My buddy's Dell 50" W5001C plasma television conked out one day so I set out trying to fix it. The TV is about 4 years old, and it is out of warranty. Even the three year extended warranty that was offered for $1000 at the time of purchase would have done no good. (Remember when TV's used to last 20 years?) With no recourse for repair through official channels, what is one to do?
"So what are my options?"
1.Fix it at a TV repair shop
Calls to television repair shops produced a range of estimates, i.e. $300 for an on-site consultation and no guarantee of repair. Shipping or transporting the TV to a repair shop could could add insult to injury as it is quite large and might be damaged even further during shipping.
2.Buy a new TV
With new plasma TVs costing about $1000+ for a similar model, it's a tough call between getting the old one fixed or just purchasing a new one. If repairs are more than $500, you'd be better off just chucking the old one and buying new. Since the Dell wasn't smoking or on fire and looked like it was still in very good condition, throwing it away seemed like a waste.
3.Take it apart
While my buddy contemplated what he wanted to do (see options 1 and 2 above), I resolved to just take the dang thing apart to see what I could see. I'm fairly electronics savvy and I love taking things apart, so this was an opportunity not to be missed.
The Bottom Line
Long story short, a $1.09 part took down a $4000 television.
The information contained herein is only a journal of my experiences. It is not meant as a tutorial for someone else to fix their own TV. If you use it as such, you do so at your own risk. Don't blame me if you destroy your TV or get hurt in the process. With that said, please continue reading....
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Step 1: Symptoms
1. Blank screen
2. TV still powers up, blue led lights up, and relays click at turn on
3. Sound still works
4. Picture may come back for hours at a time but not reliably
5. Picture may appear for a split second when turning off.
How it happened
It all started one day when I went to turn on the TV and, while the power LED lit up and the power relays clicked as usual, the screen was blank. I thought it was on the wrong input so I used the controller to switch inputs but the on-screen menu would not show up either. The sound, however, was working so it was definitely on the right input already. I left the TV on for a while and after a couple minutes, the picture magically appeared! Great, it just needed to warm up I thought. After being left on for a couple of hours however, the screen went dark again. The TV was basically unusable because turning on the TV would usually result in just a dark, blank screen. Since the sound continued to work, I suspected something to do with the power supplied to the plasma screen proper.
Step 2: Teardown
To access the power supply, one must remove the sheet metal backing to the television. This is quite easy and only requires a T20 torx screwdriver and a common philips screwdriver. There are many torx screws around the periphery, four large philips mounting screws, and a couple smaller philips screws. Once all screws are removed, the sheetmetal backing can be pried off the TV (in fact, it may fall right off after the last screw is undone so watch out!) It helps to have a friend at this point because handling the large back piece can be a bit unwieldy with one person..
Step 3: Testing the Power Supply
Static Electricity Warning
Some components on the power supply are CMOS integrated circuits and are therefore sensitive to static electricity. Before touching the circuit board, I make sure the TV is unplugged. Then, I touch a piece of metal on the back of the TV that is grounded, i.e. part of the metal frame or one of the mounting screws or mounting posts of the power supply board. This will dissipate any stored static electricity by the body and discharge it to ground. CAREFUL!!! This should only be done with the TV turned off and NOT plugged in. Otherwise, one might touch something with HIGH VOLTAGE and receive an electrical shock. In particular, stay away from the large heat sinks with the yellow stickers on them indicating high voltage.
The power supply is the large circuit board in the middle of the TV. It has many transformers, large capacitors, and a couple IC's. There are eight connectors attaching the power supply to the other circuit boards on the TV. Looking closer, one can see that the power supply(Model#:PSPF651B01A) is manufactured by Samsung, as is the plasma screen itself. The supply provides about ten different voltages; 190V, -180V, 60V, etc for the plasma screen as well as 3.3V, 5V, and 12V for the logic and digital electronics.
The power supply circuit board contains a wealth of information including its part number and a table of the different voltages it produces along their signal names(Va, Vscan, Vstb, etc). Test points for all these voltages exist on the left side of the board(looking at the power supply as it is mounted to the back of the television).
How to test
I used a multimeter to probe the voltages at the testpoints with the TV turned on. BE CAREFUL!!!! This is of course highly dangerous as HIGH VOLTAGES occur on the power supply and the TV was not meant to be run with the back off. Touching certain points on the power supply while it is powered can KILL YOU!!!! To be safe, don't touch ANYTHING inside the TV whilst it is plugged in. In fact, if you do not know what you are doing, just stop here. No point killing yourself over a stupid TV.
If you dare....
The RTN node (seen on the silkscreen at the top left connector(and others) ) is basically the common grounding point and is connected to Earth ground, the shiny metal backing of the plasma screen, and all the metal mounting pegs that the power supply is mounted to. The black or negative lead of your multimeter should be attached to this point. I just stuck the black probe into one of the mounting studs and let it hang there (out of the way) so I could probe using the other(red) lead of the multimeter with one hand.
Start off with the TV unplugged and turned off. Attach the negative or black lead of the multimeter to any mounting stud near the power supply board. Now plug in the TV and make sure nothing explodes. Now turn on the TV with the remote control and again make sure nothing explodes. Is the screen blank? If so, good. You'll be able to probe the test points on the power supply to determine which voltage is not being produced. In my case, it was Va which is supposed to be 60V. Make sure to make a good contact between the testpoint and the multimeter probe. If the contact is poor, the voltage readout may look as though it is fluctuating between the spec'd voltage and some lower voltage. For example, if the spec'd voltage is 180v, not pressing hard enough to connect the probe and the testpoint may result in a readout that wanders between 180v and 50v.
If all the voltages are being supplied and withing spec (as shown on the power supply's silkscreened voltage table shown in the fourth picture below), your power supply is most likely functioning correctly. Your problem may lie in a different area. Numerous people have mentioned a problem with their Y-Buffer, the circuit boards flanking the left and right sides of the plasma screen. Specifically, whitby905 (see the comments section) has found that the lower left Y-Buffer board was contacting the metal plasma screen backing and had shorted out. If your power supply checks out, look and smell for any indication that any of the Y-Buffers have shorted to the case. You may have to remove them and look on the back for shorted solder points. I don't have any pictures of this situation besides the one from whitby905 in the comments section.
My problem was with the Va voltage of the power supply so I will continue discussing it in the next section "Debugging on the Bench."
Step 4: Debugging on the Bench
More testing in the lab revealed that the problem was a defective IC, U501 which is a Fairchild Semiconductor part KA3883. I ordered a replacement from digikey, 497-3678-ND, which is a STMicroelectronics UC2843B, for $1.09. The original KA3883 is not generally available(discontinued?). UC2843B is a higher quality drop-in replacement.
The proof that the current mode pwm control chip(KA3883) was the source of the problem came from heating just that part with a hot air pencil and watching the Va voltage go up to 60V then cooling the control chip(KA3883) with a can of compressed air and watching Va go back to zero. The part is defective and for whatever reason responds to thermal shock. This could have indicated a cold solder joint but, after checking, the solder joints looked fine. Diagnosis: defective KA3883.
The power supply board is easily detached by removing about ten philips screws and disconnecting the eight connectors.
If you want to test the board on the bench, away from the rest of the TV), you must use an isolation transformer. Plug in one side of the isolation transformer to the wall then plug in the board to a suicide cord connected to the other side of the transformer. This is so you don't die.
You also need to know how to turn on the board without the remote control, right? This is done by simply connecting pin 'PS-ON' (found on connector CN8007) to ground(ie the RTN pin). I used a small jumper to short across from PS-ON to RTN. You can just leave the jumper there and use a power strip to turn the whole thing on and off.
I traced out much of the relevent circuitry to make sure I knew what I was probing and so I could debug the Va circuit. The excellent layout and silkscreen notation on the Samsung board was very helpful. The Va circuit is mostly contained within the 500's numbered parts, ie U501, C501, R501, etc. If you are going to probe any of these parts with the board powered you MUST USE AN ISOLATION TRANSFORMER so you don't electrocute yourself or destroy the board, especially if you are using an oscilloscope or something that is not battery powered.
Step 5: Replacing the Controller Chip
The first thing you need to do is get rid of the defective part, U501.
One method is to remove the chip by getting rid of the solder holding it in place. Either use a solder sucker desoldering station (if you have access to one) or solder wick to remove the solder then pull the whole chip out. Careful with the solder wick. If you heat up a pad too much, you WILL lift a trace, effectively destroying the board. It's very hard so get it right with the solder wick.
I used the desoldering station to clear the lead holes. Then, I attached the SIP sockets to the new part, placed it into position, tacked the part by soldering pins 1 and 8 to hold it into place, and then soldered the rest of the pins. The reason for using the SIP sockets and not a normal 8 pin socket is because the width of the holes is unusual. DIP parts are normally 300mils wide however the width used on this board for the DIP parts is about 340mils (when I say width I mean from say the center of the hole of pin 1 to the center of the hole of pin 8.) A normal 8 pin DIP socket will not fit, hence using two strips of SIPs. However, mhra08a has used Radio Shack 8-Pin IC Retention Contact ($0.48 Model: 276-1995 Catalog #: 276-1995) with success.
Better Method(if you don't have a desoldering station)
I suggest just cutting the leads off the old part and soldering in a strip of 0.100" pitch SIP sockets to the old leads that are left sticking up out of the board, ie a strip of 4 on one side and another strip of 4 on the other. Try digikey ED7064. This way, there is no desoldering and you'll have a socket there to make it easier if you have to replace the part again. You must be very careful when using a small side cutter to snip the leads from the chip (this is the simplest way to do it however). The action of the cutter will push the lead and the chip to the side, putting lots of stress on the hole that the lead is soldered into. Again, damage of the circuit board could result.
Also note jackohound's method he describes in the comments section:
"As I didn't have a desoldering station, or a small enough side cutter snip the U501 leads, to I used a Dremel tool with a very small cutting disk to carefully cut teach of the leads from the old chip. This required a steady hand, but it avoided putting any stress on the board. I removed the old chip body and used a handheld spring-loaded desolderer to remove solder from each of the holes."
After the chip body is removed, you can solder the SIP sockets to them. Watch out because when you touch the soldering iron to the lead you will also melt the solder in the lead hole and the lead may move, fall through, or cock to one side. You might try first soldering a solid wire to all four leads on one side to keep them in position as you solder the SIP sockets.
Make sure you install the new part with the right orientation! Otherwise you'll probably blow a fuse on the board(best case) and may take out some other parts as well.
Step 6: Conclusion
Now install the board back onto the TV, and connect only the smaller connectors to test the board. Plug in the power to the TV and turn it on with the remote. Probe the Va testpoint with a multimeter to see if it is between 55 and 75 volts. If so, the repair worked! Turn off the TV, unplug it, and install the other connectors to the power supply board. Install the backing onto the TV and you're done. Congratulations! Your roommates now think you're a genius.