Samsung SyncMaster 226BW

[mastertheknife]

Re: Samsung SyncMaster 226BW

Here is a picture with the possibly bad resistor.
Any ideas what else to check\try?

mastertheknife.

[jetadm123]

Re: Samsung SyncMaster 226BW

I found a bad resistor on the power pin going to\from the signal board, on the good board it measures 91,000 ohms and on the bad board around 350 ohms.
Can this be the cause of the issue?

mastertheknife

When you say "power pin", do you mean the one labeled 13V? As for the resistor in question, there should be some numbers stamped on it. What are they. Also, there's a transistor Q201? next to it. With your meter, check it for shorts.

[mastertheknife]

Re: Samsung SyncMaster 226BW

When you say "power pin", do you mean the one labeled 13V? As for the resistor in question, there should be some numbers stamped on it. What are they. Also, there's a transistor Q201? next to it. With your meter, check it for shorts.

Hi jedadm123,

The 13VDC pin is a different pin and can be seen as jumper fuse F301, next to the pin in the center of the picture.
I'm not sure what this power pin means either, its a wire going\coming to\from the signal board, probably to tell the inverter to fire up. Its pin 9 on the connector to the signal board.
Printed on the board:
Pin1 = PWM-DIM (?)
Pin2,3,4 = GND
Pin5,6,7 = 13V
Pin 8 = A-DIM (?)
Pin 9 = ON/OFF

Q201 has no shorts on its pins.

EDIT: Unlike some other resistors on the board, this one doesn't seem to have anything printed on it, its brown though.

Thanks again,
mastertheknife.

[jetadm123]

Re: Samsung SyncMaster 226BW

I found a bad resistor on the power pin going to\from the signal board, on the good board it measures 91,000 ohms and on the bad board around 350 ohms.
Can this be the cause of the issue?

mastertheknife

Okay, a few things to mention. Look a little more closely at the resistor you suspect is bad. I see that the silkscreen on the board identifies it as C201, which means that it's actually a capacitor ("C" stands for capacitor). As for the value, I don't know, since no values are stamped on it.

You mention that this cap is connected to the on/off pin (pin 9). Well, this pin controls the on/off function of the backlight, which could be causing the problems you're seeing.

Off to the right of the suspect cap is the CCFL controller chip (I think it's 20 pins). What is the part number of the controller chip? Also, try and determine which pin the suspect cap is connected to on the controller chip.

Lastly, C201 could be bad, but other components could be bad, which can cause the discrepancy in readings between your "good" and bad boards for C201.

[mastertheknife]

Re: Samsung SyncMaster 226BW

Okay, a few things to mention. Look a little more closely at the resistor you suspect is bad. I see that the silkscreen on the board identifies it as C201, which means that it's actually a capacitor ("C" stands for capacitor). As for the value, I don't know, since no values are stamped on it.

You mention that this cap is connected to the on/off pin (pin 9). Well, this pin controls the on/off function of the backlight, which could be causing the problems you're seeing.

Off to the right of the suspect cap is the CCFL controller chip (I think it's 20 pins). What is the part number of the controller chip? Also, try and determine which pin the suspect cap is connected to on the controller chip.

Lastly, C201 could be bad, but other components could be bad, which can cause the discrepancy in readings between your "good" and bad boards for C201.

The CCFL chip is almost impossible to read because of some glue on it or something. I tried to rub it with alcohol but its almost impossible to read. Its probably OZ964 like someone else posted in this thread. Im only able to see the end of the first line and the beginning of the second line, which makes me believe its also OZ964, i think its a OZ964DN according to the last letters on the first line.

Pin 3 seems to be responsible for the on\off according to the datasheet but i was unable to locate which pin is pin 3.
The datasheet is here: http://www.alldatasheet.com/datashee...2/OZ964GN.html

After cleaning the chip with alcohol, that suspected bad capacitor\resistor measured 84Kohms, strange enough. I closed the monitor quickly and fired it up, with the monitor off, the screen was all white and the backlight was working for about 6 seconds, then began to flicker and turned off.

I checked the resistor\capacitor right after and it was back to 350 ohms.

I will i should try reflowing the solder connections on all solders on the board, maybe that will help.

[mastertheknife]

Re: Samsung SyncMaster 226BW

After reflowing the solder connections around that bad resistor\capacitor, it measured between 91Kohms to 93Kohms (probably depends on the temperature) which is like the other board.
Plugged it in and saw it searching for analog\digital with backlight on. I turned it off, monitor showed a white screen but a different one this time, it had some buzzes\just unstable.
after few seconds the backlight turned off again.
Is it a good idea to reflow solder on all board connections?

Thanks again,
mastertheknife.

[mastertheknife]

Re: Samsung SyncMaster 226BW

Okay i made some nice progress!
I noticed the transistor next to that bad resistor had constantly changing values, while on the good board i measured 190Kohms between one of the legs and the resistor\capacitor.
By reflowing solder on some components and cleaning any residue with alcohol, its pretty much stable at 184Kohms now, close enough to the other board.

The white screen problem is GONE and the monitor indeed stays off when it needs to be off. Also, the backlight doesn't flicker anymore, but turns off about 1 seconds after turning on the monitor.
The interesting thing is, if i hit the "source" button, the backlight comes on another econd and then turns off. Turning off and on the monitor also brings the backlight working for about 1 second and then its off again.

EDIT: Just verified that the problem comes from the power supply board by using the good board on this monitor (the monitor works perfectly with the good board from another 226BW)

Any ideas\clues?
mastertheknife

[PlainBill]

Re: Samsung SyncMaster 226BW

Okay i made some nice progress!
I noticed the transistor next to that bad resistor had constantly changing values, while on the good board i measured 190Kohms between one of the legs and the resistor\capacitor.
By reflowing solder on some components and cleaning any residue with alcohol, its pretty much stable at 184Kohms now, close enough to the other board.

The white screen problem is GONE and the monitor indeed stays off when it needs to be off. Also, the backlight doesn't flicker anymore, but turns off about 1 seconds after turning on the monitor.
The interesting thing is, if i hit the "source" button, the backlight comes on another econd and then turns off. Turning off and on the monitor also brings the backlight working for about 1 second and then its off again.

EDIT: Just verified that the problem comes from the power supply board by using the good board on this monitor (the monitor works perfectly with the good board from another 226BW)

Any ideas\clues?
mastertheknife

Quite a few. First of all, you are really putting a lot of effort into this, and making good progress. Feel free to give yourself an attaboy (lower case, you don't have it working perfectly yet).

The remaining problem is 'two seconds to black. Ordinarily I would suggest testing the CCFLS by hooking up a known good panel. However, what you've described so far screams of contamination on the circuit board. I'd suspect someone spilled something into the monitor. I'd suggest first verifying the BL_ON signal stays high when the backlights go off - that will confirm 'two seconds to black'. Then scrub the board thoroughly with alcohol and dry it completely before testing it.

PlainBill

[mastertheknife]

Re: Samsung SyncMaster 226BW

Quite a few. First of all, you are really putting a lot of effort into this, and making good progress. Feel free to give yourself an attaboy (lower case, you don't have it working perfectly yet).

The remaining problem is 'two seconds to black. Ordinarily I would suggest testing the CCFLS by hooking up a known good panel. However, what you've described so far screams of contamination on the circuit board. I'd suspect someone spilled something into the monitor. I'd suggest first verifying the BL_ON signal stays high when the backlights go off - that will confirm 'two seconds to black'. Then scrub the board thoroughly with alcohol and dry it completely before testing it.

PlainBill

Thank you PlainBill,
I just feel like trying my best to get it to work, before buying another board for $30 on ebay.
I believe the source of all problems was my flux. During soldering one of the capacitors,i accidently spilled too much flux. I assume the flux is causing shorts and im testing many components on the board with my multimeter and comparing to the other board, most match, but those who don't usually do match after some rubbing with alcohol or reflowing the solder.
So maybe there is nothing wrong with this board, in fact it was working good before replacing the capacitors, except that it was flickering when it was cold until the monitor was warmed up.
The CCFLs are good, i hooked up a power supply board from another 226BW and the monitor was working perfectly.
I will check the BL_ON thing.

I am trying to clean the board with alcohol, but the alcohol leaves white marks after drying up and doesn't seem to really remove any shorts caused by the flux spill during my soldering of one of the capacitors near the inverter IC.

Any tips for good cleaning? Is it safe to use a brush on this? it might knock off a resistor.

Thanks a lot,
mastertheknife.

[Th3_uN1Qu3]

Re: Samsung SyncMaster 226BW

Thank you PlainBill,
I just feel like trying my best to get it to work, before buying another board for $30 on ebay.
I believe the source of all problems was my flux. During soldering one of the capacitors,i accidently spilled too much flux.

Maybe you have the wrong kind of flux? I always use too much... never been a problem.

[mastertheknife]

Re: Samsung SyncMaster 226BW

Hi,

I probably didn't clean it well after spilling too much of it.
I cleaned the board by scrubbing it with an old soft toothbrush (works good actually) and then dried it but the 1-2 seconds to black problem still happens, so its probably something else now.

I monitored the ON\OFF pin coming from the signal board (pin 9) and enters the inverter IC at pin3 (after going through many resistors and transistors).
I was unable to monitor that pin near the IC because of limited access and the pins are so close together and i might short something out so i monitored the ON\OFF pin as it enters the board from the signal board.

Bad power supply board:
Monitor off = 0.0V
Monitor on\backlight on = 3.94V
Monitor on\backlight off = 3.94V
During pressing the Source button to turn on the backlight (for 1 second) i've seen the voltage drop to about 2.0V for less than a second.

Good power supply board:
Monitor off = 0.0V
Monitor on\backlight on = 3.93V
(Unable to monitor with backlight off because this board works)


Awaiting your ideas
Thanks,
mastertheknife.

[Th3_uN1Qu3]

Re: Samsung SyncMaster 226BW

I monitored the ON\OFF pin coming from the signal board (pin 9) and enters the inverter IC at pin3 (after going through many resistors and transistors).
I was unable to monitor that pin near the IC because of limited access and the pins are so close together and i might short something out so i monitored the ON\OFF pin as it enters the board from the signal board.

Bad power supply board:
Monitor off = 0.0V
Monitor on\backlight on = 3.94V
Monitor on\backlight off = 3.94V
During pressing the Source button to turn on the backlight (for 1 second) i've seen the voltage drop to about 2.0V for less than a second.

You know, you can always solder a thin wire to wherever you need and clip that for probing. Anyway your description shows an inverter problem, the logic board is fine (which we already knew since another power supply works). First thing, resolder the inverter transformers.

If it still doesn't work check the inverter IC for any protection that could be operating, post a link to the datasheet if you find it and don't understand it.

[mastertheknife]

Re: Samsung SyncMaster 226BW

You know, you can always solder a thin wire to wherever you need and clip that for probing. Anyway your description shows an inverter problem, the logic board is fine (which we already knew since another power supply works). First thing, resolder the inverter transformers.

If it still doesn't work check the inverter IC for any protection that could be operating, post a link to the datasheet if you find it and don't understand it.

I traced the pin's way and measured the resistance gained on the way on both boards and it seems unlikely to be the problem, its probably the inverter controller shutting down for some reason.
The chip is OZ964GN and the datasheet is here:
http://www.alldatasheet.com/datashee...2/OZ964GN.html

I resolded the inverter transformers, no luck.

As far as i understand the datasheet, there is an overvoltage protection but im not sure yet how this all works.

Thanks,
mastertheknife.

[Th3_uN1Qu3]

Re: Samsung SyncMaster 226BW

Okay this looks a lot like what i have on my NEC. The chip has three protections which go as follows:

• Overvoltage (pin 2). If this goes over 2 volts the inverter shuts down.
• Open lamp protection (pin 10). If this goes over 2.5 volts the inverter shuts down.
• Current feedback (pin 9), for protection against aged/shorted CCFLs. No clear description given in datasheet. Check against working unit, measure voltage across the resistor that goes from ground to the 51k resistor (R15 in the datasheet schematic). On mine it sits around 0.74v.

[jetadm123]

Re: Samsung SyncMaster 226BW

Yes, you've done a great job so far and I commend you on your hard work. After you perform the checks that Th3_uN1Qu3 suggested and if you find no problems, try checking the resistance of each secondary for each inverter. There should be no more than a 3% difference between the two.

[Th3_uN1Qu3]

Re: Samsung SyncMaster 226BW

Just for the sake of completeness - in practice that resistor mentioned as 474 on the datasheet isn't going to be in one piece because you have two sets of CCFLs. Just locate the 51k resistor, and find which end has a resistance of less than 1kOhm to ground. Then measure voltage from that end to ground and see what you get.

If all voltages are in check the problem is with the transformers. In my case it was bad soldering but you covered that already so one of them might be fried. Like jetadm123 said, if there's more than a 3% difference one of them is bad. On my NEC one was 1010 ohms IIRC, the other was 990-something. One more thing - it could also be a problem with the driver circuit. The 12v rail that the inverter feeds off of, is NOT monitored anywhere.

[mastertheknife]

Re: Samsung SyncMaster 226BW

Hi,

I will try that right away.
So far:
Open lamp protection - not likely, the lamps work with the other board.
Overvoltage Protection - likely, i just measured the resistance between pin5 (VDDA - "Supply Voltage") and +13VDC.
Good board = 6.0 Kohms
Bad board = 4.3 Kohms

This seems to be because of a resistor on pin5 (VDDA) just before it enters the IC.

Thanks again,
mastertheknife.

[Th3_uN1Qu3]

Re: Samsung SyncMaster 226BW

Maybe you understood this wrong. We will need the voltages on those pins, ie solder wires to each point for easy access and probe with the monitor ON and your meter on the 20 volts scale. The black lead of the meter will be always connected to ground. The most accessible ground is usually the green wire that goes from the 3 prong socket to the case. Label the wires after soldering or do like me and use only one wire. Solder, probe, unplug monitor, solder to next point.

And yes i understand that the CCFLs are known good - the protection could be kicking in because of another bad part.

[mastertheknife]

Re: Samsung SyncMaster 226BW

Hi Th3_uN1Qu3,

I suppose you refer to a resistor from pin9 (feedback control). There is a resistor next to it but its not 51kohms but rather 56kohms. Its other side is connected to ground (0 ohms). To check the voltage on the ground side of the resistor or on the pin side?

Also, i measured VDDA (Supply voltage) and it jumps between 4.6V to 5.0V which seems to be OK according to the datasheet.

EDIT: I just re-read one of your previous posts. In the meanwhile, i will solder wires to pin2 (overvoltage feedback) and pin10 (open lamp protection)

Thank you,
mastertheknife.

[Th3_uN1Qu3]

Re: Samsung SyncMaster 226BW

Maybe they changed it a little - all i can tell you is follow the datasheet. In your case it's best to just measure the voltage between pin9 and ground and compare to the other working supply. But before that, what do pin2 and pin10 measure?