SyncMaster 931BW no power

[BrAvE_26]

Hi all!
I'm new to this forum and I want to say that it was a great help for me with couple of old LCD's, and all I had to do is to search!

Now to the topic, I followed the troubleshoot here with no luck
My power board is of a different model PWI1704SV rev1.3
I connected just the power board without anything else and got a 4.9-4.95V on the 5.1V pins, 0V on the 13V pin and also on all the other pins.
So the problem is with the power board and I thought to myself that it's a good thing and I can fix that
The electrolytic caps seemed to be OK but just in case I replaced all of them except the C101 100mf 450V and two 22mF 50V(didn't have any ),
but i checked their capacity(my cheep voltmeter has a capacitor tester up to 200mF) and got 18mF which is good.
Checked the voltage on the C101 and got 314V which is OK (I live in Israel and we got 230V)

I followed Bill's excellent instructions and got to the FSDM0565R Power Switch(different from the original post I followed),
I measured the voltage between the Vcc and GND(pins 2 and 3 from this datasheet) and it varies from ~11V to 14V constantly.
According to Bill I need to change the start-up cap which in my case is C104(I think), so I did but it didn't help
I also tried to replace the power switch with another one just like it which I salvaged from another Samsung board but I got the same readings...
So now I'm stuck...

I attached pictures of the board with some markings, hope you can help me

[selldoor]

Re: SyncMaster 931BW no power

Its a great write up but you dont actually say what the problem is.
Please can you start from plugging it in to the final fault stage and tell us what happens.
What does the power led do what does the screen do any sounds clicks, wheezes etc - have a working video source connected whilst doing this.

[BrAvE_26]

Re: SyncMaster 931BW no power

LOL sorry I thought the title says it all
I have no power what so ever, no flickering, no power led indication, no sounds just dead.
Didn't try to connect it to a video source.

[selldoor]

Re: SyncMaster 931BW no power

Did you at some point do the voltage tests on the power supply>main connector when it was all connected up?

[BrAvE_26]

Re: SyncMaster 931BW no power

Yep, got the same results with the new capacitors.
But I didn't try to connect it all up again after I replaced the DM0565 power switch

[selldoor]

Re: SyncMaster 931BW no power

Ok can you try with it all connected up and can you also post a well lit close up picture of the soldering on the DM0565.
It may also be a good idea to look at all the solder joints with a magnifying glass as some look a bit odd R181 in bottom left C202 the righthand side joint c30 right hand joint - maybe its just the pictures - only you can check.

[selldoor]

Re: SyncMaster 931BW no power

Also check you got all the caps the right way round and can you tell us what make/series you used.

[Rtech]

Re: SyncMaster 931BW no power

D282 and D283 at the top of the Board should be checked for short circuit,as these regularly give problems.

[BrAvE_26]

Re: SyncMaster 931BW no power

Got it, I'm going to check everything out and post back.

[BrAvE_26]

Re: SyncMaster 931BW no power

Checked the solder joints, seems OK.
Checked all the caps for the right position and make/series:
1000mF, 470mF, 330mF all are Nichicon make, series PET
As for the diodes, which numbered 202 and 203(sorry for the poor picture from before),
when I connect the black lead to the cathode and red to the anode I get a read of 167 Ohms but according to this I should get 1K +-25%
so I don't really know if it's OK or not....
Connected it all up and still nothing....

[selldoor]

Re: SyncMaster 931BW no power

when I connect the black lead to the cathode and red to the anode I get a read of 167 Ohms but according to this I should get 1K +-25%
so I don't really know if it's OK or not....
.

Ok that is only half the diode test what do you get when you reverse the leads. Are both diodes reading the same? If in doubt they will have to be tested off the board.

Nichicon caps are usually ok unless you bought them on ebay.

I am still not sure about the soldering on the power control it "looks" as though the joints could be touching?

[BrAvE_26]

Re: SyncMaster 931BW no power

Both diodes read the same 167, and when I reverse the leads I get 1770 on both diodes.
Checked the joints on the DM0565 for short circuit and they aren't touching....
What should I do now?

[selldoor]

Re: SyncMaster 931BW no power

Remove the two diodes and check off board - one way should be offscale - at the moment it looks like they are bad.

[BrAvE_26]

Re: SyncMaster 931BW no power

Removed the diodes, one way goes of scale the other is 170 on the both of them.

[selldoor]

Re: SyncMaster 931BW no power

Thats a pity looks like they are ok - we will have to think of something else

[retiredcaps]

Re: SyncMaster 931BW no power

The fluctuating voltage on the SMPS IC is either

a) bad SMPS IC
b) bad startup cap
c) something shorted and loading down the SMPS

Since you already replaced the SMPS IC and startup cap, the next step is to check all your diodes (including the zeners and ones mounted on any heatsinks) to see if any are shorted.

[BrAvE_26]

Re: SyncMaster 931BW no power

Checked all the diodes and zeners and what do you know.... the D201 the one with the heat-sink is shorted I think...
It's model is MBR10150CT and all the pin combinations short out(1-2,1-3,2-3)
so is this my little problem!?

[tom66]

Re: SyncMaster 931BW no power

It sounds like it. Usually you'll hear a slight ticking sound when this happens though...

[BrAvE_26]

Re: SyncMaster 931BW no power

I found an MBR10150CT on a broken board and it doesn't short out!!!
I'm going to try and replace mine and see if it works and post back!

YES YES YES!
It works!!!! THANK you all never could I have done it without your help!


PS.
I hear a very very faint high pitched sound from the power board, should I be concerned?

[retiredcaps]

Re: SyncMaster 931BW no power

I hear a very very faint high pitched sound from the power board, should I be concerned?

It could be the little caps that you did not change?