Samsung PN50C8000 Plasma Screen Goes Black

[jshaia]

Hi! I am a new member looking for some help. Thanks in advance.

I have a Samsung PN50C8000 plasma TV. I have looked through several forums and thread to try to identify the problem, but I am not quite able to do so. Some help would be greatly appreciated.

Here's the problem: When I turn the TV on, I get normal picture and sound. After less than 5 minutes, the picture goes completely black - not just the dark grey you get when the display is working but there is no signal. The picture does not come back. However, if I turn the TV off and on again, the picture and sound are both fine for a few minutes before I lose the picture again. Sometimes, just before the picture goes out, I will get odd repeating patterns on the display for a few seconds, e.g., random blue and pink bars. This does not always happen and it is not always the same when it does happen.

Here's what I've done so far:

1) I tried multiple inputs - all of the HDMI inputs and the component inputs. The problem is the same regardless of the input I use.

2) I tried multiple sources - a cable box and a DVD player. The problem is the same.

3) I opened up the TV and checked the key voltages - Vs, Va, Ve, and Vscan. They are all normal both before and after I lose the picture.

4) I checked the green LED on the Logic Board. When I have a picture, it flashes once a second. When I do not have a picture, it typically flashes once a second. However, sometimes, when I lose the picture, the green LED stays on and does not flash. I am not sure why it behaves differently different times.

5) I went into service mode and checked the patterns. When the picture goes out, I do not get any FBE (main board) or Logic Board patterns. Nor does the volume or the menu display (I can however adjust the volume). When I have a picture, I get the Logic Board patterns. If I have an input signal, I also get the FBE patterns. If I do not have an input signal, I do not get the FBE patterns.

6) I noticed while I was in service mode, that the T-Con checksum showed an error. It seems from forums that I have read, that this can happen and the TV can still work completely fine. I am not sure if this means anything.

7) I also checked the voltages from the Main Board to the Y sustain and the X sustain boards. Here's what I got to the Y sustain board both before and after I lose the picture:

Va - 55
RTN - 0
Vg - 15
Rtn - 0
Vs - 203
Vs - 203

To the X sustain board, from left to right, both before and after I lose the picture, I got:

15
0
0
0
203
203

8) Checked the fuses on the Y sustain and X sustain boards. Both seemed fine - 0 ohms.

My best guess: I suspect that my Main Board and my Logic Board are fine. I suspect the issue is with my Y sustain, Y buffer, X sustain, or X buffer. Assuming this is correct (I think it is, but I am not sure), I do not know how to narrow it down to one of these 4 components. I have also seen posts that say if you replace either the Y sustain or the X sustain, you should replace both. I have also seen posts that say if you replace the Y sustain, you should replace the Y buffer and the same for the X sustain.

Sorry for the long post. Any advice would be much appreciated!!

[jshaia]

Re: Samsung PN50C8000 Plasma Screen Goes Black

Sorry, I think I put one extra 0 on the voltages to the X sustain. They should be:

15
0
0
203
203

[mmartell]

Re: Samsung PN50C8000 Plasma Screen Goes Black

Run the test patterns by jumping the proper pins on the control board. This will remove the main board from the equation.

[jshaia]

Re: Samsung PN50C8000 Plasma Screen Goes Black

Thank you MMARTELL. I appreciate the reply.

I have the Fast Track Troubleshooting Manual, but I am not familiar with this process, so please let me confirm that I am about to do this correctly. Here are the instructions I have from the manual:

1) Remove power cord to panel - I get this.
2) Short highest pin #s on Logic Board Test Jig. (Can be 4 pin or 6 pin) - I think that means that I short the 3 and 4 pins on the Logic Board in the first attached picture. Please confirm
3) Remove power connector at Main Board (keeping connection to SMPS) - I get this.
4) Short "Power On" pin to Circuit Ground on Power Connector to SMPS - I assume that Power On is "PS_ON" and this is pin 1. Pins 4, 5, 6, 7, 14, and 15 are all ground. I assume it does not matter which of these I use. Please confirm. Lastly, I am going to sound really stupid here, but I want to be sure I do this correctly. The connector has two rows of connections. I assume that pin 1 is the one closest to the top of the TV and in the row closer to the back of the TV and farther from the front. Do I have this correct?
5) Connect power cord to panel - I get this.

Once I do this and I am looking at the test patterns, how will I know if I am viewing them before or after the display would go black? I will have no power to the main board, so I won't have a normal signal. I guess I can just wait for a while and assume that the display would have gone out. Is there a different approach to this?

Thanks so much.

[Alastair E]

Re: Samsung PN50C8000 Plasma Screen Goes Black

With set unplugged, Use comp hard-drive link on pins 3-4 of TP-Auto-Gen and Disconnect the LVDS from MB.

Plug set in, check for test-patterns.

[jshaia]

Re: Samsung PN50C8000 Plasma Screen Goes Black

Thank you Alastair E.

Don't I also have to short the power to ground on the connector to the Main Board? Am I correct on the pin configuration on the connector?

Thanks.

[jshaia]

Re: Samsung PN50C8000 Plasma Screen Goes Black

I found labeling for the 1 pin on the connector It looks like 2 is directly below it and then 3 is to the left as I look into the male connector. 4 is directly below 3, etc. Does that make sense?

[Terryfictv]

Re: Samsung PN50C8000 Plasma Screen Goes Black

Power on and then unplug the cable to the touch control PCB and see if it will stay running...

[jshaia]

Re: Samsung PN50C8000 Plasma Screen Goes Black

Thanks TerryficTV. I see four connectors to the touch pad PCB. One goes to the Y sustain, two are ribbon connectors that go to the Logic Board, and one goes to a narrow long PCB on the other side of the TV at the bottom edge. I think this is Buffer F. Which one are you suggesting that I disconnect? Thanks.

[tom66]

Re: Samsung PN50C8000 Plasma Screen Goes Black

There should be no cables going from the touch pad to the address buffer F, can you show us a picture??

[jshaia]

Re: Samsung PN50C8000 Plasma Screen Goes Black

Thanks Tom66.

Maybe I misunderstood what the touch pad pcb is. I assumed it's the pcb just above the touchpad in the lower corner of the TV - where the power, volume, channel switches are. I see this labeled as E Buffer in a diagram. There may be a small pcb hidden under the metal bar along the bottom of the TV that I am missing.

There appears to be a jumper between E Buffer and F Buffer - the grey and black wires in the attached pictures - at the end of F Buffer - near the middle of the lower edge of the TV.

Sorry if I am confused about what the touchpad pcb is. Thanks.

[tom66]

Re: Samsung PN50C8000 Plasma Screen Goes Black

Yes, the touchpad has the volume/channel/etc on it.

The grey cable carries the Vda supply for the address buffers (approx 50~60V DC.) At no point should this cable be disconnected unless you really know what you are doing (incorrectly reconnecting it, at the wrong time or without thoroughly discharging the supply can cause plasma panel failure.)

The touchpad cables are separate, and do not connect to the address buffer.

[jshaia]

Re: Samsung PN50C8000 Plasma Screen Goes Black

Tom66, thank you VERY much for sparing me from that potential mistake!!

[jshaia]

Re: Samsung PN50C8000 Plasma Screen Goes Black

Alastair E., I did as you suggested. I got a series of test patterns. I let them run for 15 minutes, and they never went out. There were some black specks in many of the patterns, in case that is relevant. I can't know for sure that the display would have gone out in 15 minutes with a normal signal, but it typically would not last even 5 minutes.

I am happy to also try the Fast Track Troubleshooting Manual approach of shorting the pins on the connector from the SMPS to the Main, but I suspect that is in essence the same test I just did.

Does this make the Main a suspect? Next steps? Thanks for all of the comments and help!!

[mmartell]

Re: Samsung PN50C8000 Plasma Screen Goes Black

Yes it makes the main board a suspect if you believe the screen would have gone black by then.

You may be able to verify this result by hooking everything up as normal again and getting a hair dryer. Turn the tv on and see if you can force the screen to black out quicker by spraying heat on it - first concentrate on the main ic, then work your way around. If you find a certain repeatable location that causes the fault then you've really narrowed the problem. Post back your results.

[jshaia]

Re: Samsung PN50C8000 Plasma Screen Goes Black

Thanks mmartell.

I ran several tests. Here they are:

1) I turned the TV on and blew hot air on the Main Board. It took 4-5 minutes for the display to go out - about the same as usual.

2) I turned the TV on and blew cold air on the Main Board. The display did not go out for 15 minutes. Then, I stopped blowing cold air on the Main Board. The display went out in 3 minutes.

3) I ran the test patterns with a normal signal coming in through an HDMI port. As long as I was on the Logic Board patterns, I could continue to flip through the patterns for 15 minutes, at which point I gave up. A few minutes into this, I could no longer see the service menu when I tried to go to it, and I could not access the FBE patterns. Once I leave the Logic Board patterns, I cannot get back to them once I cannot see the service menu

4) I repeated 3) with no signal attached, which means I can only use the Logic Board patterns. They continue to work for 15 minutes, at which point I gave up.

Here's my theory: blowing hot air on the Main does not do much because the additional heat is offset by a large volume of air flowing over the heat sinks. The air is somewhat cooler than the heat sink would otherwise be. There's more heat, but there's also more cooling, so I get the same result. Blowing cool air over the Main provides more air and cool air, so the display does not go out. The test pattern results also seem to be consistent with a Main Board issue.

Also, I noticed some discoloration on the sticker on the Main Board. See the attached picture.

I think it's the Main Board. What do you think?

If it is the Main, Shopjimmy is out of them. Do you recommend another vendor to try?

Thanks for your help.

[mmartell]

Re: Samsung PN50C8000 Plasma Screen Goes Black

You may be able to use one from a 50C7xxx if they use the same panel.

If this problem is heat related then you are not using enough heat in your test. Applying heat to a board which fails due to heat would never be better off by applying more heat to it. If you can find the problem area you may be able to repair it and not have to concern yourself with another one which may soon fail in the same way.

[jshaia]

Re: Samsung PN50C8000 Plasma Screen Goes Black

Thanks mmartell.

I am going off of the part number on the board, rather than the model number of the TV. I think that means that shopjimmy does not have it.

Is there another way you would suggest applying heat to the Main to test it? Are there other ways to determine if it is the Main that is the source of the problem? Of course, I could repeat the hair dryer test. I only did it once, and there is some randomness to how long it takes the display to fail. Any other tests to try?

What do you make of the fact that cooling resolves the problem and that my Main test patterns go out with the display, but my Logic Board patterns still work?

[jshaia]

Re: Samsung PN50C8000 Plasma Screen Goes Black

I tried some other tests. This time, when I used the hair dryer, I used a slower speed setting, but the same high temperature setting (I am not sure if this made a difference, but it's what I did). Here's what I did (letting the Main Board completely cool between each test):

1) I preheated the Main Board before turning on the TV. I did not provide any heat once I turned the TV on. The display only lasted 2.5 minutes, definitely less than usual.

2) I preheated the Main Board and continued to apply heat after turning on the TV. The display lasted less than a minute.

3) I did not preheat the Main Board. I heated heat sinks 1 and 2 on the Main Board in the attached pdf. It took 5 minutes before the display went out - normal time without heating.

4) I did not preheat the Main Board. I heated heat sink 3 when I turned the TV on. The display went out in less than a minute - definitely shorter than usual.

5) I did not preheat the Main Board. I heated heat sink 4 when I turned the TV on. The display went out in about a minute. I was able to get the display to come back on by removing the heat. The same was also true for applying and removing heat from heat sink 3 at this point. Eventually, the heat from the components became large enough that the display was out whether or not I was applying heat.

I unscrewed the Main Board and looked on the bottom underneath the components that have heat sinks 3 and 4 attached. I see some discoloration. See the other two attached pictures. I do not think my soldering skills are anywhere near good enough to consider replacing these chips if they are the issue.

IF YOU AGREE THAT IT IS THE MAIN BOARD (I'm not assuming that you do), I can't find a new one anywhere. I'd rather not buy used or refurbished. Anywhere I should try for a new one? If not, anywhere you trust for used/refurbished boards?

Thanks for all of the help.

[jshaia]

Re: Samsung PN50C8000 Plasma Screen Goes Black

I also found out that BN94-03313B is a substitute for BN94-03313V (my board), but I still can't find any at shopjimmy.