Samsung 940n wont turn on

[CroTech]

Before I start typing, I wish everyone merry Christmas and a happy new year...

My problem is I have a "wont turn on" samsung 940n, changed caps except the big one and the small one right next to the connector of the logic board...
Also I changed the inverter transformer since I didnt own a multimeter so I suspected the trafo is dead.

Done that and it still aint working. Just wont turn on.
In the attachments I put the pictures with the measurments of the main and the connector, also I can do any other measurment with the instrument that I put in the attachment if anyone can help me, thx in advance.

[selldoor]

Re: Samsung 940n wont turn on

Ok you say you didnt have a multimeter -Have you got this blue one since then.
If so can you switch it on and say or picture the reading on the meter, then again with the probes together.


Haha - just looked at the pics you are now using the multimeter.

were the boards all connected up when you did the tests


pic could do with being a bit sharper and do not clip the ends of the boards off

[CroTech]

Re: Samsung 940n wont turn on

I said I didnt have the multimeter when I suspected the transformer is dead so i replaced it with a new one... Now I have this blue one and I can measure anything you want me just say what. I´ve put the measurments on the pic in the attachemnt.

And sorry for the low quality images, I dont own a camera, I took pictures with a mobile phone.

[CroTech]

Re: Samsung 940n wont turn on

The logic board was connected to the power board and the power board was connected to the AC. I only did not connect the screen.

[selldoor]

Re: Samsung 940n wont turn on

when it was all connected does the screen flash at all when you switch it on.
What does the power led do.

[CroTech]

Re: Samsung 940n wont turn on

The screen doesnt give any sign of life and neither does the led board with the switches.

[selldoor]

Re: Samsung 940n wont turn on

OK - On the main board there are two voltage regulators. I think the top one may say
on it 1117-18 the other may be ????-33.
Can you test them as per this guide written by retiredcaps - just ask if you dont understand.

[CroTech]

Re: Samsung 940n wont turn on

I tested those transistor looking parts circled in green (see attachment)...

The one right next to the main cap has readings:
pin1 0v
pin2 -108,1 to -108,3V
pin3 (this one goes up and down so i am not sure) goes from -38 to 53V

The one in the top:
pin1 0V
pin 2 4,8-4,9V
pin3 0V

[selldoor]

Re: Samsung 940n wont turn on

I tested those transistor looking parts circled in green (see attachment)...

The one right next to the main cap has readings:
pin1 0v
pin2 -108,1 to -108,3V
pin3 (this one goes up and down so i am not sure) goes from -38 to 53V

The one in the top:
pin1 0V
pin 2 4,8-4,9V
pin3 0V

The measurements are not much use without knowing what the part numbers are - and if you can find a data sheet even better.

There are a lot of tests in this guide again written by retiredcaps which may help you.

https://www.badcaps.net/forum/showthread.php?t=10419 Start at post19 for latest version.

[CroTech]

Re: Samsung 940n wont turn on

sorry, just noticed the one beside the main cap has 6 legs, here is the picture that shows which legs I measured.

pin 1 -110,3 to -110,5v
pin 2 -110,2 v
pin3 -35 to 58V
pin4 108,1v to 113,7V
pin5 -100,8 to -101,3V
pin6 not soldered

The one near main says DH22 DM0465R
supposably http://pdf1.alldatasheet.com/datashe...SDM0465RB.html

The one at the top says EN210A 7525EN
cant find nothing on this one

[selldoor]

Re: Samsung 940n wont turn on

Yes that is the correct data sheet

Any joy testing the voltage regulators - There is no 14v on the power supply
- perhaps because its not getting a start up signal from the main board.

[CroTech]

Re: Samsung 940n wont turn on

The main board? U are refering to the logic board with the VGA connector?

I dont understand are the voltage regulators ok or they sholud be replaced?

I pluged in the logic board and measured the voltages on the 7 pion connector again and there is no change in the measurments.

[selldoor]

Re: Samsung 940n wont turn on

Yes Main board = logic board.

The two regulators provide a steady 1.8vdc and 3.3vdc usually derived from the 5vdc.
These lower voltages are used for signals between the boards.
When you plug in the boards should immediately have 5vdc (which you have on Pin 1 on the connector.) When you press the on button the logic board sends a voltage blip
(usually 3.3vdc) to the Power supply (possibly on PIn7) telling it to start up the higher voltages. (14vdc)

I dont know if the voltage regulators are ok that is why I asked you to test them
in accordance with the guide.

[CroTech]

Re: Samsung 940n wont turn on

The "How to test a voltage regulator" tutorial didnt help me much... I measured the voltages on the pins but those dont mean me nothing since I dont have a reference to match it to... I am ashamed that I am a 3rd year student of electrical engineering and I dont have an idea of how to reseamble a bad voltage regulator from a good one

[selldoor]

Re: Samsung 940n wont turn on

OK First we have to establish what regulator you have. I am relying on you as I cannot see in your picture.

"You can identify a voltage regulator by looking at its part number and finding its datasheet. Some common voltage regulator part numbers are 1117, 1084 and 7805."

So what does it say on yours - We will just work on the top one in your picture.

[CroTech]

Re: Samsung 940n wont turn on

the top one has written:
EN120A
7525EN
and has two simbols for diodes

[selldoor]

Re: Samsung 940n wont turn on

Sorry mis-communication voltage regulators are here

[CroTech]

Re: Samsung 940n wont turn on

The upeer one is 17-18 0743FG
readings:
pin1 0V
pin2 0,08-0,09V
pin3 0,7-0,75V

the lower one is 17-33G
readings:
pin1 0V
pin2 0,7-0,75V
pin3 1,56-1,66V

[CroTech]

Re: Samsung 940n wont turn on

So? Those regulators are both fixed regulators...

suffix 18 which means 1,8V so pin1 + pin2 should give 1,8V and thats not true, so it should be replaced?

suffix 33 means 3,3V so pin1 + pin2 should give 3,3V which is also not true, so it also should be replaced?

Checked the readings a few times and same results

[Rtech]

Re: Samsung 940n wont turn on

To get 3.3v from the reulator,normally means that at least 5v is the input voltage.Therefor is the Power board supplying 5v to the Logic Board,to give that a chance to happen ???,once you get the 3.3v then you should get the 1.8v from the other one.So at the moment there is no certainty that the 1.8 regulator is faulty.