Problems with Samsung 740N monitors

[Harvey]

Re: Problems with Samsung 740N monitors

Anyone know if the 720N uses the same, or similar, PSU?

[Soulace1970]

Re: Problems with Samsung 740N monitors

hi where is the 3A pico fuse found?

Alex

[EGuevarae]

Re: Problems with Samsung 740N monitors

This was ever resolved?
I have a 940T with the same PSU. Power led brights in a beautiful blue color, but no image or backlight. Also, I can't get V readings on the three bloated caps on the pic. I have replaced ALL the caps in the board (except the little one on the inverter side. As soon as I get image, I'll mess with that.

[Bobdee]

Re: Problems with Samsung 740N monitors

hi where is the 3A pico fuse found?

Alex

Hello alex,
I have not got a board with me, but from what I can see , there is a red fuse behind A/C connector,cylindrical in shape,but the one you may be after is possibly alongside of the big filter cap that is laying on ita side, its black and look like a diode or inductor,as I said I cant see properly from pictures,just check it out.
bob

[EGuevarae]

Re: Problems with Samsung 740N monitors

hi where is the 3A pico fuse found?

Alex

It is located under all that white stuff, at the side of a resistor, just at the side of the offending 820uf 25v caps.

[EGuevarae]

Re: Problems with Samsung 740N monitors

This was ever resolved?
I have a 940T with the same PSU. Power led brights in a beautiful blue color, but no image or backlight. Also, I can't get V readings on the three bloated caps on the pic. I have replaced ALL the caps in the board (except the little one on the inverter side. As soon as I get image, I'll mess with that.

Problem solved. While changin the fuse, checked the resistor at its side.
Resistor under the white stuff was badly/cold soldered.
Removed solder, resoldered, and now power flows in all the board.

And for the V readings, one of the jumpers was also badly soldered. I reflowed the solder on it, and problem solved. Too bad that after the LCD came to life it has a green line (like 2~3 pixels wide) across the right side.It has been narrowed down to the LCD Panel itself, as I have another unit and the problem moves if I exchange the lcd panels...too bad, excellent image and no damage to the screen ...

[gveranda]

Re: Problems with Samsung 740N monitors

This was ever resolved?
I have a 940T with the same PSU. Power led brights in a beautiful blue color, but no image or backlight. Also, I can't get V readings on the three bloated caps on the pic. I have replaced ALL the caps in the board (except the little one on the inverter side. As soon as I get image, I'll mess with that.

I Have a lcd with the same power board but it doesn't power at all I checked the voltages every where that i can see no readings at all even this big 1000uf 450v cap doesn't get any volt.can anyone here please help me to figure out anything thank you.really sorry if i pooped up the question in wrong location.

[Bobdee]

Re: Problems with Samsung 740N monitors

If you dont get green LED light up, check that red cyndrical fuse behind A/C connector, also fuse in power point plug.and the bridge rectifier

bob

[gveranda]

Re: Problems with Samsung 740N monitors

If you dont get green LED light up, check that red cyndrical fuse behind A/C connector, also fuse in power point plug.and the bridge rectifier

bob

Thanks for the reply bob,red fuse was blown as youve said and i replace that but it keeps happening again.any other ideas?sorry my knowledge it very limited thanks

[PlainBill]

Re: Problems with Samsung 740N monitors

Thanks for the reply bob,red fuse was blown as youve said and i replace that but it keeps happening again.any other ideas?sorry my knowledge it very limited thanks

If the fuse keeps blowing something is drawing too much current. Possible suspects are (in order) the switching transistor (on the large heatsink near the top of the large cap), the bridge rectifier (black rectangle near the bottom of the large cap), and the large cap itself. Use and ohmmeter and check each one out.

PlainBill

[gveranda]

Re: Problems with Samsung 740N monitors

If the fuse keeps blowing something is drawing too much current. Possible suspects are (in order) the switching transistor (on the large heatsink near the top of the large cap), the bridge rectifier (black rectangle near the bottom of the large cap), and the large cap itself. Use and ohmmeter and check each one out.

PlainBill

Thanks PlainBIll Just checked the board carefully and found that green colour part in between cylindrical fuse and blue capacitor has burnt(just below the yellow cubic) I really appreciate if someone can name them for me and get the value of that green thing looks like a resistor to me.Thank you guys.

[EGuevarae]

Re: Problems with Samsung 740N monitors

Thanks PlainBIll Just checked the board carefully and found that green colour part in between cylindrical fuse and blue capacitor has burnt(just below the yellow cubic) I really appreciate if someone can name them for me and get the value of that green thing looks like a resistor to me.Thank you guys.

Post a pic of your board , of the area with the suspected bad component.

[Bobdee]

Re: Problems with Samsung 740N monitors

tell us the letters/numbers on the board, probaby a thermistor, and any markings on it,
post pictures of your board if you can

[EGuevarae]

Re: Problems with Samsung 740N monitors

tell us the letters/numbers on the board, probaby a thermistor, and any markings on it,

Yep. If you can't post a pic, the marking on the silkscreen can help. I should have suggested that before.
Thanks, Bob.

[Bobdee]

Re: Problems with Samsung 740N monitors

sorry Eduardo,I did not know you posted on it,I was typing my reply while you posted ,I take ages to type anything

[EGuevarae]

Re: Problems with Samsung 740N monitors

sorry Eduardo,I did not know you posted on it,I was typing my reply while you posted ,I take ages to type anything

That is what makes this forum great : we complement each other. And it is nice to know that I'm not alone typing at 3:00AM too

[Bobdee]

Re: Problems with Samsung 740N monitors

It was easier for me, 11.00 AM here, but Im a Night Owl as well

[EGuevarae]

Re: Problems with Samsung 740N monitors

It was easier for me, 11.00 AM here, but Im a Night Owl as well

I forgot you are at the other side of the Atlantic. Now It is official : I am the only member browsing at 3:00am

[Bobdee]

Re: Problems with Samsung 740N monitors

yep , agreed

[mladen82]

Re: Problems with Samsung 740N monitors

I have repair many these boards from 740N too. Always three 820uF/25V CapXon GL 105 caps and one fuse 3A (axial green) after them. They are all on +13V power line which supplies inverter board.
In primary side there is an Fairchild smps pwm controller FSDM0565R.
Always too, on solder side of pcb, we can see that power copper lines +13V have some more yellow color than rest of board (that is green) and conlusion is that there was some over current flow.

Caps are bad quality for sure but there may be also some overvoltage on secondary side caused by iregular state of whole smps, even overvoltage from power line 220-240V.

Discovering right causes can be painful and ready for academic discuss.

Best way is to test new board with over voltage, high ambient temperature, open and short output circuits etc.

Caps and fuse aren't cheap and can't be problem, but when main A/D board or even lcd panel is dead also (on some other models) it can be a problem to judge whole case, as i have some.
https://www.badcaps.net/forum/showth...6020#post66020