Samsung ln40b540p8f flickering

[technicallyartistic]

Re: Samsung ln40b540p8f flickering

Crap. This is the part where I need an oscilloscope now, isn't it?

[budm]

Re: Samsung ln40b540p8f flickering

https://www.badcaps.net/forum/showth...ht=BN44-00264B

BTW, there no sign of over heat by the Inverter transformer, right?

[budm]

Re: Samsung ln40b540p8f flickering

Crap. This is the part where I need an oscilloscope now, isn't it?

You may be able to see the fluctuation on the ENABLE pin of the IC if we can get the spec sheet of the IC.

[technicallyartistic]

Re: Samsung ln40b540p8f flickering

Of course it's near impossible to read. It looks like BD9893F. Anything else it looked like I couldn't find a data sheet for.

Below that it looks like it says 909 H10

No burn marks or swelling caps anywhere I can see. I've looked the board over a few times now.

You will have to walk me through what the plan is because I only understood what you were referring to with the help of Google before. I've dabbled with Arduino some and some small electronics stuff but not really anything that's been this in depth just yet.

Thanks btw for all the help so far. If nothing else maybe I can at least narrow it down for somebody else to repair. If I have to do something like remove that IC, my hands aren't steady enough to solder that good yet.

[budm]

Re: Samsung ln40b540p8f flickering

BD9893, so you need to check DCV between pin 12 and GND PIN 14 to see if it is fluctuating up and down.
The hard part will be is that it is on the bottom side so you may have to solder some wires to the test point to be able to make the measurement while the board is running.

[f67bird]

Re: Samsung ln40b540p8f flickering

Have you looked around the board for bad solder joints?
I have worked on a few of these same power supplies, some have blown mosfets and other components... in this case we usually buy the repair kit from shopjimmy and install it.
With the situation you are describing, I would look for bad caps and bad solder joints before replacing any components.
Dying ccfl's are also a possibility.

[technicallyartistic]

Re: Samsung ln40b540p8f flickering

I don't see any bad solder joints off hand, but I don't know if my eye is discerning enough to be able to spot them either.
So I know how to test the mosfets. Is there an easy way to test if the caps are bad or under-powered without plugging it in?

[technicallyartistic]

Re: Samsung ln40b540p8f flickering

Ok. I soldered on a wire like you suggested. A long wire so hopefully that doesn't make a difference.

Turned it on with the energy saving setting set to off.

At first it was a steady 1.683 v.
After it was on a while and the other modes were flashing it was 1.678 v

On low energy saver setting it was fluctuating between roughly 1.480 and 1.657 v

On the high energy saver setting which has a higher rate of flashing it was fluctuating between 1.510 and 1.652v

[budm]

Re: Samsung ln40b540p8f flickering

Ok. I soldered on a wire like you suggested. A long wire so hopefully that doesn't make a difference.

Turned it on with the energy saving setting set to off.

At first it was a steady 1.683 v.
After it was on a while and the other modes were flashing it was 1.678 v

On low energy saver setting it was fluctuating between roughly 1.480 and 1.657 v

On the high energy saver setting which has a higher rate of flashing it was fluctuating between 1.510 and 1.652v

Hmm, not 100% sure but it looks like the problem ein ENA signal.
Can you get me the P/N of ICP802 (it is next to the white fuse F1801S)?
I wish I have the diagram for this BN44-00264B version to see how the ENA pin is used.

[technicallyartistic]

Re: Samsung ln40b540p8f flickering

So it looks like that's maybe a transistor.

KA
431AZ
J48

I think at least. It was hard to read at that angle being blocked.

[budm]

Re: Samsung ln40b540p8f flickering

So it looks like that's maybe a transistor.

KA
431AZ
J48

I think at least. It was hard to read at that angle being blocked.

Programmable Shunt Regulator KA431.

[technicallyartistic]

Re: Samsung ln40b540p8f flickering

So is that potentially the issue? Or do we need to check that now?

[budm]

Re: Samsung ln40b540p8f flickering

OK, try shorting out the two pins of the OPTOISOLATOR PCI804S as marked in the picture together then power it up to see if it stops the flickering.

[technicallyartistic]

Re: Samsung ln40b540p8f flickering

Well it's been on for about 3 hours now and no flashing on any of the energy settings, so so far so good.

What did shorting the optoisolator do? (other than short it.)

[budm]

Re: Samsung ln40b540p8f flickering

I had you bypassed the PFC Under Voltage protection circuit. You PFC Voltage is on a little low side and probably on the border line @383VDC, we need to get it up to about 390~400VDC range.
I was able to trace out the circuit, but now I need to trace out the resistor network that is used for the Feedback which set the PFC output Voltage, more likely will be those Mega Ohms resistors that are connected in series that have gone up in resistance. I will let you know which resistors to test.
When PFC Voltage is low, the circuit will have to supply more current to maintain the power so more heat is generated that is because the regulator will try to maintain output Voltage that feeds the load, at this point you should turn down the Backlights level to as low as you can for now until we get the PFC Voltage back up to where it should be.

[budm]

Re: Samsung ln40b540p8f flickering

BTW, I need the P/N of the PFC Controller IC ICP801, I need to verify if it is FAN7530 or not.

[technicallyartistic]

Re: Samsung ln40b540p8f flickering

So I'm like 90% sure it says Fan 7503. The 5 kinda looks like a 6 maybe from certain angles and the 0 I can barely make out, but it's probably that. Looks like it says EK something up top. maybe EKO. It's all super worn off and only shows up at certain angles with certain light.

Should I remove the pin I soldered to short the optoisolator pins or leave that for now?

[budm]

Re: Samsung ln40b540p8f flickering

So I'm like 90% sure it says Fan 7503. The 5 kinda looks like a 6 maybe from certain angles and the 0 I can barely make out, but it's probably that. Looks like it says EK something up top. maybe EKO. It's all super worn off and only shows up at certain angles with certain light.

Should I remove the pin I soldered to short the optoisolator pins or leave that for now?

To raise the PFC Voltage up, we need to add resistor between pin 1 and Primary GND as shown in the picture, you can start with 100K 1/4W first to see how high the DCV on the two legs of the main filter will go up to, for now you can leave the jumper on the OPTO.

[technicallyartistic]

Re: Samsung ln40b540p8f flickering

Just to make sure I'm following correctly, it's just one resistor in the area to the right. Nothing is going to the two ground pins you circled? Or are we adding a resistor to any one of the pins with the resistor icon to the ground?

[budm]

Re: Samsung ln40b540p8f flickering

Just to make sure I'm following correctly, it's just one resistor in the area to the right. Nothing is going to the two ground pins you circled? Or are we adding a resistor to any one of the pins with the resistor icon to the ground?

Just one resistor, one leg goes to pin 1 as shown, the other leg goes to the circle (Negative leg of the cap CP811) which is GND or any one of those GNDs, but I would make the leg as short as possible so use what I had drawn in. The resistor may not ending up to be 100K, but we want to start with that value first.