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Old 04-27-2020, 08:15 AM   #1
heathloder
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Default Samsung PN43E440A2F – display turns off after several minutes

I have a Samsung PN43E440A2F 43” plasma that operates normally, with the exception of the display randomly shutting off after several minutes of running (approximately 5 minutes). When the display turns off, I continue to receive audio through the optical output to an external speaker, but there is no backlight and there appears to be no image either (using the flashlight test). The audio function doesn’t seem to fail regardless of how long I leave the TV on. I’m using an external speaker because I don’t currently have access to the TV’s internal speakers (I left the speakers at the owner’s house by mistake when picking up the TV).

In this state (display off, audio still playing), the “function”/power button on the display doesn’t seem to do anything, and I don’t currently have access to the remote either, as I left that with the speakers mistakenly as well. The TV must be unplugged and plugged back in at this point to get the image to return on the display, and then the above cycle repeats, where the image will just go blank after approximately 5 minutes with the audio still playing.

There is no visible damage to any of the components on the top of the boards (X-Buffer, Y-Buffer, X/Y-Main, SMPS, Mainboard, T-Con) and I don’t smell anything funky, so I wasn’t really sure where to even start with this. I also attached the “Fast Track” troubleshooting guide that I found for this (or a very similar) model, which helps identify each of the boards in my photos.
Attached Images
File Type: jpg 20200426_115132.jpg (711.7 KB, 11 views)
File Type: jpg 20200426_115146.jpg (650.6 KB, 8 views)
File Type: jpg 20200426_115255.jpg (737.2 KB, 10 views)
File Type: jpg 20200426_115308.jpg (665.7 KB, 14 views)
File Type: jpg 20200426_115507.jpg (896.4 KB, 10 views)
File Type: jpg 20200427_093748.jpg (780.2 KB, 8 views)
Attached Files
File Type: pdf Samsung_PN43E450A1FXZA_fast_track_guide_[SM].pdf (1.25 MB, 6 views)
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Old 04-27-2020, 08:33 AM   #2
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Default Re: Samsung PN43E440A2F – display turns off after several minutes

Do you lose any of the voltages on connector CN804 when the display shuts off.
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Old 04-27-2020, 10:21 AM   #3
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Default Re: Samsung PN43E440A2F – display turns off after several minutes

Thank you for your response @dick_barton!

I just probed CN804 while the TV was operating normally, and then again when the display had cut out. The readings were as follows:

Connector CN804 (SMPS/X-Buffer):
DISPLAY ON
Pin 1 GND =
Pin 2 PS-ON = 118.9 mV
Pin 3 VS_CON = 1.45 V
Pin 4 VS-ON = 3.27 V
Pin 5 GND =
Pin 6 D5.3V = 5.23 V
Pin 7 D15V = 15.28 V
Pin 8 GND =
Pin 9 VA = 58.4V
Pin 10 NC =
Pin 11 VS = 210.5 V
Pin 12 VS = 210.5V

Connector CN804 (SMPS/X-Buffer):
DISPLAY_OFF (ERROR STATE)

Pin 1 GND =
Pin 2 PS-ON = 119.8 mV
Pin 3 VS_CON = 5.4 mV
Pin 4 VS-ON = 0.7 mV
Pin 5 GND =
Pin 6 D5.3V = 5.23 V
Pin 7 D15V = 15.19 V
Pin 8 GND =
Pin 9 VA = 120.6 mV
Pin 10 NC =
Pin 11 VS = 210 -> 0V
Pin 12 VS = 210 -> 0V

Pins 11 & 12 decreased to 0V very slowly after the screen went dark, and then I noticed for the first time that once VS hit about 0V, the TV returned to standby and I was able to power it on again using the power button on the TV, as opposed to unplugging it and plugging it back in. Behavior is still the same, however.

I don't believe it's problematic, but I do hear what sounds like a (relatively) loud transformer buzz coming from the X/Y main board, just in case that's relevant.
Attached Images
File Type: jpg 20200427_115211.jpg (405.6 KB, 4 views)

Last edited by heathloder; 04-27-2020 at 10:31 AM.. Reason: Added picture of CN804
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Old 04-27-2020, 10:43 AM   #4
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Default Re: Samsung PN43E440A2F – display turns off after several minutes

The problem appears to centre around VS_ON and VS_Con.
I think VS_ON may be switched on by the Logic board when it recieves VS_Con but I'm not sure. It could be the other way.
There's reference to it in the fast track guide above.

There's also some information in this thread

https://www.badcaps.net/forum/showth...=vs_con&page=2

Edit
There's normally an led on the logic board. What is the flashing sequence when the display goes off?

Last edited by dick_barton; 04-27-2020 at 10:49 AM..
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Old 04-27-2020, 11:05 AM   #5
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Default Re: Samsung PN43E440A2F – display turns off after several minutes

Activate the power and logic board test pattern and see if the TV stays on.
I suspect a partially cracked BGA under the main processor on the mainboard. The five minutes is the time it takes for the crack to open but the test will confirm this.
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Old 04-27-2020, 11:34 AM   #6
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Default Re: Samsung PN43E440A2F – display turns off after several minutes

Will be interesting to see what the result will be. Cheers
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Old 04-27-2020, 11:41 AM   #7
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Default Re: Samsung PN43E440A2F – display turns off after several minutes

Upon initial power-on, the logic board LED blinks for a half a second, every half a second (0.5s ON/0.5s OFF), which appears to indicate normal operation, and can be confirmed visually/audibly.

Once the display shuts off, the logic board LED starts showing a 5s ON/2s OFF pattern.

I’ve attached a page from a PDF I found that has some information about the LED patterns; not sure how authoritative it is.

I will attempt @diif’s suggestion shortly (power/logic board test patterns) and get back to you with the results. Thanks for the help!
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Old 04-27-2020, 01:11 PM   #8
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Default Re: Samsung PN43E440A2F – display turns off after several minutes

So I've jumped the PS-ON connection on the SMPS to ground using the harness that was unplugged from the mainboard, as instructed in the fast track guide, but when I went to jump the test jig pins on the logic board, I noticed that I only had two pads, instead of four (or even six), as the fast track guide suggests I would find.

My initial though was that there are probably 4 pads underneath, soldered in pairs, but I have no idea what any of the pins do, except being told that the "highest 2" need to be jumped for the test pattern to work.

I've included pictures to illustrate my issue. Does anyone know if it's safe to just jump these two points (and remove the jumper when finished), or do I need to un-bridge the existing solder connections, connect ONLY pads 3+4 for the logic board test, and then re-bridge the pads as they were when I found them?
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File Type: jpg 20200426_115255.jpg (737.2 KB, 8 views)
File Type: png Samsung_test1.png (612.2 KB, 6 views)
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Old 04-27-2020, 01:31 PM   #9
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Default Re: Samsung PN43E440A2F – display turns off after several minutes

Not pins on yours but holes (bottom left) bridge 3 and 4.

Last edited by diif; 04-27-2020 at 01:40 PM..
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Old 04-27-2020, 02:15 PM   #10
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Default Re: Samsung PN43E440A2F – display turns off after several minutes

Thanks @diif.

I managed to get the self-test to power up, and it successfully cylced through the patterns about 5 or 6 times (~4 minutes) and eventually shut down just as before, exhibiting the same 5s ON/2s OFF LED pattern on the logic board.

Does this imply that the mainboard is not causing this issue?
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Old 04-27-2020, 02:54 PM   #11
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Default Re: Samsung PN43E440A2F – display turns off after several minutes

Quote:
Originally Posted by heathloder View Post
Thanks @diif.

I managed to get the self-test to power up, and it successfully cylced through the patterns about 5 or 6 times (~4 minutes) and eventually shut down just as before, exhibiting the same 5s ON/2s OFF LED pattern on the logic board.

Does this imply that the mainboard is not causing this issue?
Yes, that test removes the mainboard and my cracked BGA theory.

When the picture went off before but sound remained. If you turned the TV off would it then turn back on properly ?
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Old 04-27-2020, 02:59 PM   #12
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Default Re: Samsung PN43E440A2F – display turns off after several minutes

Quote:
When the picture went off before but sound remained. If you turned the TV off would it then turn back on properly ?
Yes. The TV requires no "cool down" time whatsoever, and when turned back on, will remain on for almost 5 minutes again before cutting out every time. Just to clarify, once the display turns off, the function button doesn't work anymore, so I must unplug and re-plug in the unit to effectively "reboot" it.
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Old 04-28-2020, 09:35 AM   #13
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Default Re: Samsung PN43E440A2F – display turns off after several minutes

Not really knowing where to look next, I started doing some very basic and general testing on the X/Y-Main and Y-Buffer boards. I removed both boards from the TV and began with the X/Y-Main.

I tested the three MOSFETS and 2 diodes (in-circuit) that were attached to the heatsinks - they are the only FETs/diodes on the top-side of the board.

They all seemed to test OK (using the 'diode' function on my DMM).

FET Q5001:
Pin (-,+) | Reading
1-2 : OL
1-3: 0.554 V
2-3: 0.374 V
2-1: OL
3-1: OL
3-2: OL

Diode D5001:
Pin (-,+) | Reading
1-2 : 0.374 V
2-1: OL

FET Q5000:
Pin (-,+) | Reading
1-2 : OL
1-3: 0.555 V
2-3: 0.423 V
2-1: OL
3-1: OL
3-2: OL

FET Q5036:
Pin (-,+) | Reading
1-2 : OL
1-3: 0.606 V
2-3: 0.399 V
2-1: OL
3-1: OL
3-2: OL

Diode D5119:
Pin (-,+) | Reading
1-2 : 0.399 V
2-1: OL

After those tests, I attempted to test the Y-Buffer board to find possible shorts from the Y-Main inputs to the Y-Buffer IC outputs. None of the video tutorials for buffer board tests matched the model of my Y-Buffer board, but I was able to find a bunch of pins on the connectors that were tied together on the input side of the IC's, so I assume any of those pins were viable for testing, based on advice from popular YouTube videos. Using the probe "sweep" test on both sides of the output connectors, I saw no issues, so I assume the Y-Buffer board IC's are free from shorts (although it's possible I was using the wrong pin on the input side for testing).

At a loss as to what to examine next. I will probably pull the SMPS board and try to test the FET's and diodes in-circuit to see if anything raises a red flag, but any additional advice would certainly be welcomed.

Thanks again for all of the help already provided!
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Old 04-28-2020, 11:03 AM   #14
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Default Re: Samsung PN43E440A2F – display turns off after several minutes

You don't appear to have a short circuit with any of the components tested above.
I would check your power supply especially looking for any grey solder joints and touch those up. My thoughts are that you may be losing the VS_On signal from the logic board.

Look at post #7 in the following post
https://www.badcaps.net/forum/showth...ghlight=vs_con

Last edited by dick_barton; 04-28-2020 at 11:44 AM..
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Old 04-28-2020, 01:06 PM   #15
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Default Re: Samsung PN43E440A2F – display turns off after several minutes

Quote:
Disconnect all connectors from the PSU, leaving the ac 120v in connector alone in place. Put two 120Vac household incandescent light bulbs in series and connect it across the Vs and GND pins on the connector that would have gone to the Y-sus Bd. Jump the VS-ON to the STDBY pins. Jump the PS-ON to GND. connect the 120Vac. If the PSU is good the light bulbs should light up bright and constant. Measure Va, D15 and D5.3, they should be spot on.
I just made myself a 240V bulb by stringing two incandesents in series. I disconnected all connectors from the PSU, placed the bulbs in series across VS & GND pins, Jumped VS-ON to STDBY, and jumped PS-ON to GND.

Once I applied 120VAC, the light bulbs lit right up and continue to remain lit. I measured the following pins while the bulbs were lit:
CN804:
D15V: 14.60 V
D5.3V: 5.26 V
VA: 58.5 V

It has been running for over 10 minutes now, which is much longer than I've managed to keep the display on thus far.

Thanks for the assistance @dick_barton. Any suggestions as to what to look at next? I take it that this means that the PSU is most likely not the issue here - is that an accurate assumption?

I looked for cold solder joints on the underside of the PSU, and nothing in particular caught my attention.
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File Type: jpg 20200428_145254.jpg (570.4 KB, 4 views)

Last edited by heathloder; 04-28-2020 at 01:55 PM.. Reason: Removed photo of incorrect board
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Old 04-28-2020, 01:31 PM   #16
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Default Re: Samsung PN43E440A2F – display turns off after several minutes

It certainly looks as though the power supply is not the culprit and so can eliminate it as a possible problem.
You didn't say what Vs voltage was. Just to make sure it's not rising above it's nominated value.

There are some other measurements you could make Ve, Vsc which I think are on the Ysus board. You could be losing one of those supplies.

Last edited by dick_barton; 04-28-2020 at 01:33 PM..
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Old 04-28-2020, 01:41 PM   #17
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Default Re: Samsung PN43E440A2F – display turns off after several minutes

Sorry about that!

Just measuered VS on CN804 while the bulbs were lit and it read 215.5 V, and the rated VS for this panel is 209 V (based on the sticker in the center of the panel on the back), so that looks OK to me.

I'm going to re-connect the other boards and see if I can get measurements from the Ve and Vsc test points on the X/Y-Main board. I only see one adjustment "screw" on the X/Y-Main, so I assume that's for Vsc (it's not labelled well).

I'll post back with those readings shortly.
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Old 04-28-2020, 02:28 PM   #18
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Default Re: Samsung PN43E440A2F – display turns off after several minutes

I just checked Ve and Vsc on the X/Y-Main, and here's the readings:
Ve: 98.4 V
Vsc: -185.6 V

The sticker on my panel makes no mention of Ve, so I'm not sure what it's supposed to be, but the value for Vsc is spot on (expected -185 V). Both of these reading were when the panel was 'ON'/displaying.

Also, just out of curiosity, is it correct to say that none of the FET leg's should show continuity to GND? I found this YouTube video (which has nothing to do with my TV, but does seem to apply to many plasma TVs in general): https://youtu.be/aZF57Bok7Ws?t=228 where at about 03:50, he mentions checking for continuity between FET legs and GND. I tried this, and found one FET on the power board that shows continuity between both of it's "outer" legs and the chassis GND. Should I remove this FET and check it again, or is there nothing necessarily strange about this scenario?
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Old 04-28-2020, 03:22 PM   #19
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Default Re: Samsung PN43E440A2F – display turns off after several minutes

I wouldn't worry about the checking to ground. He had a blown fuse which is generally caused by a component going short circuit, nomally it's the mosfets which often have a path to ground.
In your case everything appears to function correctly for the first 5 mins or so therefore not indicative of any short circuit problems.

What you could do is use a hair drier and warm up your boards to see if you can shorten the time the set runs for. If the set switches off sooner then you could narrow down the area you are heating until you find the most sensitive spot.

Other than that I don't know what else to suggest so maybe someone else with more experience could make a suggestion.
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Old 04-28-2020, 08:25 PM   #20
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Default Re: Samsung PN43E440A2F – display turns off after several minutes

Okay, so after hours of scouring the web and trying things out, I think I've finally made some progress. If I followed your hair dryer tip earlier, I would have saved myself hours... On the bright side, I'm pretty positive my Y-Buffer and X/Y Main boards are in pretty good shape after all the time I've put into testing them (and seeing them at work when the display does power on).

Long story short, I can keep the display on by keeping my thumb on the "primary" BGA IC on the Logic Board (circled in red in the attached photo). I can also basically "force" the display off by heating that IC for just several seconds with a heatgun. Once the IC is at a specifiic (relatively low, actually) temperature, the unit will keep booting into the error state I kept experiencing if I try to restart the TV. I can get the display back on normally again within seconds by just getting the IC temp down to a little above room temperature.

I really appreciate all the assistance with this. Since I don't have anything to lose, I plan to try a very basic re-flow using a heatgun (and cover the surrounding areas with foil tape), like the gentleman in this video: https://youtu.be/C-abHE6sq8U?t=1737. If that fails, I'll purchase a replacement Logic Board. Before I potentially sacrifice this Logic Board in the name of learning, does anyone see any reason that attempting to re-flow this would be bad idea, or have any advice about this in general?

I will post back with my final results, just to confirm that this was indeed, the only issue.
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