Samsung SyncMaster 740N powers on now, very dim screen

[Pentium4]

My buddy gave me this monitor for free, it wouldn't turn on. I opened it to find that all 3 CapXon's on the secondary were bulged. The rest of the caps are Samxon KM series, so I left all of those. After replacing the bulged caps, it powers on now but the only way to see the picture is to shine a flashlight on it. The brightness and contrast are set to the highest. Did the lamp go bad in it?

[retiredcaps]

Re: Samsung SyncMaster 740N powers on now, very dim screen

After replacing the bulged caps, it powers on now but the only way to see the picture is to shine a flashlight on it. The brightness and contrast are set to the highest. Did the lamp go bad in it?

If you get no backlight, not even a quick flicker, you could have one of the following:

1) open fuse in the inverter section of the board
2) shorted transistor in the inverter section of the board
3) main board not sending a backlight on signal (typically > 2V DC)

A bad lamp would likely cause "2 second to black".

[Pentium4]

Re: Samsung SyncMaster 740N powers on now, very dim screen

If you get no backlight, not even a quick flicker, you could have one of the following:

1) open fuse in the inverter section of the board
2) shorted transistor in the inverter section of the board
3) main board not sending a backlight on signal (typically > 2V DC)

A bad lamp would likely cause "2 second to black".

Do you think bad caps could have caused any of those symptoms or is it just cause they're shitty CapXon so they died anyways? haha

[retiredcaps]

Re: Samsung SyncMaster 740N powers on now, very dim screen

Do you think bad caps could have caused any of those symptoms or is it just cause they're shitty CapXon so they died anyways? haha

Possibly. Collateral damaged caused by bad caps is beyond my current level of understanding.

[retiredcaps]

Re: Samsung SyncMaster 740N powers on now, very dim screen

Possibly. Collateral damaged caused by bad caps is beyond my current level of understanding.

But not budm's. See this post as budm talk about bad caps and how other components suffer.

https://www.badcaps.net/forum/showthread.php?t=23098

[Pentium4]

Re: Samsung SyncMaster 740N powers on now, very dim screen

Okay I verified that the problem is somewhere on the power supply. Had another 740N that was only a month older and replaced each board one at a time. Once I had the power board swapped out, the screen lit up nice and bright. I will bring my multimeter to work tomorrow, what should be the first thing to check? I attached a picture below, I hope it is clear enough.

[Pentium4]

Re: Samsung SyncMaster 740N powers on now, very dim screen

Think these bad joints could be causing issues? The two adjacent ones are a 1000uF 10V cap and the third joint is one on an inductor

On a side note, is that a mistake of printing on the board?

[retiredcaps]

Re: Samsung SyncMaster 740N powers on now, very dim screen

I will bring my multimeter to work tomorrow, what should be the first thing to check?

Same as post #2.

[Pentium4]

Re: Samsung SyncMaster 740N powers on now, very dim screen

Same as post #2.

Sounds good Do those joints look problematic though?

[budm]

Re: Samsung SyncMaster 740N powers on now, very dim screen

Lets find out for sure if you are even getting the high voltage pulse from both transformer at the out put side.
Unplug all the lamps from the sockets on the board.
Solder a piece of solid wire to the base of the lamp, then just touch the pad of the high voltage transformer and turn on the monitor while holding the lamp in your hand (you have to hold the lamp otherwise the lamp will not light up since it needs your body stray capacitance to complete the circuit) you see the lamp lights up for seconds.

[retiredcaps]

Re: Samsung SyncMaster 740N powers on now, very dim screen

Sounds good Do those joints look problematic though?

Looks like there is left over flux? Other than that, I have seen way way worse joints.

[mochini78]

Re: Samsung SyncMaster 740N powers on now, very dim screen

this works for me after replacing the 3 bad bloated caps and the open pico fuse, now its running smoothly as normal...

thanks

[gautamlondon]

Re: Samsung SyncMaster 740N powers on now, very dim screen

can some body tell me where should i check this 2v dc

main board not sending a backlight on signal (typically > 2V DC)

i have samsung 740n lcd and its screen lights up for a second or two then light goes off but screen is still on. i think its the inverter not getting backlight signal on once after turning the screen on


pls help its urgent

[dan8139]

Re: Samsung SyncMaster 740N powers on now, very dim screen

can some body tell me where should i check this 2v dc

main board not sending a backlight on signal (typically > 2V DC)

i have samsung 740n lcd and its screen lights up for a second or two then light goes off but screen is still on. i think its the inverter not getting backlight signal on once after turning the screen on


pls help its urgent

I had one like that and it was bad caps. Samsung liked to use poor caps.