Samsung Syncmaster 932B

[Djadjo]

Re: Samsung Syncmaster 932B

Ok i have the same problem on my 932B panel...the display shows picture and than after one second backlight shuts down...
So i have firstly changed all caps,all new and all are the higher value in voltage..
the ones that was default on the inverter board,all were good...multimeter test
but the problem remains...

I have measured two blue point and red point on the inverter transformator..and both of the point were 1K ohm....so i presume its good
the problem remains...

I have lend from my friend the same monitor and try to figure out are on my panel ccfl tubes gone..but no..i mean i connect his inverter board and the panel works no problem...when i changed video motherboard it works too....
so the only problem lays on my inverter board....

I have come to conclusion that maybe the faulty sense circutry is cause to shut down backlight...

I only think that or SEM2005 or STU309D are faulty....

the ( U201) SEM2005 i cant found...Is there a substitute controler?
the ( U202 ) STU309D i orderd so i wait and give it a try with replacing

is there some other idea what to try

PS: i didnt say but all other components on the board are all measured with multimeter and didnt finde any burnt or too different reading of value...i have compare values with friends working inverter board...

Can i circumvent some pins on sem2005 error line to make it work on purpouse...so the sens will be shortened but it will leave backlight turned on






Thanx

Djadjo

[retiredcaps]

Re: Samsung Syncmaster 932B

So i have firstly changed all caps,all new and all are the higher value in voltage..

What brand and series did you use for replacements? It matters in a SMPS application if you used general purpose caps or low ESR caps.

the ones that was default on the inverter board,all were good...multimeter test

A multimeter will NOT test for ESR (ohms). You can meausure uF, but not ESR with a multimeter.

I have measured two blue point and red point on the inverter transformator..and both of the point were 1K ohm....so i presume its good

What is the exact reading? It should be 3% of each other.

PS. Please use the manage attachments function here to upload your pictures and please do not post inline. I will not look at pictures that are hosted offsite due to unwanted popups.

[Djadjo]

Re: Samsung Syncmaster 932B

The caps i used arent low esr...and they are jamicon brand...maybe not good brand? The original caps from the inverter board wasnt low esr either....

Ok ill easy replace caps to low esr...do you think that it will correct fault?
yes to mention i have resolder all posible solder points pins etc...


Ok i know that multimeter test is not good method to try caps...i can try to measure caps on lcr meter...but if a put new esr than its pointless

red and blue point value is blue 1,03 kOhm and red 1,06 kOhm


Sorry for the photo service...wont happen again...you can freely delete pictures


Tnx

Djadjo

[retiredcaps]

Re: Samsung Syncmaster 932B

The caps i used arent low esr...and they are jamicon brand...maybe not good brand? The original caps from the inverter board wasnt low esr either....

SMPS applications require low ESR caps. Manufacturers make all sorts of different caps: general purpose, low ESR, etc.

I don't know if Jamicon makes low ESR caps or not.

If the caps are on the inverter are the originals, replace them with somethinig like Panasonic FR, FM, or FC (in that order) caps.

red and blue point value is blue 1,03 kOhm and red 1,06 kOhm

What is 1,03 kohm? Is that 1030 or 1003 ohms?

[Djadjo]

Re: Samsung Syncmaster 932B

its 1030 ohm....

i have tried with another mm...and on friends working inverter board
both values are 1010 ohm

and on mine faulty inverter board are 1030 and 1050 ohm....

will try to change/resolder transformator from working to non working board to see em i geting somewhere



Djadjo

[Djadjo]

Re: Samsung Syncmaster 932B

I found out that the trafo went bad...one side is lighting the ccfl..and other dont...and then the feedback sens shuts down the whole inverter...

when i put other but ok trafo...the inverter board works no probl...

looking at ebay the trafo costs around 12usd...and whole inverter board could be found for 20usd....hm


Djadjo

[retiredcaps]

Re: Samsung Syncmaster 932B

If 1010 ohms is the "correct" value, that implies

1010 x 1.03 = 1040 ohms.

1050 ohms would just be enough to make it "bad".

Good job in tracking down the problem.

[Djadjo]

Re: Samsung Syncmaster 932B

When i measured trafo removed from board one side of secundary was 1kilo ohm and one was 1100 ohm wich was obviusly gone bad...Thanks Retiredcaps for
sugestions...I have gone too deep with understanding of malfunction so i have resoldered all ic-s with good ones but the problem was only in trafo...tnx again

[Crauler]

Re: Samsung Syncmaster 932B

Just repaired a Samsung Syncmaster 932B, screen was black, only power button blinking.
There are was 2 bad caps on power board, i determined it by eye:

[PlainBill]

Re: Samsung Syncmaster 932B

Just repaired a Samsung Syncmaster 932B, screen was black, only power button blinking.
There are was 2 bad caps on power board, i determined it by eye:

Good!!! Did you replace the rest of the CrapXons or are you looking forward to opening the monitor up again in a few months?

PlainBill

[waitery]

Re: Samsung Syncmaster 932B

I have this same board and the primary side is solid, but when I go over the secondary side, the voltages are way low and fluctuate rapidly. All but two of the caps are 100%, tested for capacitance and esr. I replaced two of the 1000uf @10v caps with brand new low esr Nichion 1000uf@25v, but am having the same problem. Blue power light is flashing. Any thoughts or suggestions?

[retiredcaps]

Re: Samsung Syncmaster 932B

Any thoughts or suggestions?

1) What is the DC voltage across the big cap? It should be mains x 1.4 or around 165V DC for North America. Is it steady or fluctuating?

2) What is the DC voltage across the startup cap? This cap is usually 22uF 50V or something in that range and is next or close by the biggest cap. Is it steady or fluctuating?

[waitery]

Re: Samsung Syncmaster 932B

Hi Retired,

OK, big cap is 170.8 vdc, very steady, no fluctuations.

Start up cap is 47uf@50v. It measures out at 10.78vdc and is also very steady, no fluctuations.

Thank you for helping me!! What do you reccomend next?

[retiredcaps]

Re: Samsung Syncmaster 932B

What do you reccomend next?

1) What are the DC voltages across the Schottky diodes (on the power board) on the secondary side? Are they stable?

2) If you disconnect the logic board, do the secondary DC voltages stay stable?

3) A picture of your boards much like the ones in post #1 uploaded using the manage attachments feature would help. Please do not post inline. Manufacturers can and have used different layouts, but kept the same model number.

[waitery]

Re: Samsung Syncmaster 932B

OK, measured out with the logic board....14.7 vdc to 15.2vdc, fluctuating rapidly with nothing stable.

Unplug the logic board and it drops down to .75 to 1.25vdc, again fluctuating rapidly nothing stable.

The blue light is pulsing on the bezel in 1 second intervals and nothing on the screen.

I looked the the prior post (pictures in post #26) and that board is the same one that I have. I can take another pic, but it might be redundant. What do you want to see happen?

[alexanna]

Re: Samsung Syncmaster 932B

I think it's time to see some good photos of the front and back of YOUR power supply.
The best way is a straight down overall shot of the board, with no flash, we need to be able to read the writing on the board.
It is suggested not to post inline or off BCNs sight, go advanced on your post and use managed attachments. You will need to resize to less than 2000x2000 p limit.
On the back of the power supply I think its CN201? The pins are identified what do they read?

[waitery]

Re: Samsung Syncmaster 932B

My camera is dead and I can't get pics up right now. Can you give me more to go on in regard to troubleshooting. It is exactly like the board in #26.

[retiredcaps]

Re: Samsung Syncmaster 932B

OK, measured out with the logic board....14.7 vdc to 15.2vdc, fluctuating rapidly with nothing stable.

Unplug the logic board and it drops down to .75 to 1.25vdc, again fluctuating rapidly nothing stable.

I expected to see stable secondary voltages as specified on the power board with or without the logic board plugged in. The pics in post 26 are too out of focus and low resolution to be useful.

There should be a smps pwm chip probably on the backside. It could be defective which causes unstable secondary voltages? Look for a 8 pin IC and list the chip number.

[waitery]

Re: Samsung Syncmaster 932B

Yes, I got it. It has six legs on both sides. It reads: dmo465r

[retiredcaps]

Re: Samsung Syncmaster 932B

Yes, I got it. It has six legs on both sides. It reads: dmo465r

Datasheet at



says 12V DC is required for startup (pin 3 - Vcc). Either the 47uF 50V cap is bad (measuring 10.xx V DC) or the smps controller or circuitry is bad. I'm on a 10 inch netbook and it is midnight so I'm off to sleep, but take a look at the datasheet.

Did you measure the uF and ESR of the 47uF 50V cap? What brand and series is it?