Samsung LN40A550P3FXZA video not working

[ElSebas82]

Hello,

I have a LN40A550P3FXZA. When you turn the TV on, everything works perfectly. Then, after maybe 5 minutes or as long as 2 hours or whatever time (not regular), the screen goes completely off (no glare, no stripes, nothing, just like if it was off), but the audio keeps going. Turning it off and back on works very rarely. Most of the time I need to let it sit for a couple of minutes at least. And when I turn it back on, it happens again. One thing I've noticed is that the failure occurs faster if I am watching cable (directly connected to the back, no box), and even faster if it is an HD channel. Component seems to work a little longer and HDMI the longest of all inputs I've tried.

The capacitors on the power board look good, though I have already read that even if they look good they may not be working. Also, I am pretty sure these are not the original capacitors (I bought the TV from a friend who was getting rid of it about 2 years ago).

The boards I have are:
- Power: SIP408A (3925310014AD)

- Main: PEARL BN41-00975B(2008.01.13) (on the board)
BN97-01985T (on sticker)
BN94-01628T (sticker on top of "heat sink")
AA40-00177A / TDQU6-K01A / 8215M17G (on cable connector)

I am attaching some pictures showing all boards.

Any help would be very helpful!!

Sebastian

[budm]

Re: Samsung LN40A550P3FXZA video not working

So the backlights go off? I would inspect the solder joints on the power supply board and the cabel really well first, also need to monitor the BL-ON pin to see if it is still present when the backlights go off.

[CapLeaker]

Re: Samsung LN40A550P3FXZA video not working

also check if the 24V going to the inverter board is present when the backlight turns off and the sound keeps on playing.

[ElSebas82]

Re: Samsung LN40A550P3FXZA video not working

Hi guys! Thanks for the replies. I am at work, so I'll be able to check all this tonight However, in the meantime, I have some extra questions as I am not very familiar with the terminology:

So the backlights go off? I would inspect the solder joints on the power supply board and the cabel really well first, also need to monitor the BL-ON pin to see if it is still present when the backlights go off.

- The backlights refers to the white light you see from the back of the screen? If so, I am almost positive they do go out but will confirm later. If that is not what you were talking about, please let me know.

- Solder joints on the power supply board... The line voltage goes to a small plug on the lower right corner of the board, then it goes to a transformer. Which solders are you talking about? All soldered components on the board?

- BL-ON pin... Now I am really lost, lol. What is this exactly?

also check if the 24V going to the inverter board is present when the backlight turns off and the sound keeps on playing.

This I know how to check (at least one )

Seba

[budm]

Re: Samsung LN40A550P3FXZA video not working

"- The backlights refers to the white light you see from the back of the screen? " Yes, it is the light source so you can see image on the screen.

"- Solder joints on the power supply board... The line voltage goes to a small plug on the lower right corner of the board, then it goes to a transformer. Which solders are you talking about? All soldered components on the board?" The solder connections of the component's to the copper pads on the circuit board.

"- BL-ON pin... Now I am really lost, lol. What is this exactly?" It is the command signal from the main board to turn on the backlights circuit, <1VDC = OFF, >2.5VDC = ON.
What kind of tools do you have? You will be making Voltage checking in the deadly side of the circuit, so if you are not sure what you are doing, I suggest you not to do it.

[ElSebas82]

Re: Samsung LN40A550P3FXZA video not working

Hi again. Here's the update:

- Backlights: They do turn off when it fails.

- Solder joints: Everything looks pretty great. I took some pictures of the back of the power supply board. Now it is confirmed these are not the original capacitors. You can see where they were soldered (not the best job, but they are connected)

- BL-ON pin: I am still not sure which pin this is on the board. I did measure:
CN801, pin #1: 4.31 VDC before and after the failure.
CNI803, pin #1: 4.91 VDC before and after the failure.

- Power to inverter board: There is only 12V going to the inverter board and I checked it at 11.43V before and after the failure.

New development. Before I started testing voltages, it had started having the failure while connected to the cable as soon as I tried to change the channel. This is how I was checking the voltages. Turn it on, check voltage, change channel, screen goes blank, check voltage again, turn it off and start all over again.

However, now when I turn it on, it only last maybe 3 seconds with the screen on and then automatically goes blank. I am fairly sure I did not mess up anything that was not messed up to begin with. It seems that it is getting worse though.

I have a multimeter and I am using needles to jam on the connectors so I can test the voltage on each pin without unplugging the connector. Don't worry, I put them on while the tv is off and unplugged and after I have discharged all capacitors that might shock me.

Thanks budm and CapLeaker for your help. Any more things I should check?

Seba

[budm]

Re: Samsung LN40A550P3FXZA video not working

"Power to inverter board: There is only 12V going to the inverter board and I checked it at 11.43V before and after the failure." That long board is not inverter board, it is Balancer board, your TV has power supply/inverter board combination. The 12VDC (VCC) feeding the Balancer board is for running the fault detection circuit.
The LD (Lamp Detection, >10V = good) and FB (Feedback, lamp current, will be in mVAC) are signals for telling the main board if there are problems with the LAMPS circuit.
Connector CNI803 pin 1 (pin has White Triangle marking) is the INVERTER -ON/OFF pin, it should have >2.5V, and per your report "CNI803, pin #1: 4.31 VDC before and after the failure." so BL-ON is OK.
"CN801, pin #1: 4.31 VDC before and after the failure." PS-ON is also OK.

So check LD pin to see if it goes >10VDC and then drops down or not.
BTW, lots of solder joints do not look good.

[ElSebas82]

Re: Samsung LN40A550P3FXZA video not working

The LD (Lamp Detection, >10V = good)

Before failure 9.82 VDC. After Failure 10.08 VDC

Both pins labeled LD

FB (Feedback, lamp current, will be in mVAC)

Before failure ~0.190 VAC. After Failure 0 VAC

Both pins labeled FB

BTW, lots of solder joints do not look good.

Fixing all these solders might be a bit too much for my soldering skills. But just out of curiosity, how would you go around fixing these properly?

Again, thank you so much for your help budm!

SEBA

[CapLeaker]

Re: Samsung LN40A550P3FXZA video not working

Fixing all these solders might be a bit too much for my soldering skills. But just out of curiosity, how would you go around fixing these properly?
SEBA

reflow the solder joint with your soldering iron and a very small amount of fresh solder, or you take the old solder off with a solder sucker or a solder wick and resolder the joint with all fresh solder.

So I take it that the condition changed. Now the TV turns off after 3 seconds. Can we get a full set of measurements with the pin names beside it?

[ElSebas82]

Re: Samsung LN40A550P3FXZA video not working

Hi,

Well, quick update on status. I have it connected only to HDMI and cable. The HDMI works fine for some time (I have not left it too long, but it will go easily for 5 minutes). However, once I put it on cable, it will only last a couple seconds until the video goes out. Then I have to wait at least some 5 minutes to turn it back on. I made short video of this (music video is plating through HDMI from my computer ): https://www.youtube.com/watch?v=0oJTzEiKsYM

CapLeaker: This is what I have measured so far.

CN801, pin #1: 4.31 VDC before and after the failure. (PS-ON)
CNI803, pin #1: 4.91 VDC before and after the failure. (INVERTER -ON/OFF)
LD (both pins): 9.82 VDC before failure, 10.08 VDC after failure.
FB (both pins): ~0.190 VAC before failure, 0 VAC after failure.

Thanks everyone for the help! Any other idea of what to check next to try to troubleshoot this thing?

SEBA

PS: Anyone knows what this button on the top right corner of the main board is supposed to do?

[ElSebas82]

Re: Samsung LN40A550P3FXZA video not working

Hi,

Here is as a comprehensive set of measurements as I could put together:

CN801 pin #1 POWER ON/OFF: Before 4.3, After 4.31
CN801 pin #2 SYNC: Before 1.654, After 1.652
CN801 pin #3 STB5.3V: Before 5.08, After 5.08
CN801 pin #4 GND: Before N/A, After N/A
CN801 pin #5 GND: Before N/A, After N/A
CN801 pin #6 GND: Before N/A, After N/A
CN801 pin #7 13V: Before 12.84, After 12.86
CN801 pin #8 13V: Before 12.85, After 12.85
CN801 pin #9 GND: Before N/A, After N/A
CN801 pin #10 GND: Before N/A, After N/A
CN801 pin #11 GND: Before N/A, After N/A
CN801 pin #12 GND: Before N/A, After N/A
CN801 pin #13 5.3V: Before 5.03, After 5.04
CN801 pin #14 5.3V: Before 5.04, After 5.04
CN801 pin #15 5.3V: Before 5.04, After 5.04
CN801 pin #16 5.3V: Before 5.04, After 5.05
CN801 pin #17 GND: Before N/A, After N/A
CN801 pin #18 GND: Before N/A, After N/A
CN801 pin #19 13V: Before 12.85, After 12.86
CN801 pin #20 GND: Before N/A, After N/A
CN801 pin #21 13V: Before 12.85, After 12.87
CN801 pin #22 13V: Before 12.87, After 12.86
CN801 pin #23 NC: Before N/A, After N/A
CN801 pin #24 NC: Before N/A, After N/A
CN801 pin #1 INVERTER ON/OFF: Before 4.88, After 4.91
CN801 pin #2 NC: Before N/A, After N/A
CN801 pin #3 PWN DIM: Before 5.16, After 5.15
CN801 pin #4 GND: Before N/A, After N/A
CN801 pin #5 DET_5V: Before 5.04, After 5.04
CN801 pin #1 12V: Before 11.23, After 11.43
CN801 pin #2 FB [VAC]: Before 0.192, After 0
CN801 pin #3 FB [VAC]: Before 0.192, After 0
CN801 pin #4 GND: Before N/A, After N/A
CN801 pin #5 GND: Before N/A, After N/A
CN801 pin #6 LD: Before 9.88, After 10.06
CN801 pin #7 LD: Before 9.88, After 10.05
CNI801: Could not measure it
CI822: Before 12.85, After 12.86
CM801: Before 3.1, After 3.1 (it discharges slowly as I measure it but comes back to about 3.1)
CM802: Before 20, After 19.2
CM803: Before 3.1, After 3.1 (it discharges slowly as I measure it but comes back to about 3.1)
CM804: Before 13.13, After 13.09
CM806: Before 13.12, After 13.09
CM808: Before 12.89, After 12.88
CM809: Before 5.1, After 5.09
CM810: Before 5.06, After 5.06
CM812: Before 5.1, After 5.1
CM813: Before 5.1, After 5.09
CM814: Before 14.68, After 14.63
CM815: Before 15.2, After 15.14
CP801: Before 14.36, After 9.49
CP802: Before 378, After 166.7
CP803: Before 378, After 166.5
LM801 [mVDC]: Before 9.5, After 8.6
LM802 [mVDC]: Before 14.5, After 12.3

I had the TV running on HDMI for about 2 hours and then switched to Cable and got the failure after a couple of changing channels (as opposed to changing channel only once like on the video I posted). Then got TV back on and it seemed to do the same. Now I was able to put it on Cable for over 30 minutes even changing channels until finally I got the failure...

Any ideas guys?

SEBA

[CapLeaker]

Re: Samsung LN40A550P3FXZA video not working

The only drastic change happening is CP801: Before 14.36, After 9.49

If you run the tv with the back off in a regular warm, but not hot room and let a fan blow on the main board. Does that lengthen the HDMI viewing time?

[ElSebas82]

Re: Samsung LN40A550P3FXZA video not working

The only drastic change happening is CP801: Before 14.36, After 9.49

Is this an indication of anything? I have been trying to find a wiring diagram to see what each capacitor is supposed to be there for.

If you run the tv with the back off in a regular warm, but not hot room and let a fan blow on the main board. Does that lengthen the HDMI viewing time?

Ever since the first message in this thread I've run the TV with the back off. The temperature in the room is between 72F and 76F (22C to 24.5C). Today I left the TV on for about 4 hours on HDMI with no problems (with video playing the whole time). After that, I switched to cable and changed channels for like 5 minute at least until it finally failed and the image went out.

Just a note, it does fail with HDMI. However, it never is after a definite time. Sometime it has lasted 5 minutes, other 30 and other it never fails for hours.

My first thought was initially a temperature issue, but after this long of running it and making it fail seconds after turning it on while changing channels or being able to change channels for a while without issues, I don't think it is temperature (though I might be wrong of course).

Any ideas of what could be to blame for this? Am I beating a here?...

Thanks for your input!

SEBA