Samsung Syncmaster 2333SW Flickering

[Mr Bill]

Re: Samsung Syncmaster 2333SW Flickering

What reading are you getting from U102 U101 on the main board and what are the labels on the top of them?

U101:
AS1117L-33, 5.04Vin with 3.300v out

U102:
AS1117L-18, 3.287Vin with 1.805v out

I'm a little confused with u102. Assuming i'm looking at the datasheet corectly u102 should have a input voltage of 5v and i'm only getting 3.287 but the output voltage is correct.

[Jasgriff]

Re: Samsung Syncmaster 2333SW Flickering

What reading are you getting from U102 U101 on the main board and what are the labels on the top of them?

[Mr Bill]

Re: Samsung Syncmaster 2333SW Flickering

My meter doesn't have an ac millivolt function. I recapped the entire power supply including the big one and the backlights now stay on solid but i'm not getting an image in regular windows. If i use the keyboard and shut the computer down blindly i get a brief flash of the shutdown screen. If i restart the computer in safe mode i can get an image but it is grainy at the bottom around the task bar but the grainy image comes and goes. I'm thinking it has to be something in the mainboard now but i don't know which direction to go other than finding a used good ebay board.

[budm]

Re: Samsung Syncmaster 2333SW Flickering

What Iam trying to find out is the AC voltage on that large DC main filter cap in the hot side of the power supply, so when you put the meter on AC mode, then put the two probes of the meter on the two legs of that large cap, it should show some AC reading since the rectified DC will not be PURE DC, it will always have some AC component riding on top of the DC voltage. Using the true RMS meter, I do not expect the AC value to be more than 5~10% of the DC reading with load, see the pictures.
AS you can see, when the monitor is not on (but still plugged into the outlet) you can see that the AC ripple is in millivolt range, and less than 5% when the monitor is on with the lamps lit.
This test will not work on the DC side of the switching power supply since most DMM cannot read AC with anything higher than 10KHz, most are made for AC 60Hz reading.
I use this in the field when I do not have a scope handy with me.

[retiredcaps]

Re: Samsung Syncmaster 2333SW Flickering

In a/c mode with the red probe on the positive and the black probe on the negative i am getting between 2.572 to 2.610 volts a/c

On my working Benq 17 inch monitor that I keep "open" for testing, I get 157.6V DC rock solid across the large capacitor. I get roughly 55 millivolts AC across the large capacitor. With the backlights on, I get about 1.667V AC.

[Mr Bill]

Re: Samsung Syncmaster 2333SW Flickering

This is what budm is interested in though. Do you have a feature like min/max on your multimeter?

The only thing that i am aware of with this meter is moving the decimal point from 0.000 to 00.00 or 0000 ect ect.

I first made the decimal disappear (0000) and i was getting 2-3. So then i moved the decimal to 0.000. In a/c mode with the red probe on the positive and the black probe on the negative i am getting between 2.572 to 2.610 volts a/c

[retiredcaps]

Re: Samsung Syncmaster 2333SW Flickering

When i put the red probe on the positive leg and and the black probe on the negative leg the meter was bouncing.

This is what budm is interested in though. Do you have a feature like min/max on your multimeter?

[Mr Bill]

Re: Samsung Syncmaster 2333SW Flickering

Put your meter in AC volt mode and take a reading of the voltage on that large cap again, I want to know what the AC ripple is on that cap.

When i put the red probe on the positive leg and and the black probe on the negative leg the meter was bouncing. I then put the red probe on the positve leg and the black probe on a ground point on the power board and then it gave me a stable reading of 69.3 volts ac.

[budm]

Re: Samsung Syncmaster 2333SW Flickering

Put your meter in AC volt mode and take a reading of the voltage on that large cap again, I want to know what the AC ripple is on that cap.

[Mr Bill]

Re: Samsung Syncmaster 2333SW Flickering

If the large electrolytic (lying on its side) filter cap is 275V, then it implies there is no PFC involved. PFC can boost the voltage to greater than 300V DC which means the large filter cap should be 400V or higher.

The 275 is the yellow cap i put a square around.

If you are getting fluctuating voltage of 153.9 to 159.9V DC, then the large filter cap could be bad without bloating. It should be a solid 170V DC if your AC is 120V AC. On the mega Samsung 245BW thread a fluctuating large filter cap was responsible for flickering on the screen as found by user Aruba..

Its not bouncing around but more 153 with the backlight on and 159.9 backlight off. Its almost like the backlight is pulling the voltage down from load. I did try to read the mega thread but never made it that far (my eyes and brain weren't cooperating )

edit: You can measure the DC voltage on the bridge rectifier to see if the voltage is stable or not.

I checked the bridge rectifier and i'm getting the same result as the large cap, 153 backlight on and 159 backlight off.

There is what looks like a couple voltage regulators by the inverter transformers. I haven't googled the numbers on them to see and i also haven't checked the voltages on them yet.

[retiredcaps]

Re: Samsung Syncmaster 2333SW Flickering

I'm also only getting 153.9 - 159.9 on the large capacitor. Is it not suppossed to be higher when the power supply is hooked up and working (showing a picture)? In the 400 volt range? The filter cap is a 275v btw.

If the large electrolytic (lying on its side) filter cap is 275V, then it implies there is no PFC involved. PFC can boost the voltage to greater than 300V DC which means the large filter cap should be 400V or higher.

If you are getting fluctuating voltage of 153.9 to 159.9V DC, then the large filter cap could be bad without bloating. It should be a solid 170V DC if your AC is 120V AC. On the mega Samsung 245BW thread a fluctuating large filter cap was responsible for flickering on the screen as found by user Aruba.

edit: You can measure the DC voltage on the bridge rectifier to see if the voltage is stable or not.

[Mr Bill]

Re: Samsung Syncmaster 2333SW Flickering

I referred to the filter caps on the logic board.

There are 6 caps on the main board. I measured the voltage at each cap with the monitor on and hooked up to the test computer.

100uf 16v Jamicion TK series -- I'm getting 3.298v
100uf 16v Jamicion TK series -- I'm getting 4.86v

22uf 16v Jamicion TK series -- I'm getting 3.294v
22uf 16v Jamicion TK series -- I'm getting 1.805v
22uf 16v Jamicion TK series -- I'm getting 1.799v

220uf 10v Jamicion TL series -- I'm getting 4.99v

This was with the red probe on the positive leg of the cap and the black on the negative.

[budm]

Re: Samsung Syncmaster 2333SW Flickering

I referred to the filter caps on the logic board. There should be a bunch of DC filter caps on the logic board.
That yellow cap is on the hot side (LINE VOLTAGE) it should have 120Vac on its two legs, be careful on the hot side of the board!
I f the AC feeding the monitor is 120vAC, then the DC on that cap should be 120 x 1.414 = 169VDC.

[Mr Bill]

Re: Samsung Syncmaster 2333SW Flickering

There should be some voltage regulator (3.3v, 1.8, etc) on the logic board and also filter caps, did you check the voltages of those regulators?

There are 2 voltage regulators on the logic board. The 1.8 reads 1.805 and the 3.3 reads 3.292

Is the filter cap the yellow box directly behind the power outlet? If it is, i'm only getting 72.5 - 74.6 with the monitor on (hooked up to test computer)and its doing its usual backlight on/off. I'm also only getting 153.9 - 159.9 on the large capacitor. Is it not suppossed to be higher when the power supply is hooked up and working (showing a picture)? In the 400 volt range? The filter cap is a 275v btw.

[budm]

Re: Samsung Syncmaster 2333SW Flickering

There should be some voltage regulator (3.3v, 1.8, etc) on the logic board and also filter caps, did you check the voltages of those regulators?

[Mr Bill]

This monitor is acting strange. I'm not sure where to start but i'll try my best.
When the monitor is first plugged with no soure it shows "seaching for signal". It will show this for 20 seconds or so until the backlight turns off and it goes into standby, just like normal. Hook the test pc up to it and it will show the bios and all the boot screens. Once windows starts it will briefly display my background then the screen goes black but the ccfl bulbs are still lit up. It will not show the desktop but it will show my screen saver but it flickers. While it's flickering sometimes the backlight will turn off but then back on. I pulled a few sets of used bulbs and it does the same thing with them. It also seems the screen saver is running slower than normal. It does this with the vga-d connector and the dvi-d. Now, if i run the computer in safe mode (600 x 800) it will show windows but it is choppy and still does the flickering. It also is splitting the screen meaning mirroring it.

I tested the voltage regulators on the mainboard and timing control board and they are all in tolerance. The connector going from the power supply to the mainboard has a few voltages i could check:

1)Vcc 5V -- i'm getting 5.06v
2)on/off -- i'm getting 3.291v
3)brightness -- i'm getting 3.263v

The caps on the power supply are a mixed bag of :
Su'scon SG & SH series
Samxon GK series
Lelon RZD series

The caps on the mainboard are:
Su'scon SK series
Jamicon TK & TL series

So the big question is.....Mainboard or tcon?

I don't know if a bad cap could cause this issue but i figured i would see if anyone has had any experience with this symptom. I am also curious to see if i am beating a dead horse.