Dell W5001C 50" plasma fix


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."
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