Samsung 26in LN26B360C5D no picture good sound

[budm]

Re: Samsung 26in LN26B360C5D no picture good sound

We already know that the problem is in this power supply-inverter board, right now you are not getting 390~400VDC on the main DC filter cap, which you have indicate the reading of 165vdc on that cap, but then you indicate the reading of 56V between the fuse and the ground which is impossible and I am trying to find out how you come about getting 56V reading, one end of the fuse is connected to the positive leg of the cap, the other end of the fuse is connected to the load as you can see in the diagram.
So let me repeat the question again, are you getting steady 165VDC on the main filter cap CP815? If you do, then the voltage reading between the fuse and the negAtive HAS TO BE 165VDC.
The PFC circuit will have to be repair but not until we find out why your are getting 56VDC between fuse and ground.

[DakotaH]

Re: Samsung 26in LN26B360C5D no picture good sound

im getting 168vdc right now after clipping them on with clips and letting it set for about 30 sec

[budm]

Re: Samsung 26in LN26B360C5D no picture good sound

One bad thing about working on this board is that the board will have to be mounted in place with the board's fingers still sitting into the lamp sockets, if the high voltage for the backlght lamps starts working, you will get big spark. I would find the ground point on the top side of the board which is connected to the negative leg of the CP815 main filter cap for you Black probe of your meter.
So right now the PFC is not working properly, but do we have 165V between the fuse and the ground (negative leg of the CP815) as shown in post 41?

[DakotaH]

Re: Samsung 26in LN26B360C5D no picture good sound

yes

[budm]

Re: Samsung 26in LN26B360C5D no picture good sound

Good, that will explain why the sound is OK and the standby power supply is working for you to be able to turn the TV on/off.
We just have to fix the PFC circuit next.
Next thing to do is to find out if that QP802S is OK, you will have to remove it to take the resistance reading, we are looking for resistance leakage between Source pin and the Drain pin.

[DakotaH]

Re: Samsung 26in LN26B360C5D no picture good sound

6.3

[DakotaH]

Re: Samsung 26in LN26B360C5D no picture good sound

sorry sent that to the wrong one
its 39.3

[budm]

Re: Samsung 26in LN26B360C5D no picture good sound

39.3 Ohms, K Ohms, Mega Ohms?

[DakotaH]

Re: Samsung 26in LN26B360C5D no picture good sound

hold on im grabbing my new tester 126.5 with ohm meter set to just 200

[budm]

Re: Samsung 26in LN26B360C5D no picture good sound

OK, it sound like it has leakage resistance. Do you have any power supply that can put out 6~12V, or 9V batteries, and LED or 6v or 12v lamp?

[juice981]

Re: Samsung 26in LN26B360C5D no picture good sound

Hi, I have the same tv with the same problem, good sound but no backlight. Thing is, my board is from shopjimmy and its supposed to be already tested and working. I also get 165v at fuse FM802S. Is there any way to check if voltage is going to backlights? Can I measure from a finger to ground? Also when checking QP802S do I need to desolder the transistor from the board and is it right that the source and drain are the outer pins?

[juice981]

Re: Samsung 26in LN26B360C5D no picture good sound

I was able to see the menu while shining a flashlight so I guess this is just a backlight issue. How do I troubleshoot first without having to dissassemble down to the backlights themselves? It sounds simple, somehow get voltage to backlights, just not sure how or which circuit. Are the ccfls grounded or do they have a return circuit?

[budm]

Re: Samsung 26in LN26B360C5D no picture good sound

Well, the voltage on that large cap should go up to around 400VDC when TV is tun on, measure at the two pins of the cap. If you are only getting 165VDC, it means the PFC i snot working. Are also getting the same resistance reading as in post 49?
You cannot directly measure the high voltage output of the inverter since the voltage can be as high as 2000V which will blow your meter.

[juice981]

Re: Samsung 26in LN26B360C5D no picture good sound

How do I remove QP802S? Will it just pull out? Two of the leads has more than just a straight lead. Attached a pic.

[budm]

Re: Samsung 26in LN26B360C5D no picture good sound

At this point, you can take the resistance as is without removing it, just want to see if it show low resistance or not. The reading will be the middle pad and the right pad as shown in your picture.

[juice981]

Re: Samsung 26in LN26B360C5D no picture good sound

I am measuring around 7.61 MegaOhms.

[budm]

Re: Samsung 26in LN26B360C5D no picture good sound

That is good, so DakotaH has bad MOSFET.
So do you get around 400VDC on that large DC filter cap?
What happen if you remove the cables from the main board to the power supply board, the backlights should come on.

[juice981]

Re: Samsung 26in LN26B360C5D no picture good sound

I still only get 175VDC on the large filter cap and no backlights turn on after disconnecting the cable from the main board.

[budm]

Re: Samsung 26in LN26B360C5D no picture good sound

The PFC is not working. You can try new PFC IC UP801S as shown in the diagram, but I would like to get the resistance and voltage readings on all the pins first, you will be using the negative leg of the large filter cap as the ground ref point.

[juice981]

Re: Samsung 26in LN26B360C5D no picture good sound

Pretty big spark, hope I didnt destroy anything. I checked previous readings and they are the same.
Here is the reading for UP 801S:
Pin 1 = .46VDC
Pin 2 = 1.3mVDC
Pin 3 = .27VDC
Pin 4 = 161VDC
Pin 5 = 0VDC
Pin 6 = .1mVDC
Pin 7 = 137VDC
Pin 8 = .679VDC
This may be due to a cheap multimeter but I only get these values with test leads reversed (red on ground). With black test lead on ground point most values are less than 1 milliVolt and not more than 3 milliVolts.
Here are resistance readings:
Pin 1 = 1.216KOhms
Pin 2 = 42.6KOhms
Pin 3 = Open
Pin 4 = 75.5KOhms
Pin 5 = 10.2KOhms
Pin 6 = 1.1Ohms
Pin 7 = 1.463MOhms
Pin 8 = 1.635KOhms