Samsung LN-S3251D

[el3ctroded]

Re: Samsung LN-S3251D

LDO is a specific type of linear regulator: Low Dropout. Which means that if it's a 5V regulator, you can give it 6V and it still works (or less depending upon several factors), whereas a non LDO linear regulator is going to need at least 6.5V-7V to operate.

Linear Regulators are regulators that generate the required voltage by dissipating the excess voltage as heat. A switching regulator does not do that, but "switches" the current on and off at a high frequency. After that... well, that's beyond this post...

It may be connected to the heatsink, it may not, all depends upon how much current it's expected to deliver. It doesn't have to be on the PSU either...

I assume you don't have a scope? So finding it's going to be difficult.

[Sam I Am]

Re: Samsung LN-S3251D

Incorrect assumption.
I picked one up some months back knowing it was a "required" tool. It's a older model Phillips. But you know what they say about tools.... they are only as good as the operator.
Regardless, I have no idea what a "linear regulator" looks like or on which board in this set it may be found.
So.... some direction would be greatly appreciated.

[el3ctroded]

Re: Samsung LN-S3251D

They come in all sizes and shapes and pinouts. TO90, TO220, SOT23-5, SOT223, etc.

The most common for any significant amount of current is a TO220 mounted to a heatsink. If you can get part numbers I can help figure out which pins to test for what.

[Sam I Am]

Re: Samsung LN-S3251D

Is there a particular designator (ie. QP, DP, BD, etc.) that Samsung uses to distinguish this component on the PCB?

[PlainBill]

Re: Samsung LN-S3251D

Is there a particular designator (ie. QP, DP, BD, etc.) that Samsung uses to distinguish this component on the PCB?

It will probably be either U or IC.

There are often quite easy to pick out in pictures. (HINT!!!)

PlainBill

[Sam I Am]

Re: Samsung LN-S3251D

Hope the attached pic is helpful.
IC 1 is a F9222L; designated as ICM801S on the PCB.
IC 2 is a MC33167T; designated as ICM852 on the PCB.
IC 3 is a KIA278; designated as ICM853 on the PCB.
I am still uncertain as to what is meant by a "linear regulator"!
Maybe some other term by which it is known?

[el3ctroded]

Re: Samsung LN-S3251D

I am still uncertain as to what is meant by a "linear regulator"!

http://en.wikipedia.org/wiki/Linear_regulator

[PlainBill]

Re: Samsung LN-S3251D

Hope the attached pic is helpful.
IC 1 is a F9222L; designated as ICM801S on the PCB.
IC 2 is a MC33167T; designated as ICM852 on the PCB.
IC 3 is a KIA278; designated as ICM853 on the PCB.
I am still uncertain as to what is meant by a "linear regulator"!
Maybe some other term by which it is known?

Those aren't the ones possibly responsible. On the main pc board and probably on the tcon board are three or four pin regulators. One of these is responsible.

I've circled two of them in the attached picture.While this is the logic board from a monitor, it should give you an idea of what you are looking for.

PlainBill

[tmwalsh]

Re: Samsung LN-S3251D

eradicated.

[Wizard]

Re: Samsung LN-S3251D

Not on power board. I'm talking about linear regulators on the main board itself.
Your power supply is doing fine. I have seen this noise before due to oscillating linear regulator due to bad capacitor or bad regulator itself.

Cheers, Wizard

[el3ctroded]

Re: Samsung LN-S3251D

Take a picture of your main board (top and bottom) and it should be easy to pick out the regulators on it.

[Sam I Am]

Re: Samsung LN-S3251D

Sheesh.... That info would have been nice to have earlier as it is readily obvious I did not have a clue on which board I should be looking.
Here are a couple of pics of the main board.
Thanks in advance for everyone's assistance.

[el3ctroded]

Re: Samsung LN-S3251D

To the right of the big black chip STP03 is a 5-legged surface mount part. There's another one nearby. Those are LDO Linear regulators.

Check all the caps in this area for high ESR. Using your scope, set it a 1V/div and 1ms/div. Now Check Pin 4 for output voltage. Pin 1 is the one on the same side as the text is justified at.

[PlainBill]

Re: Samsung LN-S3251D

Sheesh.... That info would have been nice to have earlier as it is readily obvious I did not have a clue on which board I should be looking.
Here are a couple of pics of the main board.
Thanks in advance for everyone's assistance.

Red circle - primary candidate

Blue circle - less likely, probably a switcher.

Part numbers will help us give you more information.

PlainBill

[el3ctroded]

Re: Samsung LN-S3251D

Yep, the red circles are the one I was talking about. They are SC1565 LDO regulators, with pin4 as the output.

Here is the datasheet for them:

Edit typo

[Sam I Am]

Re: Samsung LN-S3251D

Aside from probe issues and equipment failure, I can finally get back on this set....
The "five leggers" are SC1566's and if I am reading this scope right @ 1V/div and 1ms/div., Pin #1 is 3.3V while Pin #4 is 1.2V on both LDO's. In addition, ESR readings of all caps within the immediate vicinity are anywhere from .49 - 1.8.
The most frustrating part is for the last day or so I have been unsuccessful in acquiring a distinct signal pattern. I tired of seeing this #%$@&! "flat line".
More than likely its operator ERROR.

Soooo..... until I can figure that out......

[el3ctroded]

Re: Samsung LN-S3251D

Well, flat line is the correct thing for reading DC voltage However you would want to adjust the time/div looking for excessive noise in the voltage rail or look for oscillation in the dc.

1.8ohms seems a little high to me.

[Sam I Am]

Re: Samsung LN-S3251D

Yep.... flat line is DC whereas AC would be a waveform.
More confusion on my part.
Will need to research further about the ESR on the SM caps. Don't know what the acceptable limits should be at this point. Also was informed that I should check both sides of the cap with respect to Pin #5.
So.... in your opinion, am I on the right track as far as determining the issue with this set or do I need to look elsewhere?

[PlainBill]

Re: Samsung LN-S3251D

Yep.... flat line is DC whereas AC would be a waveform.
More confusion on my part.
Will need to research further about the ESR on the SM caps. Don't know what the acceptable limits should be at this point. Also was informed that I should check both sides of the cap with respect to Pin #5.
So.... in your opinion, am I on the right track as far as determining the issue with this set or do I need to look elsewhere?

You are in the right area, but I suspect your technique is wrong. Use AC coupling on the input (check the output voltage with a DMM first), then increase the sensitivity until you start seeing a waveform, even if it's nothing but noise.

I'm not sure, but it also looks like there are more regulators on that board.

PlainBill

[Sam I Am]

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....