LN-S2551D Blinks 4 Times..No Video, Sound Or Backlight

[n1iwv]

Hello:
I've been using this site for awhile to help me resurrect TVs and monitors.
It's a great resource
This is my first time posting.
My goal is to get this TV working, but more importantly, I am trying to learn something to improve my troubleshooting skills along the way.
Symptoms: LN-S2651D Chassis GBD26KU
As soon as I plug the TV into AC the power light will flash 4 times ( 1 flash per second) and then extinguish. After approx. 5 seconds, the cycle will repeat endlessly.
Pushing the power button (I don't have the remote) does nothing. I get no sound, picture or back light.

Observations:
Several components (tuner, Main CPU) on the main board (BN97-00827A) are warm to the touch.
The capacitors on the power supply (BN96-03060A) do not appear to be bulging or vented.
I have not removed them to test…yet.
When I unplug connector cm1001 from the main board, the back light will come on. They stay for the entire 4 light blinking cycle and briefly extinguish at the beginning of the next blinking cycle and then come back on.

I managed to get a copy of the service manual and followed the first troubleshooting flow diagram (see attached). All voltage test points check out until I can to box #6.
These are the voltages I say:

Location-------Should Be------------Actual

C108------------B9V----------------13.30V
C110------------B8V-----------------7.99V
C123------------VCC5VP-------------.299V
C128------------B3.3V_1-------------3.36V
C135------------B3.3V_2-------------3.32V
C133-------------5V_VCC-------------5.37V

Clearly I am not seeing 5 volt VCC and C109 is high (13.30V)
I looked on the back of the main board and located IC 103 (4435B). It appears to be a MOSFET power switch for the 5 V VCC rail. I checked the voltages on the pints of IC 103:

Pin# Value

1---5.38V
2---5.38V
3---5.38V
4---5.32V
5---.295V
6---.295V
7---.295V
8---.292V

In the picture you can see I flipped the power button PC board over so I could access the power button and see the led when the TV is face down on the bench.
When I press the power button, I can see the 3.3V present on the cable (yellow wire) go to ground.
I was able to get a main board schematic for a LN-S3292D. I thought it may be similar to the LN-S2651D
I am unable to trace how the signal for the power button translates into turning on IC 301 and providing power to the 5 volt rail.
There is a transistor Q 101 next to IC 103. I see 5.3 volts on the collector and 0 volts on the base and emitter. I see nothing on the base when I push the power button.

Assumptions:

I believe that the power supply if OK. It seems to be providing 6.2 V standby, as well as 12V, 5V and 24V.

The main reason for no 5V VCC is that IC-301 is not switching on the 5 volt rail, but on this I am not sure.

Any further things that you guys can suggest that I test would be greatly appreciated.

[tom66]

Re: LN-S2551D Blinks 4 Times..No Video, Sound Or Backlight

Many Samsung TVs have over-voltage detect circuits. The 13.3V should be 9V. Usually there's a device like a 7809 voltage regulator for dropping a 13V input (typical Samsung use 13~16V for one rail, 5~5.4V for other rail.) If the device fails short, then the 9V will be too high.

[n1iwv]

Re: LN-S2551D Blinks 4 Times..No Video, Sound Or Backlight

Thanks for the quick reply.
It appears I was measuring the 9 volts from C106 not C108 as required in the troubleshooting flow chart.
I flipped the main board over and found IC 101 (78M09A) and measure:

pin#1----13.24V
pin#2----.0002V
pin#3----9.01V

So I went back to the front of the board and located C108 right in the opposite side of IC 101 and it measures 9.01 V.
Sorry for the mistake, but these old eyes aren't what they use to be.
I rechecked all my other test points to be sure that they were measured from the correct point on the board.

[n1iwv]

Re: Samsung LN-S2551D Blinks 4 Times..No Video, Sound Or Backlight

[QUOTE=n1iwv;347884]Hello: I have made changes to my original post to correct reading at C108 and add Samsung as the manufacturer of the TV.
I’ve been using this site for awhile to help me resurrect TVs and monitors.
It’s a great resource
This is my first time posting.
My goal is to get this TV working, but more importantly, I am trying to learn something to improve my troubleshooting skills along the way.
Symptoms: LN-S2651D Chassis GBD26KU
As soon as I plug the TV into AC the power light will flash 4 times ( 1 flash per second) and then extinguish. After approx. 5 seconds, the cycle will repeat endlessly.
Pushing the power button (I don’t have the remote) does nothing. I get no sound, picture or back light.

Observations:
Several components (tuner, Main CPU) on the main board (BN97-00827A) are warm to the touch.
The capacitors on the power supply (BN96-03060A) do not appear to be bulging or vented.
I have not removed them to test…yet.
When I unplug connector cm1001 from the main board, the back light will come on. They stay for the entire 4 light blinking cycle and briefly extinguish at the beginning of the next blinking cycle and then come back on.

I managed to get a copy of the service manual and followed the first troubleshooting flow diagram (see attached). All voltage test points check out until I can to box #6.
These are the voltages I say:

Location-------Should Be------------Actual

C108------------B9V---------------- 9.01V
C110------------B8V-----------------7.99V
C123------------VCC5VP-------------.299V
C128------------B3.3V_1-------------3.36V
C135------------B3.3V_2-------------3.32V
C133-------------5V_VCC-------------5.37V

Clearly I am not seeing 5 volt VCC.
I looked on the back of the main board and located IC 103 (4435B). It appears to be a MOSFET power switch for the 5 V VCC rail. I checked the voltages on the pints of IC 103.

Pin# Value

1---5.38V
2---5.38V
3---5.38V
4---5.32V
5---.295V
6---.295V
7---.295V
8---.292V

In the picture you can see I flipped the power button PC board over so I could access the power button and see the led when the TV is face down on the bench.
When I press the power button, I can see the 3.3V present on the cable (yellow wire) go to ground.
I was able to get a main board schematic for a LN-S3292D. I thought it may be similar to the LN-S2651D
I am unable to trace how the signal for the power button translates into turning on IC 301 and providing power to the 5 volt rail.
There is a transistor Q 101 next to IC 103. I see 5.3 volts on the collector and 0 volts on the base and emitter. I see nothing on the base when I push the power button.

Assumptions:

I believe that the power supply if OK. It seems to be providing 6.2 V standby, as well as 12V, 5V and 24V.

The main reason for no 5V VCC is that IC-301 is not switching on the 5 volt rail, but on this I am not sure.

Any further things that you guys can suggest that I test would be greatly appreciated.

Thanks

[n1iwv]

Re: Samsung LN-S2551D Blinks 4 Times..No Video, Sound Or Backlight

Replaced Ic 103 (4435B / mosfet power switch) and still no joy.
The set continues to recycle with 4 blinks on the power indicator and never enters standby mode.
After looking at the power schematic for ln-s3292d (which seems similar to my set) it seems that IC 103 would never switch on until it received the SW_PVCC signal from IC201.
The fact that the set continues to cycle through attempts to enter standby mode leads me to believe it has something to do with IC-206 (DS1834AS/T,R)
Its job is to monitor the 5v and 3.3v supplies (see data sheet attached.
I measure the voltages on this 8 pin device and

pin 1----5.07V
pin 2----3.295V
pin 3----5.06V
pin 4----0.00V
pin 5 ---5.04V
pin 6----0.0V
pin 7----3.04V
pin 8----3.87V

I've attached the schematic for the ln-s3292d and the data sheet for IC 206.
Clearly the 5v and 3.3v supplies are present, but the set endlessly resets and attempts to enter into standby mode.