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:

Power Up Sequence Diagnose

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.

Panasonic Plasma TX-P42G30E - panel defect - black vertical bar - broken data driver - case study

I spotted this Panasonic on eBay classifieds for little money in my hometown and there was no reason not to buy it, even though I suspected by the looks of the photo that it was a panel failure. I could sell the boards on eBay in case my remote diagnose was right.

Let's have a look:



The vertical black bar is the characteristic symptom of a dead data driver. It can't be the scan board, because the left side is ok. But why is almost half of the screen dead?

The data drivers, which are part of the panel, are connected to the C1 and C2 boards. The C1 supplies the right side with 7 drivers, the C2 the left side with 8 drivers. That's why the image failure does not cover exactly half of the screen as you can see in the next image. It is half minus one vertical driver bar.



Could this be a C1 board failure or is the broken driver pulling the whole side down? Let's verify. To access the connectors, a few things had to be removed. Then I pulled out the connector to the broken driver.



And look at that, the other 6 came back alive!



So this settles the case. The panel is dead. To be 100% sure, I plugged the dead driver back in. Yup, there were ghosts of the previous image and the current image wouldn't appear.



Unfortunately, my plan B, which was to use the boards as spare part donors for my other two Panasonic plasmas (in case they break again), proved to be wrong. To my surprise, this one is not built fully with SMD parts, it still has through-hole semiconductors. I did not expect that, because it was produced in the same year as my P42ST30E, and I assumed they would have similar chassis.

Philips 22PFL-3606H/12 - Not starting - defect TPS54319 DC-DC converter U702 on main board

Baby TVs also can go kaputt. I got this little 22 inch sucker in a package together with a bigger one. It wouldn't start. A service manual was readily available at elektrotanya and I was looking forward to solving this case.

Just look at the little one! :-)

Standby voltage was ok. So I focused on the mainboard's DC-DC converters. They all measured ok. Was this probably a CPU or EEPROM problem? Hard to tell and not fixable for me.

I then remembered a YouTube video from the infamous EEVBlog, where Dave fiddled with a processor stuck in reset mode. So, just for fun, I located the reset pin at the CPU and put the multi-meter probe against it. The capacity of the meter was enough to pull the pin low for long enough to make the TV reboot. And lo and behold, something happened and the backlight turned on. Sometimes. Most of the time nothing worked. Once the set even booted fully, but didn't stay up long.

Suddenly, I heard a buzzing noise. The 3.3V provided by the main DC-DC converter chip U702 was wildly oscillating. It stopped freaking around when I pressed my finger on the chip, and the TV booted once I reset the CPU! So, this regulator did not provide a stable enough voltage during the boot process. Afterwards it looked as if everything was ok. Obscure failure that one.

Ok, I ordered 5 pieces of the TPS54319 chip from a seller on Aliexpress.com. Those QFN16 package chips are tiny and very difficult to solder. I fried the first one and it took three attempts until the thing sat aligned with the solder pads. Would you believe that this breadcrumb is capable of 3A output current? I find that quite astonishing.

The TV worked! It has a surprisingly good image, once the PC mode is selected and all the silly image enhancers are bypassed. Frau Johansson radiated into the room as good as it gets.

Philips 37PFL8694H/12 - picture solarized - another AS15F chip defect on TCON board

Have I already said that repairing AS15F chip defects is becoming a routine? This is my third repair of this type.

I like the higher Philips models. They usually have a nice image and proper sound. This one came in with a solarized picture, which seems to be the standard failure on 2008/2009 models. Some colors were off. Not as bad as the last one I fixed, but unmistakably, this was a defect AS15 chip on the TCON board. I have those chips on stock, so this was going to be some solder work with a very good chance of success.

Apart from the image defect, this set was in mint condition. Not one scratch.

The panel and TCON has been manufactured by AU Optronics (AUO).

Wires flopping in the breeze everywhere. Oh my.

First I was happy to see the TCON board not buried under the mounting bracket for the stand, but this was even more silly. The plastic frame, which goes all around the device covered it up:

Hidden screws :-(

With some screws removed and careful bending I managed to remove the cover to gain access to the gamma voltage test points. This would give me the final confirmation of the defect.

I was right. A couple of voltages were inconsistent. They must continuously increase from left to right. This board had a number of jumps in the voltages. No total failures, just half a volt off. This was consistent with the screen symptoms.

Ok, chip removed, solder pads cleaned. I prefer to use solder paste for the bottom pad. It makes the chip stick nicely to the board, and soldering the pins is easier. I first soldered the pins with the iron and then reflowed the whole chip with hot air.

This heat conducting block cannot be reused.

I had no 6mm material at hand, so I stacked a 1.5mm on a 5mm. I carefully had to position it under the cover because it would stick immediately and move out of its place.

TCON back in the TV. All good. Frau Johansson looked content, albeit a little tense, and I am happy about the successful repair.

This TV is a good one. I generally prefer the image of a CCFL panel over the LED types. The panel has no backlight bleeding and is perfectly even lit. The colors are natural and precise. There is a white balance adjustment available, albeit no expert mode. Sound is more powerful than average.

Philips 42pf9966 Plasma 2004 model - defect 100µ capacitor in standby power supply.

A little mouse can demobilize an elephant.

A friend presented a 2004 Philips plasma TV to me. The device would begin booting but once the relais clicked it switched itself off.

This is a BIG machine. Enormously heavy. The level of component integration just wasn't as high as today. Many boards with discrete circuits around. Even DC-DC converters, which come in chips today, were built with transistors.

It already has Ambilight - implemented with CCFL tubes, not with LEDs like modern models! Amazing.

It once cost 4500€ - not for very long though.

It had no stand and I didn't want to carry this monster into my lab, so I did some checks on it at my friend's place. Something had to be wrong with the power supply. It did not start all the voltages and switched off after 5sec or so.

I decided to pull out the supply for measuring in my lab. The excellent service manual was easy to find at elektrotanya. Wow, this is the biggest power supply I've ever seen!

I tried to figure out how to start it. In modern supplies this would be a simple connection to the power-good pin from STDBY or ground. Not here. This one produces three different standby voltages, which are partially looped through the main board and come back as OK-signals to the supply. It has multiple stages, which activate in a certain sequence controlled by individual signals.

I gave up on that and started to measure all the standby voltages instead. 3.3V, 5.2V were ok. But the supposed 9V were only 6.1V! I tracked down the smoothing cap. It was just a little 100µF SMD type.

I checked the voltage with my scope and the problem was clear: a 6V baseline and way too high spikes up to 9V. This cap wasn't doing its job. I removed it and it measured only 85µF. Dead alright! I soldered in a new one quickly and the voltage measured proper 9.5V.

Board back in the TV and it started just fine. Nice. As little as 1€ material bill this time.

This little sucker made all the difference in this enormously complex machine:

Philips used to be top of the notch. This plasma monster proves it. It is an engineering masterpiece, which flawlessly ran for over 10 years. These days Philips TVs don't stand out from the crowd. They are not even built by Philips anymore.

Samsung UE40C8790 - defect STD452S MOS-FET in Power Supply

I once had sworn not to test my luck on Samsungs anymore because you have to navigate the boards without proper service manuals. However, this set looked very interesting and its price was ok, too. A defect C-Series does not appear on eBay often. It seems to be generally reliable. On the other hand, there is a D-Series model listed almost every week and they usually have panel failures. Those are really bad. Don't buy a Samsung D!

This TV showed some reaction with its stand-by light, but wouldn't boot. It went click-click-click...

I have to hand it to Samsung, their higher models are looking pretty good:

It also has a fancier remote than the cheaper models.

Considering its young age - about 4y - I did not expect to find any dead capacitors. The seller said that it had intermittent problems and one day it wouldn't start anymore.

In this model Samsung went to extremes to design the device as flat as possible. It is not much thicker than my thumb! The chips on the mainboard use the back cover as cooler. Instead of the normal, large capacitors, they planted nests of tiny ones in parallel. That's not bad in terms of reliability, my only hope is that nobody will have to replace those. Not so easy to find.

The downside is that all connectors besides HDMI and USB need adapters. Even for the aerial antenna. That particular adapter was missing. The original Samsung part is ridiculously expensive. Some shops charge 35€!

Stereo? Who cares! Both speakers share the same cabinet:

A quick measuring of the voltages revealed a dead 12V line. It was dead short and a FET was the culprit. It's the little one in the center next to the coil:

A little weird how they botched the thing onto the board, right across two jumper wires.

An older version of the power board's schematic shows a different 8-pin type.

The solder joints looked terrible. The thing was already wobbling:

So here we have the reason for the intermittent failures. Cold solder joints. They cause instability and probably sparking, which eventually killed the FET. It is a very exotic part, a SamHop STD452S. The data sheet calls it STD4525. Anyway, there was none available on eBay for a reasonable price. I found a Chinese specialist called transistormosfet.com. 3$ a piece and another 8$ shipping. A fair offer. I ordered six pieces. This worked well. After 15 days they arrived as registered mail. I'll keep this shop in mind.

In a forum, people reported the same symptoms. This seems to be a standard failure.

So, what can be done to make the thermal situation of the FET more stable? It is obviously running too hot. First I used leaded solder, which is more elastic than lead-free. Then I decided to use a heat conducting block to attach the FET to the back cover.

First, two little splashes of nail lacquer showed me if and where it is making contact:

I carved out the plastic and did another lacquer check:

So that was looking good. I had the device running without cover and the FET surprisingly didn't run very hot. Anyway, this should prolong its life.

Frau Johansson was very happy with the results:

This TV has a very good picture. It is evenly lit, sharp, with brilliant and bright colors and good contrast. Like all the LED TVs a bit too aggressive in the reds and generally a little artificial for my taste - but I am a plasma man anyhow.

The sound is not bad either. A little inhomogenous, but powerful thanks to the closed resonance cabinet and both speakers working together.

So here we go, one part replaced this time.

Panasonic Plasma TX-P42GT20E - massively damaged SC board TNPA5081

I got this nice 2010 Panasonic 3D plasma from eBay classifieds.

The seller reported that the device won't start and blink 10 times. I pulled the service manual from elekrotanya.com and looked it up:

Wow. That's a long list of possible failures! As the price was ok I dared to go for it.

The service manual is a delight. The best I have ever seen. Schematics and layout of all(!) boards are in zoom-able vector format. There are block diagrams, which give you a good overview of the main components. Very thorough diagnostic and miscellaneous service information. This is what you get from a manufacturer who does everything himself and not buy from others.

Back cover removed and the usual excellent Panasonic build quality shows:

The difference between this 2010 model and the 2011 Neo Plasma TX-P42ST30 I repaired earlier this year is significant. Everything is much bigger and clunkier. Even though the circuitry is probably very similar, the large semiconductors in this one are still through-hole as opposed to SMD in the later model. Cooling is passive with large heatsinks without fans.

So, my first check on a Plasma always goes to the SC board. But what's this?! A diode and transistor are missing! The cheeky seller did not tell me about that. Bastard. That was the reason for the 10 blinks in the first place, but what's the rest of the story? So I began measuring. I found those parts to be dead:
missing: D482, Q452
short: Q421, Q422, Q403, Q402, Q521
burnt, open or off-value: R421, R551, R522, R521

From that point on I did not bother investigating any deeper. After plowing through this thread in the Badcaps forum I realized that the SC board was severely damaged and a complete overhaul was the only option besides getting a used, working one. The board has the tendency to blow up again if not all of the dead parts are properly replaced.

The repair kit from GTV Watford in the UK, which is a very good source, costs 84€ including shipping and is a hell lot of work (27 parts). Luckily, I also found a board for 68€ from an Italian on eBay.

That board had one rub though. It was the AY type for the 50 inch 3D panel. I needed an AH type. What's the difference? See for yourself:

The only differences I found were the coils and the capacitors around them. The green and blue big drops and one electrolytic. A guy in a forum explained that this circuit is tuned in resonance with the individual panels to suppress electromagnetic emissions.

The board from Italy measured flawlessly. To be safe that none of the Y-buffers had killed the SC board, I removed all the panel connectors and measured the buffer outputs for shorts as well as the pins on the connectors to the SC board. No findings.

Now, to morph the AY into the AH type I swapped out the differing parts.

Board put back in and the TV worked. Almost. Because I removed the panel connectors, I had to go through the incredibly tedious routine of refitting them, which never works at the first attempt. The latches of the sockets on the buffer boards have the tendency to push the flat cables out of their position. Horizontal black lines and blocks all over the screen was the result. After 20min of trial and error everything was sitting were it should and Frau Johansson looking gorgeous as ever.

This older generation of Plasmas does not have the stunning image quality of the 2011+ Neo Plasmas. It is interesting that the image looks "analog", as if a CRT TV was pimped for HD. Nowhere as overly crispy digital and bright as modern LED LCDs are. It is pleasantly smooth and totally natural. This model also has an expert mode with countless image adjustments.

So, this adventure once again confirmed my impression: Panasonics are the best. Period.