Problems with Samsung 740N monitors

[Chungalin]

Re: Problems with Samsung 740N monitors

I got one of these for repair. No backlight. Image OK.

As expected, 3 bloated CapXon 820uF/25V (C111, C112, C301) and open 3A fuse (F301). Replaced everything and that's all.

[Behemot]

Re: Problems with Samsung 740N monitors

Test transformers and tubes as well.

[Venomus28]

Re: Problems with Samsung 740N monitors

Hello forum
I am a new member and i thought to post on this thread since i hope to help other people as it helped me.
I have two SyncMaster 940T monitors with the stand by light on and no image.
I found 3 bulged capacitors, which i am going to buy and replace tomorrow.
Thinking to get the 3A pico fuse too
I will keep you posted if that resolves my problem and if not id be very thankful if veteran members on this forum could help me getting further.

[bidomo]

Re: Problems with Samsung 740N monitors

Hey everyone!

This thread seems a little cold, so let's hope someone still reads this so I can get some help...

Well, in my case (740N), the fuse was blown, the capacitors are 1000uf 25v, I don't know if someone else replaced them and missed the fuse, the caps look fine (don't know how to identify the brand but will look into it).

I replaced the fuse with a 4A 250v glass tube, , the monitor seems to work fine (I can test it after I get some sleep and go buy a VGA cable afterwards), the "check the signal cable" is there, it will take some time till I get the right fuses, but there seems like some people think it is ok to use this kind of fuse, when others don't.

Is there a way to check if the inverter drivers are OK? I don't know much about electronics, but I'm willing to learn a little.

[Th3_uN1Qu3]

Re: Problems with Samsung 740N monitors

If you get the "check signal cable" screen then the inverter is OK. Sure you can check the MOSFET drivers, just use the diode check on your multimeter and measure between gate and drain, gate and source, drain and source. Measurements on the gate should check OPEN (OL or 1 on the left side), measurement between drain and source should show open one way and a diode drop the other.

That is with the part out of circuit, in-circuit gate to source will more than likely show a diode drop because there will be another transistor driving it. Simplified version is this: Open or diode drop is OK, short (zero) or low voltage drops (under 100mV) mean there is a fault in the transistor.

[Venomus28]

Re: Problems with Samsung 740N monitors

Hello forum i am back
Ive replaced the 3 bulged caps with new ones with exact same value as the old ones
Now the pico fuse i couldent get a same as old one green one but ive got a 3A smd fuse
Can i use the smd one or i should keep looking for a "green" one ?

[Behemot]

Re: Problems with Samsung 740N monitors

You can use any pico fuse you can find. Usually with these THT ones there is enough room to even use glass pico fuse.

[Venomus28]

Re: Problems with Samsung 740N monitors

Up the new one
Bottom the old one

[Behemot]

Re: Problems with Samsung 740N monitors

If you can manage to solder it there…

[bidomo]

Re: Problems with Samsung 740N monitors

If you can manage to solder it there…

The back side of the board seems safe to place it being SMD

[Venomus28]

Re: Problems with Samsung 740N monitors

Yes, i did that, the screen turned on for one second then, dark again lol
I bridged the fuse with a wire and now the stand by light pulses on and off ?
Ideas ?

[Th3_uN1Qu3]

Re: Problems with Samsung 740N monitors

You have shorted mosfets in the inverter. See my post above on how to check them.

[Venomus28]

Re: Problems with Samsung 740N monitors

Send me the link please

[Venomus28]

Re: Problems with Samsung 740N monitors

So on one monitor i had three bulged capacitors and a blown fuse, can anyone tell me what should i check to know why the fuse blow ?
And on the other one as Th3 uNiQu3 member suggested i have three bulged capacitors, a blown fuse and both mosfets shorted
(The fuse are now both replaced with 3A SDM)

[dinesh111]

Re: Problems with Samsung 740N monitors

thanks................................................

[jondoe]

Re: Problems with Samsung 740N monitors

Thank you for everyone's input into this thread, I have an ip-35135b from an IBM Think Vantage monitor, which must be a rebadged Samsung.

I've changed the three large filter caps for some 1000uf Suntans and replaced the pico fuse, only for the fuse to blow about an hour or so later. On closer inspection of the two AF4502C, one of them is testing for continuity from pin 3 to pins 5, 6, 7 and 8. That doesn't seem right and isn't reflected by the other. Probing around that circuit I found the ZD201 appears to be faulty, I get 0.2 on a diode test, on a working board it was 0.7, so I suspect it's fried.

Does anyone know the package type/size of the ZD201? I'm not very familiar with surface mounts, but I'm happy to try and replace the mosfets and zener to see if comes back to life for more than a couple of hours

Thanks.

[Behemot]

Re: Problems with Samsung 740N monitors

Usually you can replace SMD diode with leaded one.

[jondoe]

Re: Problems with Samsung 740N monitors

Sounds reasonable, but I wondered as the one installed has three pins, and leaded only has the two legs, how would I solder that in?

[Behemot]

Re: Problems with Samsung 740N monitors

Have you identified it? Some of them SOT-23 just have single diode with one end connected to two of the pins. Some actually have two diodes in single package (series, parallel or anti-parallel).

[jondoe]

Re: Problems with Samsung 740N monitors

I haven't quite identified it. I gather it's a 7.5 Zener of some description, I'm rather a novice at this kind of thing. Attached is an image as best I can make of it.