Samsung LN-S3251D

[PlainBill]

Re: Samsung LN-S3251D

Attached is a pic of the latest readings.
#1 and #4 are SC156615M 2.5 LDO Regulators. (scope set @ 1 and 1)
#2 (17-18 06161L) and #5 (17-25 06182L) are what I believe to be LDO Regulator's. (scope set @ 5 and 1)
#3 (78M08A G2 1B) is what I believe to be another type of regulator showing a steady 8V on the input and a very, very, very short wavy 8V (1V PtP) on the output. (scope set @ 5 and 1)
I am unable to locate any type of data-sheets on #2, 3, & 5.
AC or DC coupling seems to make little difference in the readings.
Next steps please....

#3 is a 78M08. It's a 'jellybean part - made by many different manufacturers. It should have a minimum of 2 volts difference between input and output. The tab is ground.
#2 should be a 1.8 volt regulator (perhaps the tab is the output?) and #5 would be the 2.5 volt version. I'm running into advanced senility at the moment and can't remember that package type....

Got It!! #2 is a AP1117K18L-13 or equivalent in a T0-263 package, #5 is aAP1117K25L-13 or equivalent. In each case, the tab is the output.

PlainBill

[PlainBill]

Re: Samsung LN-S3251D

I'd check the output voltage of #2 and #5, but they probably are clean.

I suspect the problem is the supply for #3. Something is holding it down into the drop-out region.

PlainBill

[Sam I Am]

Re: Samsung LN-S3251D

Output voltage of #2 is a clean 1.8V and #5 is a clean 2.4V.
#3 is a clean 8V in and a wavy 13.2V out (I guess I read it wrong yesterday).
What about #4.... since pin 5 is equaling pin 4.... should there be a difference like #1?
I'm confused but then again.......

[PlainBill]

Re: Samsung LN-S3251D

Output voltage of #2 is a clean 1.8V and #5 is a clean 2.4V.
#3 is a clean 8V in and a wavy 13.2V out (I guess I read it wrong yesterday).
What about #4.... since pin 5 is equaling pin 4.... should there be a difference like #1?
I'm confused but then again.......

I think you are reading #3 backwards. That particular part is available in several pin configurations. The common one is input on the left, ground is in the middle, output is on the right.

PlainBill

[Sam I Am]

Re: Samsung LN-S3251D

That is quite possible but at least there is difference in voltage between input /output today whereas yesterday I thought they were the same.
What about component #4 (SC1566), pin 4 & 5?

[el3ctroded]

Re: Samsung LN-S3251D

You don't need to worry with Pin 5, it's the voltage adjust pin: the pin used to set the output on the regulator. So long as pin 4 is clean, it's good.

Here's something to try to more carefully test each output:
1) Set oscilloscope to 200mv/div and set the coupling to AC, and the Time/div to 1sec.
2) on each regulator, watch the voltage output and while doing so adjust the tive/div through it's whole range. At each change, watch the scope for for large noise spikes and/or superimposed sine waves.

[Sam I Am]

Re: Samsung LN-S3251D

So.... are all of my voltages within spec and have I located all of the regulators on this board? If so, then should I just go ahead and locate a main board somewhere or is this one repairable?

[Sam I Am]

Re: Samsung LN-S3251D

Oops... didn't see the rest of your post.
Will scope it according to your recommendations and get back to you.

[el3ctroded]

Re: Samsung LN-S3251D

I don't see any other obvious regulators. That said, there's an area where none of your pictures shows. It's below where the Input/Output connectors are. I see the edges of some caps...

Have you checked the Tcon board for regulators? They would usually be in a smaller package than the ones on this board.

[Sam I Am]

Re: Samsung LN-S3251D

Outputs on all but #3 are clean. #3 is showing a .1V PtP signal.
Sheesh.... the components on the Tcon board are even smaller, might have to invest in a microscope.
If I'm not mistaken, Wizard felt the problem was somewhere on the main board.
Now what.....

[el3ctroded]

Re: Samsung LN-S3251D

#3 could maybe be the issue. 0.1v isn't bad, but.... Check the ESR of the caps around this regulator.

Yes, wizard did say that, but if we rule out all the regulators, it may be caused by a different issue.

Did you check that other area below the A/V connectors for regulators?

You shouldn't need a microscope, just a high power, clear, magnifying glass.

[el3ctroded]

Re: Samsung LN-S3251D

Is the 0.1V ptp signal random looking noise or oscillation?

[Sam I Am]

Re: Samsung LN-S3251D

Cool Beans showing up as a member now... must of hit the magic number or something.

AC coupled on #3 lower pin is oscillating like a mini sine wave and the ESR of the four caps on the pin side vary from .02 - .19. Also, no other regs exist near the A/V inputs.
Is this type of oscillation considered abnormal?

[PlainBill]

Re: Samsung LN-S3251D

Cool Beans showing up as a member now... must of hit the magic number or something.

AC coupled on #3 lower pin is oscillating like a mini sine wave and the ESR of the four caps on the pin side vary from .02 - .19. Also, no other regs exist near the A/V inputs.
Is this type of oscillation considered abnormal?

Those ESR numbers seem high. Suggestion: Compare the ESR readings you got with an equivalent low ESR part. As an example, with the equivalent Panasonic FC cap. If it's even close, replace the caps with FC or better yet, Panasonic FMs.

PlainBill

[el3ctroded]

Re: Samsung LN-S3251D

No it's not really normal because that part should have a minimum 56dB ripple rejection at 120hz 300mA. Since it's oscillation, I'm going to say: Replace it and lets see what happens.

If it was just noise, I'd be more likely to ignore it...

Edit: Plain Bill beat me to the punch. I didn't really think the ESR was a problem (but I didn't check out what kind of caps they were supposed to be), so he is likely right. Might as well replace the caps and regulator while you're at it.

[el3ctroded]

Re: Samsung LN-S3251D

And if you need something powerful enough to easily remove that regulator but don't want to spend a lot of money, you can use this with the hot-air tip:
http://www.amazon.com/Triggertorch-3.../dp/B000HAT47S

[Sam I Am]

Re: Samsung LN-S3251D

Good grief.... pulled the main board out and on the bottom side are 8 more regs.
Got to figure out how to power it up now without shorting anything out.
Oh well.... live and learn.

[Sam I Am]

Re: Samsung LN-S3251D

To those who may be facing similar issues with this particular set or a similar model.
It is definitely a main board related problem. It took me almost two months and the acquisition of a couple of so-called "fully functional boards" to locate a properly working main board (used of course). I don't believe I have ever been this thrilled to see a solid blue screen.
At some point in time, I will try to determine the exact cause of my original main board malfunction. At which time, I will post the results.
Thank you to those on this forum for the assistance given me.

[meshje]

Re: Samsung LN-S3251D

nice to find some info on the LN-S3251D!

[truep]

Re: Samsung LN-S3251D

I had the same set and had to replace the main board as well. There are several do be sure to get the right one as they aren't compatable. They used two different panels on this set. one from Phillips, and on from chumwua.