Samsung 920Nx

[killian6pk]

I recapped this monitor checked the power to the main cap which appears ok. I reassembled and hooked to computer and power. No Power LED and not picture. Took it back apart and started reading power at connecter to VGA board.

On Power Board Connector On VGA Board Connector
Pin 1 = 12.53v Pin 1 = 12.53v
Pin 2 = 12.53v Pin 2 = 12.53v
Pin 3 = -7.2mv Pin 3 = -7.1mv
Pin 4 = -7.2mv Pin 4 = -7.2mv
Pin 5 = -7.2mv Pin 5 = -7.2mv
Pin 6 = 5.09v Pin 6 = 5.09v
Pin 7 = 5.09v Pin 7 = 5.09v
Pin 8 = 2.8mv Pin 8 = 2.8mv
Pin 9 = Gnd. Pin 9 = Gnd.

Also checked two Regulators or Transistors both had IC labels on VGA board.

IC 600 4 Pins counting Tab IC602 2 Pins + Tab
Pin 1 = -7.1mv Pin 1 = -7.0mv
Pin 2 = 3.296v Tab = 1.798v
Pin 3 = 5.09v Pin 3 = 5.09v
Tab = 3.295v

Not sure where to go from here.

[retiredcaps]

Re: Samsung 920Nx

On Power Board Connector On VGA Board Connector
Pin 1 = 12.53v Pin 1 = 12.53v
Pin 2 = 12.53v Pin 2 = 12.53v
Pin 3 = -7.2mv Pin 3 = -7.1mv
Pin 4 = -7.2mv Pin 4 = -7.2mv
Pin 5 = -7.2mv Pin 5 = -7.2mv
Pin 6 = 5.09v Pin 6 = 5.09v
Pin 7 = 5.09v Pin 7 = 5.09v
Pin 8 = 2.8mv Pin 8 = 2.8mv
Pin 9 = Gnd. Pin 9 = Gnd.

One of the above pins should be on/off signal from the logic/main board. When you press the on/off switch it should go from 0.0 V to > 2.0 V DC. It could be pin 8?

[killian6pk]

Re: Samsung 920Nx

I forgot to check for that I will do that now.

[killian6pk]

Re: Samsung 920Nx

I checked, with the Power Board connected to AC, the VGA board connected to power board and button board connected to VGA board. I get a power light, but no 2v on any of the pins there is also a ticking sound coming from one of the inverter transformers. Every time it ticks the power LED blinks.

[Scenic]

Re: Samsung 920Nx

Did you replace the little startup cap (close to the right heatsink in the first pic) as well?
checked for solder bridges?
I see chemicon, a lone rubycon and a panasonic cap. What series are they?

Ticking sound usually means the PSU is trying to start up, but can't because there either is a short on the output somewhere, or the little startup cap is bad (usually dried up).
Could maybe also be caused by totally off-spec caps compared to the originals, but that's not very common (seeing that you didn't use general purpose caps.. at least they don't look like it)

edit: looking at the photo again.. the panasonic (above C611) looks strange.. the gold tone doesn't look right.. fake cap?

[killian6pk]

Re: Samsung 920Nx

Yes I changed the small cap you are referring to. All the caps were good series low ESR caps FC, KY, KZH and the Rubicon is YXF and one Nichicon HE on the small cap. I will check a little closer for solder bridges. I have a couple of dark resistors I wonder if one of them might be the problem.

[alexanna]

Re: Samsung 920Nx

I checked, with the Power Board connected to AC, the VGA board connected to power board and button board connected to VGA board. I get a power light, but no 2v on any of the pins there is also a ticking sound coming from one of the inverter transformers. Every time it ticks the power LED blinks.

When you here the ticking and see the power LED blinking, Are the 5 and 12 volts pins steady?

[killian6pk]

Re: Samsung 920Nx

I checked the 5.0v supplies and one dropped to 4.16v and the other would go to OF and then go back to 4.12v.

The two 12.0v pins actually were reading 13.56v today. Both of those pins went to 12.52 every time the light blinked. All pins would revert back to there normal voltages after dropping down.

What is this an indication of?


P.S. I am still stuck on my other monitor questions. Where you told me to take pictures of the TCon.and someone else would pick it up. This Thread. Dell E207WFPc

[killian6pk]

Re: Samsung 920Nx

Did you replace the little startup cap (close to the right heatsink in the first pic) as well?
checked for solder bridges?
I see chemicon, a lone rubycon and a panasonic cap. What series are they?

Ticking sound usually means the PSU is trying to start up, but can't because there either is a short on the output somewhere, or the little startup cap is bad (usually dried up).
Could maybe also be caused by totally off-spec caps compared to the originals, but that's not very common (seeing that you didn't use general purpose caps.. at least they don't look like it)

edit: looking at the photo again.. the panasonic (above C611) looks strange.. the gold tone doesn't look right.. fake cap?

You know I have bought a few caps off Ebay, that could be possible that it is a fake. I will replace it just to make sure. I have some UCC's in the same specs I think.

[killian6pk]

Re: Samsung 920Nx

I changed that cap that might have been counterfit. It sure looks like it might have been. When I put the monitor back together i got a couple of new symptoms. The power LED came on and works as far as I know at least it turns off and on. I still don't have any backlights, but if I put a flashlight on the screen I can see the backlights flashing on and off just for a very brief second. So what is that an indication of?

[PlainBill]

Re: Samsung 920Nx

I changed that cap that might have been counterfit. It sure looks like it might have been. When I put the monitor back together i got a couple of new symptoms. The power LED came on and works as far as I know at least it turns off and on. I still don't have any backlights, but if I put a flashlight on the screen I can see the backlights flashing on and off just for a very brief second. So what is that an indication of?

A problem in the backlight system - inverter or CCFLs, with a slightly better chance that it is the CCFLs.

PlainBill

[killian6pk]

Re: Samsung 920Nx

I will check the secondaries on the inverter transformers. If it is the backlights themselves, I have already had a monitor with this same LCD screen. It was almost impossible to get the backlights out without tearing up the TCon mylar ribbon connectors. The screen is made by Hannspree or HannsG (all the same company). I will try to test switching out a pair of backlights and see if that is the problem.

[killian6pk]

Re: Samsung 920Nx

I checked the CCFL's by switching out a known good set and they flashed just like the originals. Replaced the top and then the bottom pair.

So I checked the transformers. These have four pins on one side and two on the other.

T602
Pin 1-2 0.621ko
Pin 1-3 0.622ko
Pin 1-4 1.244ko
Pin 2-3 0.0ko
Pin 2-4 0.622ko
Pin 3-4 0.623ko

2 Pins 0.3ko

T603
Pin 1-2 0.626ko
Pin 1-3 0.626ko
Pin 1-4 1.256ko
Pin 2-3 0.3ohms
Pin 2-4 0.626ko
Pin 3-4 0.626ko

2 Pins 0.3ko

[alexanna]

Re: Samsung 920Nx

I changed that cap that might have been counterfit. It sure looks like it might have been. When I put the monitor back together i got a couple of new symptoms. The power LED came on and works as far as I know at least it turns off and on. I still don't have any back lights, but if I put a flashlight on the screen I can see the back lights flashing on and off just for a very brief second. So what is that an indication of?

After you replaced the suspected cap did the 5 and 12volt pins become steady?
You say the front PLED is working,Is it also flashing about the same rate as the back lights?

[killian6pk]

Re: Samsung 920Nx

Yes it is flashing at the same rate. After replacing the cap. The readings also cycled with the flashing.
In the post above on the transformer readings I did not put the model number of the transformer down. I don't know if it is important but this is it. TMP90199CT. I will try and find a DataSheet on it.

[killian6pk]

Re: Samsung 920Nx

No luck on the DataSheet. Not really sure what the significant letters and numbers are. Tried several variations.

[PlainBill]

Re: Samsung 920Nx

I checked the CCFL's by switching out a known good set and they flashed just like the originals. Replaced the top and then the bottom pair.

So I checked the transformers. These have four pins on one side and two on the other.

T602
Pin 1-2 0.621ko
Pin 1-3 0.622ko
Pin 1-4 1.244ko
Pin 2-3 0.0ko
Pin 2-4 0.622ko
Pin 3-4 0.623ko

2 Pins 0.3ko

T603
Pin 1-2 0.626ko
Pin 1-3 0.626ko
Pin 1-4 1.256ko
Pin 2-3 0.3ohms
Pin 2-4 0.626ko
Pin 3-4 0.626ko

2 Pins 0.3ko

Rationalizing these numbers, the secondary is 1-4 with pins 2 & 3 as the center tap. All secondaries match to within 1%; it is unlikely either transformer is bad.

PlainBill

[alexanna]

Re: Samsung 920Nx

Yes it is flashing at the same rate. After replacing the cap. The readings also cycled with the flashing.
In the post above on the transformer readings I did not put the model number of the transformer down. I don't know if it is important but this is it. TMP90199CT. I will try and find a DataSheet on it.

I am not very good at looking at a picture and identifying the primary and secondary pins. About the only thing we can check with an ohmmeter on an inverter transformer is for an open on the primary side and the secondary resistances to be within 3% of each other, and from what I can see both of those are good.
I think you may have a shorted MOSFET for the inverter.
You could try removing the round inverter fuse, you will lose back lights.
But dose the Power LED work properly?
Dose it indicate a good signal is present?
Can you turn on and off the monitor by pushing the power switch?

[killian6pk]

Re: Samsung 920Nx

I will pull that fuse a little later on this afternoon. Have to run out for a few hours. Should I also pull the inverter MOSFET and test it?

[killian6pk]

Re: Samsung 920Nx

Pulled the fuse in the inverter area. Put the monitor back together (all boards in, all connectors plugged in) backlights connected. PLED came on green and stayed on. It would turn off and on. No backlights present. When you asked if there was a good signal present I'm not quite sure what you mean. I had the monitor connected to the computer also.