Black screen Samsung syncmaster 203B

[mani300]

Hi !
I have a little problem with my lcd display since couple of weeks, my screen has become black suddenly, we can see anyway with a flashlight some icons when i push the button menu for example.

I think the problem is the power supply board (i've attached the service manual), i have already change the bad caps but the screen is still black. May be it's the inverter or somehting else, i'm not so good in electronics, i just read a lot of thread like this and watch video, so i will try to be clear with my answers, i'm sorry for my english but i'm a french guy...

so please help me

[1supertech]

Re: Black screen Samsung syncmaster 203B

Check fuse F301,and F101 cap job doesn't look that great caps are too tall looks sloppy

[mani300]

Re: Black screen Samsung syncmaster 203B

How can i check this fuse ? i have a multimeter but i don't know how use it
yes, i've bought caps in a electronic store who have only this type of caps and no shorter. So i have to twist them...
If the soldering is good, it's ok no ? it looks like crap i know but i doesn't have a choice

[Agent24]

Re: Black screen Samsung syncmaster 203B

It's acceptable, but not optimal. Ideally you should get capacitors the right size. As long as nothing is shorting out or liable to short out, it's OK.

The bigger potential issue is that the lack of choice in capacitors means you may have a series which is not suitable for the circuit. This is unlikely to cause complete operation failure, though.

Likely the old, failed capacitors helped kill something else, you've solved the capacitor problem, now you have to find out what else went wrong because of them.


We need more info. You say you get a black screen, but do you get anything else? Does the power LED come on etc?

[mani300]

Re: Black screen Samsung syncmaster 203B

The new caps have the same specification that the old one, it's just the size is different.

When i turn on the screen, the power led is on (color blue, no flicking) but the screen is black, so the neon (backlighting) doesn't work.

Please how can i check the fuse with a multimeter ?

[Agent24]

Re: Black screen Samsung syncmaster 203B

With the monitor powered OFF, set the multimeter to the lowest resistance scale, or the continuity test function.

Connect one probe on either side of the fuse, you should get continuity beep or very close to zero ohms (like 0.01 Ohms or such). A fuse is just a piece of wire with basically no resistance. But when it blows, it goes open circuit, so you get nothing.

If you are confused as to what reading you should see - touch your probes to each other and see what the reading is. You should get much the same if the fuse is good.

You may also wish to read this: https://learn.sparkfun.com/tutorials...e-a-multimeter

[mani300]

Re: Black screen Samsung syncmaster 203B

i have testing with the continuity test function:
the fuse F301 get a big score and increase until overload
the fuse F101 get a zero or very close to that.

When i measure with the ohm meter the fuses outside the circuit:
F301 => nothing at all
F101 => (range 200 ohms) => 00.5

do you think that the problem will be solve by changing this 2 fuses ?

[Agent24]

Re: Black screen Samsung syncmaster 203B

It sounds like F101 is OK and F301 is blown.

This makes sense - F101 is the Mains fuse for the 240VAC and you do have power to the rest of the circuitry, while F301 is likely for the inverter circuitry, hence why you have no backlight.

Quite possible you have something shorted in the inverter section.

Unfortunately the service manual doesn't show the PSU schematic, only the mainboard, we can try to find another manual, but in the meantime:

Check for shorts to ground from both sides of the F301, you may get a low ohms reading on one side. If you do, probably there is a short somewhere in the inverter. If you don't, check anyway the two 8-Pin MOSFETs that drive the transformers, possibly one or both will be shorted.

Also if you can get a nice clear photo of the underside of the PSU that will help, as well as part numbers of those MOSFETs if you aren't sure how to check them.

[mani300]

Re: Black screen Samsung syncmaster 203B

I found this http://archive.espec.ws/files/sem2005.pdf and this for the mosfet http://www.aosmd.com/res/data_sheets/AOP610.pdf

if it can help, and 2 pictures of the inverter part.

[Agent24]

Re: Black screen Samsung syncmaster 203B

I would start with checking with diode test or resistance test across the power rails of the inverter (that is, across C316 - just after the fuse) If you get a low ohms reading, something is shorted and should be further investigated.

Of course you don't have to do this, but you will waste fuses if there is something wrong and you don't check.

I would check across those two MLCC ceramic SMD capacitors next to C316, the MOSFETs (check between the D1\S1 pins and D2\S2 pins, you should get only the body diode voltage drop when forward biased) You could also check between the Gate pins and other pins, there should be no connection at all.

[mani300]

Re: Black screen Samsung syncmaster 203B

Can you show me on the pictures of the circuit where exactly i got to check please?
for example, where is "across the c316" ? you know what i'm sayin' ?

and i don't understand all of your sentences like "you should get only the body diode voltage drop when forward biased" i'm sorry but its difficult for me, i know very few things in electronic, and added english it's even more harder


than you for all anyway

[Agent24]

Re: Black screen Samsung syncmaster 203B

OK, no worries, I will try to explain... When I say 'measure across', I mean to put the probes of your multimeter 'across' the leads of the component - one probe on each leg.

Typically this is said when talking about a component with two leads\legs: "measure across the component" - OR talking about two points in a circuit "measure across the voltage rail" (Hope that makes more sense??) - I've never really had to explain this so I don't really know the best way to say it!

In any case: See the picture I've attached that shows where to put the probes for the first test (Set to low ohms or continuity test). Hopefully this will explain better what I mean by 'across C316'

[mani300]

Re: Black screen Samsung syncmaster 203B

ok ok, thank you for the pictures, it help me a lot.
All is good then, so do you think that only the fuse F301 ? i will receive it soon anyway, i keep you posted.
Thanks

[Agent24]

Re: Black screen Samsung syncmaster 203B

I can't say with certainty that the inverter is OK, just that there is no short across its power rails. I think you should at least check the MOSFETs as well. (I will post a picture of where to check these too if you need)

[mani300]

Re: Black screen Samsung syncmaster 203B

I try to check the mofset thanks to your indications and the pdf document but i'm not sure, so yes if it not bother you i would like a picture
thanks !

[Agent24]

Re: Black screen Samsung syncmaster 203B

OK I have a list of 6 photos to test the MOSFETs. Use diode check mode, probe each pair of pins, and swap probes around so you check each pair in both directions. Do this for both MOSFETs.

You can also check the driver IC, ceramic capacitors, and transformers following the other photos. You shouldn't need to test both ways for these tests. Do the transformers with resistance test.

Write down the results and post them here. Hopefully it is easy to follow.

[mani300]

Re: Black screen Samsung syncmaster 203B

Thank you for all this pictures very understandable, so here's the results:

test1: overload; 636 (one direction; opposed direction)
test2: overload; 1601
test3: overload; 815
test4: 193; overload
test5: 1154 (not so sure my be overload too, various measures); overload
test6: 783; overload
for the other mosfets i've exactly the same results

test7: 673

test8: 630 (for the both capacitors)

test9: 1ohms may be less (0.8)
test 10: 1350ohms (red arrow) 1360ohms(blue arrow)

[Agent24]

Re: Black screen Samsung syncmaster 203B

Well it does not appear that any of those parts are shorted so that is good. I think you can try a new fuse and see what happens.

With regard to the transformer primaries, they are normally quite low ohms so that is OK.

[mani300]

Re: Black screen Samsung syncmaster 203B

Yessss it's perfect ! my screen work !
Thank you, thank you so much man, I appreciated all the things you've done for me.
And when i ordered the fuse, i order capacitors too with the right dimension, so i replaced them all, i should have take a picture, it's clean now

Thanks again, see you...

[Agent24]

Re: Black screen Samsung syncmaster 203B

Great!