Samsung LNT4069FX/XAA no picture with sound

[budm]

Re: Samsung LNT4069FX/XAA no picture with sound

BTW, I looked at the formula for calculating the output voltage on the spec sheet, it looks wrong, it should be R2/R1 not R1/R2. The higher the R2 will cause more voltage of the ADJ pin to be be higher with ref to ground, thus higher output voltage, it works the same as LM1117 series except that it has Enable pin to turn the output on and off, unless this regulator does not function the same as the LM1117 series.
IC107 is an adjustable regulator since it has 5 pins, the fixed regulator per spec sheet will only have 3pins, so retiredcaps is correct, the output of pin 4 is wrong, too low, it should be around 2.5V

[retiredcaps]

Re: Samsung LNT4069FX/XAA no picture with sound

location -IC107 FRC board
37302WU
0735
pin 1= 3.415
pin 2= 3.415
pin 3= 0.0
pin 4= 1.847
pin 5= 1.265


Base on your analysis, it looks like I should be ordering the following part:
http://www.digikey.com/product-detai...6-5-ND/1029402

IC107 is bad. Pin 4 is too low and that might be causing circuits on that board not to turn on the screen. As I mentioned, the VOUT for an adjustable regulator should be the voltage on the ADJ pin + 1.25V.

That is the correct part.

If you desolder it, you can verify it is bad.

1) Put 2 AA batteries in series for a total of 3V DC.

2) Connect the AA positive terminal to pin 2 (VIN).

3) Connect the AA negative terminal to pin 3 (GND).

4) Put your multimeter red probe on pin 4 (VOUT) and black probe on pin 3 (GND).

5) If it is working correctly, pin 4 should read 1.25V DC because your ADJ is 0.0V.

6) In this post, I show how to test a 3.3V fixed regulator.

https://www.badcaps.net/forum/showpo...22&postcount=7

7) Budm beat me to it while I was editing, re-editing, etc.

[retiredcaps]

Re: Samsung LNT4069FX/XAA no picture with sound

BTW, I looked at the formula for calculating the output voltage on the spec sheet, it looks wrong

That is something I would have never figured out.

IC107 is an adjustable regulator since it has 5 pins, the fixed regulator per spec sheet will only have 3pins, so retiredcaps is correct, the output of pin 4 is wrong, too low, it should be around 2.5V

Funny, I was just looking back at a monitor that has been sitting in my basement for 2 years. I still haven't figured out what is wrong with it, but I learned all about voltage regulators from PlainBill.

https://www.badcaps.net/forum/showthread.php?t=10228

[ceconomon]

Re: Samsung LNT4069FX/XAA no picture with sound

Does anyone have tips for removing the regulator?

I used Chip Quik to desolder the pins. I can't get the base off the board. Are these glued or soldered on to the board?

[retiredcaps]

Re: Samsung LNT4069FX/XAA no picture with sound

Does anyone have tips for removing the regulator?

In post #22, point #6, I talk about how I do. Having a 3.2mm chisel tip also helps.

[ceconomon]

Re: Samsung LNT4069FX/XAA no picture with sound

I replaced the regulator today and unfortunately it did not resolve the problem.

I took the following measurements with the replacement regulator installed. They don't appear to be any different from the the previous measurements.

location -IC102 FRC board
37302WU
0735
pin 1= 3.432
pin 2= 3.431
pin 3= 0.0
pin 4= 2.478
pin 5= 1.241


location -IC107 FRC board - part was replaced
37302WU
1105
pin 1= 3.437
pin 2= 3.436
pin 3= 0.0
pin 4= 1.837
pin 5= 1.264

Do we have any more ideas on this one?

[tom66]

Re: Samsung LNT4069FX/XAA no picture with sound

Does the regulator get hot? (too hot to touch?)

[ceconomon]

Re: Samsung LNT4069FX/XAA no picture with sound

The regulator is cool to the touch.

[retiredcaps]

Re: Samsung LNT4069FX/XAA no picture with sound

I replaced the regulator today and unfortunately it did not resolve the problem.

I don't know if anyone does it, but I always test the old part and the new part out of circuit to verify things work properly.

[retiredcaps]

Re: Samsung LNT4069FX/XAA no picture with sound

1) There are 4 caps around IC107. Which one or ones (using the positive leg) have continuity to pin 4?

2) Can we get a close up picture of that area (IC107)? Front and backside.

[ceconomon]

Re: Samsung LNT4069FX/XAA no picture with sound

I setup the battery test on the old voltage regulator and I'm not seeing any voltage on pin 4.

C104 has continuity to pin 4 on the regulator.

[tom66]

Re: Samsung LNT4069FX/XAA no picture with sound

You need to connect the on off pin too.

[momaka]

Re: Samsung LNT4069FX/XAA no picture with sound

I'm not really an expert with linear regulators like budm and retiredcaps are, so I can't say if that regulator is bad or not. However, I was wondering if the problem could be possibly caused by something else. Particularly, have a look at this picture again on page 1:
https://www.badcaps.net/forum/attach...6&d=1341687191
On the lower right corner, there are a bunch of SMD ferrite beads that look very charred. Or perhaps that is dirt/flux - I can't tell for sure.

My suggestion would be to try and clean that part of the board with isopropyl alcohol and retake another picture of the area. Also, check all of the ferrite beads with your multimeter - those are the components labeled with BDxxx (where xxx is a number). Personally, I've never seen one go bad, but it should take just a few minutes so might as well do it. To test those ferrite beads, set your multimeter to measure resistance (if you're using a manual multimeter, set to the lowest resistance scale - usually 200 Ohms) and check the resistance across the bead - it should read very low Ohms or ideally zero ohms and not "1" on the left side of the screen or "OL".

Also, there's quite a bit of discoloration on the board from those linear voltage regulators. Just FYI, about 2 weeks ago I bought a TV on craigslist in "as-is" condition. TV would power but display lots of random colored pixels on the screen. As it warmed up, the random colored pixels would slowly disapear and the picture would go back to normal. I found the problem to be bad BGA joints on a RAM chip caused by excessive heat from nearby linear voltage regulators (they were actually right under the RAM chip, just on the other side of the board). Whoever designed that main board is either a moron or a planned obsolescence design genius.

With that said, I think your problem could also be cracked BGA joints. Looking at this picture,
https://www.badcaps.net/forum/attach...5&d=1341687191
it seems there are 3 BGA chips in the upper right corner of the board (one is under a small heat sink). If nothing seems to fix the board, you could try reflowing those BGA chips. Oven reflow method may not work due to all of the caps on the board, but hot air (mostly from the underside and then a bit on the top side) may work.

The last thing I can think of is if some of those caps next to those voltage regulators have gone bad due to the excessive heat. But for that you'll need to have an ESR meter to check them with.

For now, just try cleaning the board in that area I mentioned and see if those ferrite beads are good.
I hope this helps in some way.

[ceconomon]

Re: Samsung LNT4069FX/XAA no picture with sound

You need to connect the on off pin too.

I'm not understanding you. I assume you are refering to the testing of the voltage regulator.

Battery + =pin2
Battery - =pin3 (ground)
Measure voltage from pin4 to pin3(ground) to test

Where is the on/off pin?

[budm]

Re: Samsung LNT4069FX/XAA no picture with sound

If you look at the spec of that 5-pin regulator IC, PIN1 is an ENABLE pin to turn the output ON/OFF. Please see the spec sheet.

[ceconomon]

Re: Samsung LNT4069FX/XAA no picture with sound

If you look at the spec of that 5-pin regulator IC, PIN1 is an ENABLE pin to turn the output ON/OFF. Please see the spec sheet.

The spec sheet did nothing for me at my current level of knowledge. What would I connect the enable pin to complete the circuit?

[ceconomon]

Re: Samsung LNT4069FX/XAA no picture with sound

I cleaned the back of the mainboard with alcohol. I've examined that area throughly with a magnifying glass and I can't determine the source of that mess. It looks like flux to me. Here are the new pictures.

All of the ferrite beads tested good.

[budm]

Re: Samsung LNT4069FX/XAA no picture with sound

EN pin1 to pin2 Vin. Are the regulator you are checking has 5 pins?

[ceconomon]

Re: Samsung LNT4069FX/XAA no picture with sound

EN pin1 to pin2 Vin. Are the regulator you are checking has 5 pins?

The regulator does have 5 pins and the data sheet confirms pin1=EN and pin2=VIN.

That explains why the measurements on pin1 and 2 were the same on my previous test.

After connecting pin1 and pin2, I'm measuring 3 volts on pin4. That doesn't make sense to me. It was measuring lower than the input voltage before.

[budm]

Re: Samsung LNT4069FX/XAA no picture with sound

When you test the adjustable regulator, you will need to attach two resistors, one will be between output pin and the ADJ pin, another one will be between the adj pin and ground.
The output voltage will have to be calculated using the formula.
The fixed regulator does not need the external resistors since they will be inside the regulator. The fixed regulator will have number such as 33 after the regulator P/N to indicate the output voltage, in this case, 33 means the regulator is a 3.3V regulator.
What kind of P/N is on the regulator?