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2015-12-08

Samsung Plasma PS51D6900 - not starting - smoked DC-DC converter BD9153MUV on logic board - Panel defect - address buffers kill logic board

This is a long story with no happy ending, but many interesting findings.

This pretty Samsung plasma machine caught my eyes on eBay classified. The reviews were very good at the time. It almost matched the image quality of the Panasonic GT30, which I have and love. I always wanted to take a look into a Samsung plasma, so I got it for a fair price. From the outside it was in mint condition. Not a scratch.

The device would click once plugged in and the stand-by LED blinked six times. Then silence. Just a slight buzz from a transformer in the SMPS.

I browsed the net for the six blinks, and apparently this doesn't mean anything. It's the normal startup blinking. As always, this Samsung had no proper self diagnose error codes. Suckers.

First, I had to extend my "lab" table to make room for the monster.


It is chock full of boards, no comparison to an LCD TV of the same size! Plasma screens require hardware.


No bloated capacitors. Standby voltage and all other voltages to the main board where all ok, the processors were warm, no findings on the regulators. PS-ON signal was low, which means "start". However, the power supply did not start any of the voltages for the scan/sustain boards.

I browsed the net and found this very useful instruction movie from Samsung, which goes through a number of power up sequence checks:

I stopped at the VS-ON check. This voltage was supposed to go high from the logic board. It didn't.

So, up next: logic board check. Fuse ok, but no voltages at the switching inductors. Upon closer inspection it was obvious why. The DC-DC converter was smoked. 


And a look through my 10x magnifier showed damaged traces, too. The chip is a BD9153MUV step-down converter. 



This board was toast. No point in soldering a new converter. Also, I had no clue why it burned up, maybe some chip had a short and killed it  - not likely though, those converters normally have protection circuitry. The chip was shorted on both switching output lines (S1, S2)

The good thing about Samsung TVs is that spare parts are available in numbers and cheap. A shop in Great Britain offered one for 25€ including shipping and a 30 day return policy. Deal!

Well, after I had mounted the new board, the TV seemingly booted. The logic board was blinking once per second, as explained in the video. Vs and Va voltages were ok. The converter chip was not getting hot and produced 3.3V and 1.18V. So that was looking good.

However, still no image.

I switched it on and off a few times and one time I lifted the set up from the table, to check if the menu would come up - dzzzzt, smoke, the chip burned up again! Argh! WTF? This time, only the S1 output line was shorted and no traces melted.

Time was too short to try the logic board self test screen patterns, which run without the mother board. This would tell me whether the panel, sustain, and logic boards work together properly.

So now what? What was killing this chip, why did it take a couple of minutes, and why wasn't it getting hot when I checked?

I removed the chip from the original board and checked for shorts on the output lines. None! All in the safe 10k+ Ohms range. This is really strange. Has the chip destroyed itself?

I ordered 10pcs via Aliexpress and replaced the DC-DC chip on the second board. That took hours and many failed attempts. Those tiny flat pack chips are a nightmare to solder, because the pins are flat underneath the package, unlike normal ICs where they stand out.

Just look at that tiny bugger:


Positioning it tested my patience. Hot air attached the chip on the pad, but the pins just wouldn't pick up the solder, most likely because I had too much solder on the pad and the pins did not reach down enough. I had to use the iron. Unless each pin has a shiny solder blob on it, the thing will not work. I think the art is to apply just enough solder on the traces and pad, and then reflow the damned thing until it sinks in. Or maybe: fix the chip on the pad first, then apply paste to the edges and then reflow. I think I'll try that next time.

Back in the TV the chip produced 1.2V  and 3.3V and the heartbeat LED morsed the OK code. Still no image.

Ok, logic board self test! As described in the video, first jump-start the power supply by shorting PWR-ON to ground:




Then, put a jumper on the upper two pins of the test jig:


After plugging in, the TV should start itself and display various test patterns.

Nothing on the screen. However, I noticed an alternating buzz from the scan boards. The logic board was producing something and the scan machinery did its job. Thus, the processor on the logic board was able to run a program. Could I conclude that it is 100% ok?

The following possibilities were left:
0) The processor is partially dead on its output circuitry.
1) Some shorted address buffer is pulling everything down.
2) None of the address buffers are working.
3) The software on the logic board doesn't match the panel.
4) The panel is generally FOOBAR.

Check 0)
How would I know? The processor runs its self test alright.

Check 4)
Can't do :-(

Check 1)
The address buffers have three connectors to the logic board. They are independent. When you disconnect one buffer board, the other half of the screen should still be ok. I checked one connector after another and got no picture.

Check 2)
I removed the cover from the address buffers to take a look.


There is a fuse for the Va voltage. It checked good and Va had its specified value.


I fired up the TV and checked if any of the driver chips in the flat cables, which connect the panel, get hot. Nope.

It is not likely that the address buffers are the problem. Cover back on.

Check 3)

There seem to be a number of versions for this board. While browsing eBay, I noticed a variety of labels on the U2002 SDRAM chip. It suspect this documents the software on the board, which is stored in the Flash memory chip U2012. The flash chip is too small to put labels on.

The label on the original board:


The label on the second board: 

It is also possible that there was another sticker on top of this one and it got lost. I think the first line is critical. I found the DS/DE label printed on the address boards, so that seems to match the 51'DS. Does FF really fit?

What now? Swap the FLASH ROM chip!
Done. Even louder buzzing from the scan boards. Still no image.

Swap the EEPROM U2007!
Done. No image.

Fuck this. Found another board on eBay with the exact same label and ordered it. If that's not going to help, we have case 4: FOOBAR panel.

So, the second board arrived quickly. Plugged in. No difference. I measured all voltages again and VA was not stable. It started with 58V and intermittently jumped up to 74V during the self-test. This can not be good! The problem search closed down on the address buffers.

Then I lifted the screen a little and found some dancing red pixels on the bottom edge. To get a better look I put the TV in a vertical position. Suddenly it switched off and the power supply would not restart (click, click, click). I replugged the power line - pffffft - DC DC chip blown again.

Cross check with the repaired board and the TV laid flat: same red pixels, which I did not notice last time.

This TV was susceptible to gravity! Once it stood vertically, it apparently kills the logic board via its address buffers. Crap! The only reason left was the panel. Major bummer!

Before I finally dismantled the whole device I ran a last check on the VA voltage. I unplugged the VA power supply connector to the address buffers, ran the self test and measured. At the power supply, the 58V were now stable. However, on the buffers, there was a voltage! It seemed that scan or sustain voltage was creeping into the address lines and from there into the buffers, the logic board, and the power supply. Some internal isolation in the panel must have been broken. That's why the power supply refused to start in vertical position. The voltage was far off and the overvoltage protection jumped in. The poor logic board had no defenses and died.

It think it is very unusual for a panel to fail completely. Normally at least some parts are still working and only a few address buffers or sectors are dead. Here though, the whole image was reduced to some red pixels noise on the bottom.

This was an expensive, yet educating experiment. I now own a large piece of junk. At least the scan, sustain and main boards are ok for sure and can be sold.


13 comments:

  1. Hallo Hermann,

    hast du noch Erfahrungen sammeln können, die mir helfen könnten, meinen PS51D7000 mit selbem Schadensbild auf dem LogicBoard wieder beleben zu können?
    Einen DisplayFehler kann ich fast ausschließen, irgendwoher muss die Überspannung aber ja gekommen sein ...
    Siehst du Möglichkeiten, die individuelle Software auch "soft" auf eine andere Hardware zu bekommen? Habe ein Hardware-identisches Board gekauft, aber ist anders gelabelt und deswegen wohl unbrauchbar ...

    Merci für Tips!
    Stefan
    Steff at NeuroticShark.de

    ReplyDelete
    Replies
    1. Servus,
      also wenn das Logic Board nicht abgebrannt ist, dann wäre die beste Reparatur, den dc dc Converter zu tauschen. Ohne die passenden Geräte (Eeprom programmer) bringst du die Software nicht von A nach B. Ich weiß nicht, was die Labels genau bedeuten und was kompatibel ist. Ich würde aber annehmen, dass beim gleichen Fehlerbild auch der gleiche Fehler vorliegt. Dem Panel wird es nichts ausmachen, wenn das Logic Board nicht genau passt, es kommt halt evtl. Blödsinn raus. Ich empfehle dir aber dringend, die Va Spannung genau zu untersuchen, ob sie stabil ist oder rumeiert wie ich beschrieben habe. Dann ist das Panel leider Toast.

      Delete
  2. Hello Hermann.
    Maybe You can help me. I have no oryginal power cord for this model.
    Do You know description of this connection?
    https://spares2repair.co.uk/bmz_cache/4/446f8007b7348ed6c767f54fd7c3b800.image.600x511.jpg
    Thank You

    ReplyDelete
    Replies
    1. Hi Rafal,

      I'm sorry, I don't have any information about the cable, either.

      Delete
    2. Maybe You Have better quality od 2nd photo. It should be described on part where N L and Ground should be connected. ThanK You

      Delete
  3. Did you click on the image? It gets pretty big. Ground is in the center, that's the important info. L on top, N on the bottom. N/L is irrelevant anyway because you can turn the mains plug in the socket and they get reversed.

    ReplyDelete
  4. It works. Thank You Hermann. My plasma alive.

    ReplyDelete
  5. Hello !
    I recently got a samsung PS42c96HDX plasma TV for free. I'm trying to revive it.
    Reading your stories in your blog Samsung plasma seemed to be creepy stuff...
    It didn't want to power on. SMTP had bulged capacitors so I replaced them. I checked the output voltages and I got the right values.
    On power on, I got a blue led back but no start up.
    Relays cliks once or twice when plugged, another clik switching the central button and ...no samsung start up sound.

    I can see some reactions on the panel but no image. I can hear buzzing both Xmain and Ymain cards.

    I can see the logic board led blinking so I assume it is ok ( visualy nothing seems burnt )
    The main board's processors are hot.
    The only part that is not hot is the X-board and I'll check the voltages later.
    Could it be that part that stops the tv start up ? If I disconnect the X board it doesn't change anything to my problem.

    Thank you again for advices

    ReplyDelete
  6. Hello,
    I recently got a Samsung Plasma TV PS-42c96HDX for free.
    I fixed the smtp board which had bad capacitors at the bottom right part .
    I checked voltages outputs and everything seems to be ok. when I switch on the the TV I have Vs / Va / Vamp 18v / Vg / 12v / DC 5.3V / STD 5V as expected.

    The logic board led is blinking and I can see the red light from the optic source on the main board.
    The main board processors are hot.

    But there is no start up sound and a very fade image backlight seems to flicker a little.

    At this point, I could think I got a problem with X Board or Y Board but would it prevent the tv from starting correctly ?

    I followed the service manual instructions and I disconnected X board, Y board and Logic board from STPM but TV did not started.

    Reconnecting each board one by one didn't make it too.

    Any Idea, please ?
    Thank you !

    ReplyDelete
  7. Hi, I am not familiar with that particular device. Have you tried the logic board self test?

    ReplyDelete
    Replies
    1. Hello, sorry I did not tried. Have you explained it yet ? I'll search the web and your blog for it.
      thank you

      Delete
    2. Ok so I was prety sure to have read something about self test logic board. I've yet identified the 4 pins on the logic board. Let's try it when I get back home.

      Delete
  8. Hi and thanks for sharing your story. Really enjoyed reading :-)
    Exact same TV model here and EXACTLY the same converter failed on Logic board due to thermal overstress. But after replacing and first hour of testing everything seems perfect again (picture is back, no heat, Va Vs Ve etc fine).

    ReplyDelete

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