Problems with Samsung 740N monitors

[PlainBill]

Re: Problems with Samsung 740N monitors

hello everybody!
I read this thread multiple times, even locked the tab in firefox so i can check it daily. It seems i`m having the exact same problem user "ethernet" has. Problem is he kind of gave up on trying (last post like 7 months ago) and my electronics knowledge is all but absent so i can`t answer questions and bring the same level of information like he did.
So: when i turn it on it sounds like it starts charging (like a camera flash, but not a linear pitch, more like an oscillating growing pitch) then the lamps flash (very short, like 100 ms) and i even see the image, then no sound for a short while after witch it cycles. Any help would be much appreciated
I can record the sound and search for some web host to upload it if you find it necessary.

I doubt a recording of the sound would help. Some of us wouldn't even be able to hear it! What test equipment do you have? I've reviewed ethernet's posts and there are two possible causes.

PlainBill

[sequille]

Re: Problems with Samsung 740N monitors

I have no testing equipment. I could ask people i know but what should i ask for? On the sound: I can pitch it down, that should make it audible for all ages.

[PlainBill]

Re: Problems with Samsung 740N monitors

I have no testing equipment. I could ask people i know but what should i ask for? On the sound: I can pitch it down, that should make it audible for all ages.

The sound indicates the transformer is overloaded. I suspect the problem lies in the feedback to the SMPS controller. The fault either lies on the output side (voltage reference or opto-isolator are most likely), or on the primary side (SMPS controller, optoisolator, feedback components).

There are three ways to repair this. The best way is to look up the application note covering the controller, identify the components used on this board, and measure the feedback voltages. Once the defective component is located, it can be replaced. The second approach is to 'shotgun' by replacing all components on both sides. Unfortunately, you don't have the equipment to troubleshoot, and obtaining the parts may be expensive. There is also the matter of the skills necessary to replace the components. That leaves the third option - obtain a good power supply / inverter board.

PlainBill

[tanozuke]

Re: Problems with Samsung 740N monitors

Please could some one help me. I have a question, how can i test a BIT3193 PWM Controller.

Heres is the link.



and also how to test a FSDM0565RB is an integrated Pulse Width Modulator (PWM) and Sense FET

Here is the link.

http://www.datasheetpro.com/181698_d...datasheet.html

Thank you.

[Ch1p4@ll]

Re: Problems with Samsung 740N monitors

Greeting... 1st iam newbie... i have this 740N too... i have changed "820uf 25v x3" (a little Leak, considered Broken) to "1000uf 25V x2" and "470uf 25V", the light was still off! so i Shortwired a fuse "3AE" Ok! the light has showed up... the problem is... there is a waving noise on the screen... what should i checked? plzzz help me.

[seemore]

Re: Problems with Samsung 740N monitors

I have 740N with strange problem. First when I switch ON, i get image and backlight. After 2 seconds the backlight is OFF, and the image is OK, i can see it if i use flashlight.
I can switch OFF/ON again and the backlight starts, but again only for 2 sec. I opened it, and saw the inverter board, but the caps looks OK. The fuse is OK.

What would u say? Do u think i have to start with changing 3 caps, or all the caps ? Do u think the problem is in the Lamp itself ? Or the BIT3193G PWM Controller?
It works for 2 sec ... than goes OFF.

[PlainBill]

Re: Problems with Samsung 740N monitors

I have 740N with strange problem. First when I switch ON, i get image and backlight. After 2 seconds the backlight is OFF, and the image is OK, i can see it if i use flashlight.
I can switch OFF/ON again and the backlight starts, but again only for 2 sec. I opened it, and saw the inverter board, but the caps looks OK. The fuse is OK.

What would u say? Do u think i have to start with changing 3 caps, or all the caps ? Do u think the problem is in the Lamp itself ? Or the BIT3193G PWM Controller?
It works for 2 sec ... than goes OFF.

It could be the caps, a lamp, or a bad transformer. For starters, resolder the inverter transformers. If that doesn't fix it, read this faq https://www.badcaps.net/forum/showthread.php?t=1868 Then take pictures and attach them to your next post.

PlainBill

[Oerg866]

Re: Problems with Samsung 740N monitors

Hello, ugh.

I got this very nice Samsung SyncMaster 940B for free from a friend who found it at his helectronics dumpster at work. So we tested it and it had no backlight.

I replaced the 3 caps by 3x470uF (Panasonic) and 1x 1000uF (Grand Sonic) 25V (that last one is borrowed from a C64, hehe) and the fuse I replaced with a very small wire.

Worked great for 3 hours, and then poof, the light is off, and then for a fraction of a second on again and repeats. I took the board out again and nothing looks broken, the caps are still working and the fuse wire isn't burnt.

Any help would be appreciated.

Cheers

[PlainBill]

Re: Problems with Samsung 740N monitors

Hello, ugh.

I got this very nice Samsung SyncMaster 940B for free from a friend who found it at his helectronics dumpster at work. So we tested it and it had no backlight.

I replaced the 3 caps by 3x470uF (Panasonic) and 1x 1000uF (Grand Sonic) 25V (that last one is borrowed from a C64, hehe) and the fuse I replaced with a very small wire.

Worked great for 3 hours, and then poof, the light is off, and then for a fraction of a second on again and repeats. I took the board out again and nothing looks broken, the caps are still working and the fuse wire isn't burnt.

Any help would be appreciated.

Cheers

Fuses blow for a reason. Almost always the reason is something is drawing too much current. In this case, the inverter. Possibilities include a shorted transformer or transistor. (Actually, I'd suspect a bad transformer caused excessive current draw. Since you shorted the fuse, the drive transistors shorted.

PlainBill

[sequille]

Re: Problems with Samsung 740N monitors

I bought a 4 lamp inverter, it has tree wires: red, black and yellow. Is there any way i can connect it to the monitor's power supply (and in what points) or should i use an external power supply for it?
I assume the yellow wire is for brightness control, the 2 lamp inverter i got for another monitor had no such wire. But on that one the inverter was "standalone", i just had to tap into the old one's connector. Here, if possible, i'd have to connect it directly to the board.

[PlainBill]

Re: Problems with Samsung 740N monitors

I bought a 4 lamp inverter, it has tree wires: red, black and yellow. Is there any way i can connect it to the monitor's power supply (and in what points) or should i use an external power supply for it?
I assume the yellow wire is for brightness control, the 2 lamp inverter i got for another monitor had no such wire. But on that one the inverter was "standalone", i just had to tap into the old one's connector. Here, if possible, i'd have to connect it directly to the board.

This leaves me with a dilemma. I consider my activity here as an opportunity to both assist and to educate. Some of life's most educational moments occur when you f***k up big time. Certainly starting a fire because you haphazardly modified your monitor would be a truly educational event.

There is another issue. I have a wealth of experience in many different fields. In rare moments I have been able to pull those experiences together to solve problems or pose possible solutions to a problem. NOTHING in my experience has prepared me to know how to hook an unknown inverter up to a monitor I have never seen. However, my experience does tell me this has all the earmarks of a very bad idea.

I suggest fixing the original inverter. Failing that, I suggest asking the supplier of your new inverter how to hook it up. And while you are discussing it with him, I suggest asking him if the warranty covers consequential damage.

PlainBill

[sequille]

Re: Problems with Samsung 740N monitors

well, i did manage to blow a transistor from an inverter i got for another monitor, and i did witness an electrical arc upon trying connect the CCFL to the inverter while it was powered, but no fire . I found the inverter on some Chinese site, it seems the yellow is for on/off. so even if i power it externally i still need to know what voltage is for the on/off pin, which i don't.
when i asked if you could help me solder it directly to the board i thought someone posted a diagram of the PSU here, but i re-read and couldn't find it again, it must have been another site. So for me it wasn't really asking to connect an unknown inverter to an unknown psu as you said, i had some other info in my head. I understand now that i had given too little info and it sounded like something someone shouldn't do.
Also, since the 3A fuse connects the inverter part to the psu part i thought that would be where the red wire goes and all i needed was a ground point (for the black) and a point for the yellow (which only now i know is just for on/off, not for brightness control).


I'm waiting for an answer from the supplier, i thought i'd post this in the meantime.

[seemore]

Re: Problems with Samsung 740N monitors

I have 740N with strange problem. First when I switch ON, i get image and backlight. After 2 seconds the backlight is OFF, and the image is OK, i can see it if i use flashlight.
I can switch OFF/ON again and the backlight starts, but again only for 2 sec. I opened it, and saw the inverter board, but the caps looks OK. The fuse is OK.

What would u say? Do u think i have to start with changing 3 caps, or all the caps ? Do u think the problem is in the Lamp itself ? Or the BIT3193G PWM Controller?
It works for 2 sec ... than goes OFF.

I've changed all the caps on the inverter, and re-soldered most of the other elements ... nothing happened.
I'm pretty sure the problem isn't in the lamp - i tested it with another inverter and it works fine.
So what to try next ? The fuse near the 3 caps is OK.

[PlainBill]

Re: Problems with Samsung 740N monitors

I've changed all the caps on the inverter, and re-soldered most of the other elements ... nothing happened.
I'm pretty sure the problem isn't in the lamp - i tested it with another inverter and it works fine.
So what to try next ? The fuse near the 3 caps is OK.

There are several options. Do you have other CCFLs that you can hook up to this inverter? If not, a picture of the back side of the power supply / inverter is the next step. You are going to have to make some resistance and voltage measurements.

PlainBill

[seemore]

Re: Problems with Samsung 740N monitors

There are several options. Do you have other CCFLs that you can hook up to this inverter? If not, a picture of the back side of the power supply / inverter is the next step. You are going to have to make some resistance and voltage measurements.

PlainBill

10x for replay.
I tested the inverter with another lamp - it starts, and after a second it turns off. It's the same like the original lamp.
I made a picture of the back side, but i don't think there is something unusual there - I've already re-soldered most of the elements.
So how can i test BIT3193 PWM Controller, like another user asked before ? I can try to change it without testing - it's under $10 i think, but i'm not very good with my solder, and it would not be easy to change it

[PlainBill]

Re: Problems with Samsung 740N monitors

10x for replay.
I tested the inverter with another lamp - it starts, and after a second it turns off. It's the same like the original lamp.
I made a picture of the back side, but i don't think there is something unusual there - I've already re-soldered most of the elements.
So how can i test BIT3193 PWM Controller, like another user asked before ? I can try to change it without testing - it's under $10 i think, but i'm not very good with my solder, and it would not be easy to change it

When you take your car in for repair, do you tell the mechanic how to fix it? While this isn't brain surgery, I sure hope you don't tell your doctor how to treat your ailments. On a positive note, the picture is quite good.

While it is possible the backlight controller is bad, it's rather unlikely. It is far more likely the problem is due to a transformer or a CCFL.

I've marked up the picture. There are several readings to take. Include them in your response.

1. With power OFF (monitor unplugged), measure the resistance from Output 1 to Output 2. Also measure the resistance from Output 3 to Output 4.

2. The following steps are done with power on. It is best if you have a helper who will cycle the power button (push it slowly twice) while you make each reading. They can also call 911 if you get careless and electrocute yourself. For this reason, the helper should be someone who does not stand to gain by your demise.

Set the meter to AC volts. Measure the voltage from V Sense 1, V Sense 2, I Ret 1, I Ret 2, I Ret 3, and I Ret 4 to Ground (lower left corner of the board) while the backlights are on.

PlainBill

[seemore]

Re: Problems with Samsung 740N monitors

Hello again,
The resistance from Output 1 to Output 2 and from Output 3 to Output 4 is 1.3 kOhm. Is that OK ?
The other measurements sound a little dangerous, and i'll ask someone else to make them, than i'll post the values

[PlainBill]

Re: Problems with Samsung 740N monitors

Hello again,
The resistance from Output 1 to Output 2 and from Output 3 to Output 4 is 1.3 kOhm. Is that OK ?
The other measurements sound a little dangerous, and i'll ask someone else to make them, than i'll post the values

1.3K is in the right range, but what are the exact numbers? A difference between the two transformers could indicate a problem.

PlainBill

[Hallucin]

Re: Problems with Samsung 740N monitors

I have 740N with strange problem. First when I switch ON, i get image and backlight. After 2 seconds the backlight is OFF, and the image is OK, i can see it if i use flashlight.

same to me...i changed all caps and nothing :S
check my
POST ,just in case if we have same problem.

[seemore]

Re: Problems with Samsung 740N monitors

1.3K is in the right range, but what are the exact numbers? A difference between the two transformers could indicate a problem.

PlainBill

1305 Ohms on the right transformer, and 1235 Ohms on the other one.