, I bought I glass fuse 4A to replace that green fuse.
Now even the power led doesn`t work?
Can I replace this type of fuse with a glass fuse?
Both are 4A.

Thanks.
Frank.

[budm]

Re: Samsung 2253BW inverter problem.

The original green fuse has blown for reason, more likely that you have bad power MOSFETs (the two 8-pin SMD on the bottom side of the board) which drive the inverter transformer.

[FrankMtl]

Re: Samsung 2253BW inverter problem.

I see, youre correct I tested the green fuse and it showed 1. on my multimeter.
But could it be me that blow it with the heat from my soldering iron?
I see the 2 mosfet that you are talking about, I don`t think I have
the soldering iron to do this. This is so small.
Maybe I will buy another power supply.

Thanks.

Frank.

[Joe Black]

Re: Samsung 2253BW inverter problem.

If you have not gave up yet, check the "transistor-like"components fitted on the metal "radiators".
Those are the power mosfets, and small SMDs that you got afraid of actually drive them-tell them how fast to switch.

Anyway, you should read the model of MOSFETs, and google their multimeter readings.

Most likely, one has failed. Report back with results.

Never just replace fuse, or even a MOSFET for that matter. We should always check WHY something has failed, and act accordingly.

note: not an expert. I stand corrected for anything I state wrong, of course not intentionally. Also, sorry for bad grammar.

edit:
If all MOSFETs test OK (out of circuit) check graetz bridge, and any diodes you may overlook.
Maybe that C113 was there, and you forgot to put another one?

[FrankMtl]

Re: Samsung 2253BW inverter problem.

Hi, don`t worry there were no caps in C113 :-)
This is not my first LCD repair but the hardest for sure.
Well at least I`m learning.
Can I test MOSFEST`s on the board? Or do I have to remove them?
To be sure you are talking about the 3 black thing with 3 legs?

Thanks.

Frank.

[FrankMtl]

Re: Samsung 2253BW inverter problem.

Hi, here is what I found 2 transistors MBR20100CT
and one FET DMO565R.
So they are not MOSFET ?

Thanks.
Frank.

[budm]

Re: Samsung 2253BW inverter problem.

The MOSFETs that you need to check are those two SMD one, the fuse feeds those two MOSFETS so the problem is not in the main power supply section. If you remove that fuse you just install then you should have your power LED back on.

[FrankMtl]

Re: Samsung 2253BW inverter problem.

Thanks, you mean the 2 8 legs chip under the board right?
Label STM8309 ?
I don`t think I can solder this , it`s to small.

Frank.

[stj]

Re: Samsung 2253BW inverter problem.

you can,
put some solder across the pins on one side,
slide the iron up and down the pins while gently levering it up from the side wih a blade.
once it lifts a bit, remove the solder wih some braid and do the other side the same way.

[FrankMtl]

Re: Samsung 2253BW inverter problem.

Hi, I`m more worried about soldering a new chip.

Frank.

[stj]

Re: Samsung 2253BW inverter problem.

put it on the same way and remove excess with braid if your iron is big.

[FrankMtl]

Re: Samsung 2253BW inverter problem.

Thanks for the tip.

[budm]

Re: Samsung 2253BW inverter problem.

You can check the resistance between S pins and the D pins of the MOSFETs with Ohm meter to see if they show low Ohms readings.

[Joe Black]

Re: Samsung 2253BW inverter problem.

Ugh, sorry if I confused you, Frank.
I promise I won't post anymore while leaving to work

So, using the datasheet that budm neatly attached, locate (S)ource and (D)rain pins. Normally, Ohm resistance between those is infinite. If shorted (low Ohms), MOSFET is gone.

Also, I have developed a habit of resoldering inverter transformer pins on every board I get to. It's generally good idea to carefully examine solder joints on all components and check for cracked or insufficient solder joints.

[FrankMtl]

Re: Samsung 2253BW inverter problem.

Hi, thanks , I check to the MOSFET and one shows 0.06 between the S and D pins
The other Mosfet shows 123 between the pins, So I guess this one is gone?
Now I might try to solder this, first I have to google it to see how much is it.

Thanks.

Francois.