Samsung ln40b540p8f flickering

[technicallyartistic]

Re: Samsung ln40b540p8f flickering

Ok. So I've got that soldered on. Now plug it back in and check the DCV on the main filter cap?

[technicallyartistic]

Re: Samsung ln40b540p8f flickering

Ok, so testing the main filter cap it's about 437 dcv with the energy saver setting set to off and fluctuating between around 420 and 430 on the high energy saver settings.
There is a noticeable audible clicking coming from the back now too.

[budm]

Re: Samsung ln40b540p8f flickering

That is too high! Remove the resistor. Try 200K instead.
Can you also take the resistance reading between pin 1 and GND before installing the new resistor so I will know what they are using? We only need to increase the Voltage by about 3% or so.

[technicallyartistic]

Re: Samsung ln40b540p8f flickering

Without a resistor it's about 39k.

[budm]

Re: Samsung ln40b540p8f flickering

Without a resistor it's about 39k.

OK, so it matches the resistor value used in the BN44-00264C.
CORRECTION: OK, try 1M resistor.

[technicallyartistic]

Re: Samsung ln40b540p8f flickering

I put on a 470k resistor because the next size up I have is 560k .
On the high energy saver setting is between 409-410. With the energy saver setting to off it's about 406, but it's clicking which I think are the bulbs flickering because the image has a flicker to it with the resistor on. Which is probably what the clicking was last time.

[budm]

Re: Samsung ln40b540p8f flickering

I put on a 470k resistor because the next size up I have is 560k .
On the high energy saver setting is between 409-410. With the energy saver setting to off it's about 406, but it's clicking which I think are the bulbs flickering because the image has a flicker to it with the resistor on. Which is probably what the clicking was last time.

That is still on the high side, you can try 1M or put the 560K in series with 470K if you do not have 1M.
BTW, is the jumper still in place at the OPTO?

[technicallyartistic]

Re: Samsung ln40b540p8f flickering

Yup. Jumper is still in place. I will put in the 1M

[technicallyartistic]

Re: Samsung ln40b540p8f flickering

Well I am a damn idiot and forgot to unplug the power from the board before removing it this time. We'll see if I destroyed this or not. I saw sparks and smell burning.

[technicallyartistic]

Re: Samsung ln40b540p8f flickering

Phew. I cleaned off the burnt area and everything seems fine. Just a bit of arcing.

This time it was 394 on the high energy saver.
392 with the energy saver off. Still some noticeable flashing and the clicking noise kinda like a project shutter sound.

[budm]

Re: Samsung ln40b540p8f flickering

Phew. I cleaned off the burnt area and everything seems fine. Just a bit of arcing.

This time it was 394 on the high energy saver.
392 with the energy saver off. Still some noticeable flashing and the clicking noise kinda like a project shutter sound.

OK, that does not make sense that it is still flashing with the jumper in place to bypass the PFC Under Voltage protection.
What does it do then if you remove the jumper but keep the resistor in place? 394VDC is good.

[technicallyartistic]

Re: Samsung ln40b540p8f flickering

So it's worse without the jumper. Like a more sporadic flashing on and off. Like before but not at a constant rate. The screen seems much dimmer on the high energy setting as well.

With the jumper it's still noticeably flickering but more like shutter flicker on an old projector than the on and off strobe before.

So far it's been best with just the jumper on, but I'm guessing there's a reason that isn't good for something on the board.

[budm]

Re: Samsung ln40b540p8f flickering

At this point I would leave the jumper in place and remove the 1M resistor, and hoping some one will have the same working board and the diagram to see what the normal Voltages should be, keep the backlights level as low as you can at this point.

[technicallyartistic]

Re: Samsung ln40b540p8f flickering

Eh, we aren't using it until its working right again. I like the idea of fixing stuff when I can, but trouble shooting this kind of stuff is why over my head. If nobody else here has any ideas I might just look and see if I can track down another board.

[budm]

Re: Samsung ln40b540p8f flickering

The bad is that we do not have the diagram for the 'B' version, we do have one for the 'C' version but it is exactly the same. I believe the 'C' version should work, they mad 'A' version, the 'B' version to fix what ever the problem they have with the 'A' version, and now they are using 'C' version so there must be some kind of problem with 'B' version which I think it may be related to flickering problem.
BTW, the KA431 drives the OTPO, is turned on (and then it turns on the OPTO) when PFC is higher than low Voltage trip point, it is turned off when the PFC Voltage is too low, there are a bunch of resistors connected in series which is then connected to the PFC output Voltage, so it can be that the KA431 is unstable, you can try replacing it.
The jumper on the OPTO is to simulate the OPTO is always ON. I cannot only do so much tracing the circuit using pictures which is really time consuming.
There are also some other Samsung boards with the same symptom and Samsung just has the bulletin out to bypass the Under Voltage shut down to stop the backlights from flickering.

[technicallyartistic]

Re: Samsung ln40b540p8f flickering

Well that's actually really helpful because I didn't know what the differences between the boards were and wasn't 100% sure the others were compatible.

[budm]

Re: Samsung ln40b540p8f flickering

Well that's actually really helpful because I didn't know what the differences between the boards were and wasn't 100% sure the others were compatible.

If you go to shopjimmy and look up BN44-00264b, I think he gives the list of the compatible boards.

[budm]

Re: Samsung ln40b540p8f flickering

I looked at the KA431 (ICP802) last night, there is a small Lytic filter cap CP812, you can try replacing that cap (no added resistor (1M) installed and the jumper removed from the Opto).
You can also see a bunch of resistors connected in series to feed the KA431 for sensing the PFC Voltage level (RP831, 32, 33, 34, 37, 38, 35). If you can monitor the DCV between the two legs of the cap, that will help so if the Voltage is staedy but the backlights is still flicker, then it can either be the KA431 or the Opto is bad.