Tip & How-To about Televison & Video
You turn on your beautiful plasma or LCD flatscreen and you hear a click, the standby light goes green for an instant and then it goes to red, with another click and no more activity from the TV. You have a major problem with the unit, which unplugging it for a while is not going to solve. You probably have a short somewhere, but where?
I will try to help with the where part of the question.
If the unit runs more than several seconds chances are the power supply is not the problem. It could be, but I doubt it, even so I will explain how to determine if the power supply has a problem or not.
If you are good with tools, and observant, you should be able to fix this.
You will need a DMM and a few hand tools as well as a soldering iron. Of course good soldering skills are almost always necessary when fixing TVs.
You can get any meters or tools from http://www.mcmelectronics.com as well as any discreet parts you may need.
You will have to work on the unit live to test voltages so you will need to be very careful as you will be exposed to lethal voltages. When the back of a TV is removed lethal voltages are exposed.
If you believe that this is more than you want to tackle stop now. If you are going to proceed, unplug the unit. Remove the back cover by removing all the screws around the perimeter and any on the back proper. Sometimes it can be challenging finding them all. They are usually marked with an arrow pointing towards them.
Once the back is off look at all the small cans on the board at the top center of the back. This is the power supply and you want to see if any of the electrolytic capacitors are bad. Generally on these kinds of TVs if the electrolytics fail they rupture and will be swelled. They may have the top pushed up.
If you find any bad capacitors replace them with identical units. Pay attention to the polarity when you take them out. They have a positive and negative polarity and if put in backwards they will short out. The negative terminal is always marked on the board with a heavy dark line or dot.
Electrolytics have two parameters. Capacity in microfarads and voltage limit in volts dc. Replacements must have the same two values which are stamped on the side of the capacitor. You can use capacitors with a higher working voltage, and depending on the application a higher capacity, but if you do not know how they are being used, replace them with identical units.
Once you have replaced any bad capacitors test the TV. If it works you are done.
If it does not you will need to proceed with troubleshooting the boards.
The board to the left of the power supply is the YSUS board and is used to drive the screen. It works in conjunction with the Sustain board, on the right side of the back. The YSUS board is connected to the upper and lower drive boards (there may only be one on your set) and they are connected to the screen via ribbon cables. If the drive boards need removed to remove the YSUS board be very careful when moving the drive board not to damage any of the ribbon cables.
Both the YSUS and Sustain boards demand a lot of current and are prone to failure. Find the bundle of relatively large wires which go from the YSUS board to the power supply and the Sustain board to the power supply and disconnect them at the power supply board.
Look at both the YSUS and Sustain board for bad electrolytic capacitors, as previously with the power supply board, and replace any which are found. Test the unit for proper operation and you may be done.
If not, you will need to proceed with testing the power supply board for proper voltages.
During the test procedure never try to test the primary side. This will short out the unit because one side of the unit is hooked directly to the hot side of the AC circuit. The DMM will provide a direct path to ground and short the unit out.
You want to test the secondary side only. Both the primary and secondary should be marked, probably at the top of the power board. Generally the secondary side is to the left of the board as you look at the unit from the rear, but find the correct designation and stay on the secondary side only.
Now look at some of the smaller connectors on the power supply board. You should see that they will be marked with voltages (12vdc, 3.3 vdc, 15 vdc, etc) and perhaps Gnd (ground). This is where you will be doing your testing.
Once you have located the connectors with the voltages marked you have reached the dangerous part. During the next part of my instructions, if possible, keep one hand in your pocket to avoid shocking yourself.
If you are ready to perform the test, plug the unit in. Press the on switch. You should hear the turn on relay click and if the short is in the YSUS board or the Sustain board, both should be disconnected, the unit should run, albeit with no picture or sound.
Using the DMM on volts DC - 20 volts range (or autoranging if you bought one) check the various voltages on the power supply board at the secondary output connections. You should touch the black lead to the pin marked Gnd (or the frame of the set) and the red lead to the pin of the voltage to be measured. Check all the voltages being produced.
If all the voltages check ok you have a bad YSUS board or Sustain board. The most likely culprit would be the YSUS board. You can obtain one at the following sites http://www.encompass.com or http://www.shopjimmy.com .
If the board you purchase is not the problem you can return it, less a small restocking fee.
The board removal should be self explanatory. Remove all connectors and all hold down screws. Replace with the new board in reverse. If we were correct about the YSUS board you should have a working TV.
Thanks for using FixYa and for the great rating.
Posted by Kim... on
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