Samsung Syncmaster 713N

[PlainBill]

Re: Samsung Syncmaster 713N

If you need better pictures , let me know.

Thank you!

They gave me all the information I needed, and a little bit more. First, the troubleshooting steps.

On the picture of the bottom I've circled four transistors in yellow. They are in pairs and are prone to fail when there is a problem with the Royer oscillator circuit. I've numbered the pins of one pair. Test by setting the DMM to the 200 ohms range and measuring resistances 1-2, 1-3, 2-3. Odds are both members of a pair will be shorted, the other pair will be fine. IF one pair is shorted you can stop looking for the cause of the 'no CCFLs' problem and move on to locating the cause.

If the transistors were not shorted, there are two diodes circled in yellow. Check them for shorts. If they are fine, check the FETs (8 pin ICs) for shorts.

I've circled four leads in red. Those on the right look like they may have been cracked. A bad solder joint will cause the transistor failure. Also, I neglected to do the same for the leads on the transformers, although they look fine. It would be a good idea to resolder all of them.

Orange circle - Not a very good soldering job. Check that.

Top side of board.

Red circles - the caps circled in red can also cause the transistors to fail.

Orange circles - bad soldering technique. The caps should be pushed down to the board. And a question - what brand and series of caps did you use?

If the transistors are shorted, they are Rohm 2SC4672. Digikey has them as 2SC4672T100QCT-ND for about $.75 each. They are also available on eBay. If one is shorted, always replace both in the pair.

PlainBill

[Peter9DO]

Re: Samsung Syncmaster 713N

Note: Just because a cap is not bulging, does not mean that it's good. ESR levels can show otherwise... I would replace C13 and the cap next to it as well if you don't have an ESR tester. If you do, test them and you might find that the ESR is a little to high... As selldoor said I would be a little curious as to why there is that mess on the board near the C13 cap that has not been replaced.

[selldoor]

Re: Samsung Syncmaster 713N

Hi it would appear you have not replaced all the capacitors? there are still some
capxons in there? First step might be to replace them but probably not the big one.
What happened to C18 - looks a disaster both sides of the board I will try and find a pic of the back somewhere and see.
What make caps did you use as replacements? I am hoping you at least went for the same values.

[SmartVision]

Re: Samsung Syncmaster 713N

If you need better pictures , let me know.

Thank you!

[PlainBill]

Re: Samsung Syncmaster 713N

The fact that the CCFLs do not light when connected to the left side indicates a problem. I need sharp pictures of both top and bottom sides of the power supply / inverter.

PlainBill

[SmartVision]

Re: Samsung Syncmaster 713N

Ok I think I was wrong.

First I connected both lamps to connectors above power jack (picture 1) and nothing happens , no blinking of lamps but still I hear that "click" noise.

Then I connected both lamps to connectors above capacitors (picture 2) and lamps blink every 5 seconds , still that noise heard.

Very important , I think I was wrong about that niose , I think it is coming from big transformer in the middle.

Now it seems more difficult to find a real problem becouse maybe there is more problems , like this big transformer and this smaller above capacitors.

I don't have much luck

[PlainBill]

Re: Samsung Syncmaster 713N

Cap is not bulging , just bad picture quality.

I checked this tranformer and it is SPI 8TC00190.

If found in google this:
http://elektronik-service.com.pl/tow..._8tc00190.html

SPI 8TC00190 CCFL BACKLIGHT INVERTER TRANSFORMER SAMSUNG

So it looks like that they may cause the problems often.

Maybe, maybe not. Some Samsung models DO have a history of bad inverter transformers.

Have you tried hooking the CCFLs to only one set of outputs at a time and observing the results? If both sets of CCFLs will light when hooked to the other transformer but not the dark one the problem is the dark transformer.

PlainBill

[SmartVision]

Re: Samsung Syncmaster 713N

Cap is not bulging , just bad picture quality.

I checked this tranformer and it is SPI 8TC00190.

If found in google this:
http://elektronik-service.com.pl/tow..._8tc00190.html

SPI 8TC00190 CCFL BACKLIGHT INVERTER TRANSFORMER SAMSUNG

So it looks like that they may cause the problems often.

[PlainBill]

Re: Samsung Syncmaster 713N

Hi there.

Sorry for not answering after my last attendance at forum , I didn't have much free time to open monitor again, now I got some time and I opened monitor to check CCFL lamps.

First I want to answer you on your question about capacitors , new capacitors are Jamicon.

Today I was curious what happens with CCFL lamps and found this:

http://www.youtube.com/watch?v=OhQTc...ature=youtu.be

So lamps blink every 5 seconds and there is a "click" sound on board (see on picture , marked part if I'm right , also I think you can't hear that noise on video, maybe with some headphones)


So I think that is the problem or not ?

Thank you.

That transformer is suspiciously dark, that could be the problem. Also, there appears to be a bulging cap near the bottom.

PlainBill

[SmartVision]

Re: Samsung Syncmaster 713N

Hi there.

Sorry for not answering after my last attendance at forum , I didn't have much free time to open monitor again, now I got some time and I opened monitor to check CCFL lamps.

First I want to answer you on your question about capacitors , new capacitors are Jamicon.

Today I was curious what happens with CCFL lamps and found this:

http://www.youtube.com/watch?v=OhQTc...ature=youtu.be

So lamps blink every 5 seconds and there is a "click" sound on board (see on picture , marked part if I'm right , also I think you can't hear that noise on video, maybe with some headphones)


So I think that is the problem or not ?

Thank you.

[PlainBill]

Re: Samsung Syncmaster 713N

Hi again .

My friend has this monitor and it's not working well.

When it's plugged, green indicator is on , but display is black . It just blinks for a second (displaying Samsung configuration frame) after about 10 sec after turning monitor on.

We changed capacitors on its Power supply except of the biggest capacitor , but it didn't help.

Any suggestions are welcome , thanks .

The problem is known as 'Two seconds to black'. The usual causes are bad capacitors, bad (shorted or open) transformers, bad CCFLS or the wiring to the CCFLs, and a fault in the protection circuitry.

1. What brand and series of replacement caps did you use? Even new standard ESR caps have been known to cause this problem.

2. To check the inverter transformers, measure the resistance of the secondaries. The resistances should match to within 3%

3. Broken or aging CCFLs can cause the problem. A broken lead to a CCFL, or a break in the insulation on the leads will also cause the problem.

PlainBill

[SmartVision]

Hi again .

My friend has this monitor and it's not working well.

When it's plugged, green indicator is on , but display is black . It just blinks for a second (displaying Samsung configuration frame) after about 10 sec after turning monitor on.

We changed capacitors on its Power supply except of the biggest capacitor , but it didn't help.

Any suggestions are welcome , thanks .