Power Supply Replacing?

Bit of technical knowledge is must to do this task.Yes its not a hard tough job.
OK there is generally nothing "Special" about mains, wall power supplies, they simply provide DC volts, via a step down transformer, or switch mode technology, now there are ONLY three important things to know and they are, the Voltages, and Amperage, and Power Plug Polarity. 
You can often find this A: In the manual under Power Supply Specification, B:Or on the Actual power Supply itself, If one looks carefully, there is always on a UL listed power supply, the Output Voltage & Amperage, often Polarity is indicated too. If not, that can be inspected usually, by looking besides the power input socket, on the actual unit, and, it usually, has a little drawing, with a dot and a 3/4 circle around it, with a + & - showing what goes where. In almost all occasions, though, it is Positive to the CENTER, & Negative to OUTER, (or earth). All you have to do, is get any other power supply that has the SAME Voltage and Current rating, IE: 12 Volts @ 2.5 Amps. Now any 12 Volt supply that gives, the same or MORE than 2.5 Amps will do. You just need to ensure that the Plug is right, often the plugs are different, that too, can be overcome, simply, by cutting off the OLD, plug, and cutting off the NEW plug, and joining, Old, to New end on PSU. Again, usually, Positive is the Center, and the Negative is the Outer. Right go get that supply. Ebay or Radio Shack, are good places to start. Also any other "Laptop" power Supply that has same specs as described, will also work. As a matter of point, switch-mode is generally "Cleaner" power than a transformer one.But it is NOT critical. All laptop, and some other things, power supplies, have "Chips" in them, to "Help" with charging? that's what "they say" Sometimes, you cannot replace this type of power supply, with anything other than the exact replacement, BUT it is still worth a "try" it will/should not ruin anything all that may be compromised may be the "Charging" of the/any battery. That is why batteries can "Fail" and cannot be recharged, NOT due to the batteries actually being "Faulty" oh no, it is simply that the "Chip" has failed and that often, stops the battery from being "Seen" and/or recharged.


This details will help you to understand the basic theory.
Thanks.

TV repairing?

Repairing tv needs various components and diagrams.
Ok so you want to service your own TV, well i will briefly describe what you may need. First and foremost you need a Service Manual, why you may say? well if not for the troubleshooting algorithms, and component placement. The MOST IMPORTANT thing is that these manuals give us the PART NUMBER that identifies EVERY component and part in the TV. Without this number you simply cannot order parts, as there is no way to describe what you need, without it. 
You need a Good Multi Meter. 
You need an Isolating transformer if you do not want to kill yourself. 
You may like to make a pair of switchable out, 100 Watt light bulbs wired in series in the mains circuit, to "Buffer" the Voltage and so you can work on hic-upping switchmode power supplies. 
Ideally an Oscilloscope. at least 100MHz. Dual Input. & 1:1 & 1:10 Probes; 
Tools, include, Torx drivers, Philips screwdriver, Slot, Small Side Cutters. Long nose Pliers, Tweezers, Soldering Iron, 40 Watt fine Conical Tip. Solder, De-soldering Pump.. Various "Solder Picks". Small Dentists Mirror and Magnifying glass. 
Also a Dual Output Power Supply, proves invaluable. 
With the help of the above mentioned tool and service manual, you can repair your tv.
But basically you need to have voltage testing and soldering iron using knowledge.With you this knowledge it will be difficult for you to start troubleshooting.

Why electric units fail?

There are number of possibilities.
Testing,inspecting and troubleshooting is the only way to confirm what caused the unit to fail.
When a unit faults, it will always give a Symptom, now, the Symptom is what the user is experiencing, and a symptom, is exactly that, a Symptom. Now, just like with people, there can be many, many, things that can bring about the same set of symptoms, say like fever, a fever can have any number of "Causes" from the Flu, to say Bubonic Plague... Well, just like our bodies, electronics are similar, insomuch, as The "Symptom", is only that, and the real "Cause" of the problem, is often far removed from the actual thing we experience with a failure. I have been doing this since the Valve or Tube days, and while the circuits have gotten more complex, the principles still remain the same. and as I have found, just about every problem even though they often present the exact same Symptoms, have completely differing "Causes". and repair strategies.  People often ask me "Why" one day a seemingly, working unit, spontaneously fails. Well really the answer is simple, it is the electricity going through the unit, this electricity, is constantly "Stressing" all components, some more than others, every time you turn the unit ON, there is a phenomenon called "Inrush Current" now this "Inrush Current" can be Very High, and over time this, occurrence eventually destroys some components, as well all this all components get hot, it is a function, of it working. The Thermal stresses, caused by heating up & cooling down, will eventually destroy even the hardiest components, & some are more susceptible than others. Nearly all circuitry is interconnected to each other, and a problem in one area, will often cause a problem, seemingly unrelated in another. You see the thing that fixes most units, is Experience, gained from years of actually "Doing it" and as one goes on, patterns develop that will get you into the "Area" of the problem, where you then have to test Component, check the Voltages to find the problem. Sometimes even with years of experience, it is still UN-fixable, and the cause unknown, for many reasons, often unavailability of parts. cost of parts In the "Old" days we were trained to design a Machine to last for at least 20 years usage, and design in a 40 year parts retention. However that simply is not practicable any more, and now production runs are done, with perhaps a 5 year life cycle, and without any regard for "Spares" at all. As, the manufacturer doesn't want you to "Repair" the unit, they want you to "Replace" it or "Upgrade" to a newer model. As they see it, and maybe rightfully so, that when a unit is "Fixed" it is still a "Fixed" unit. Meaning, that once, a unit has failed, once, it has stressed, almost every other component, as well, and it WILL, in all likelihood, fail again, in the not too distant future. Not all, "Fixes" will have this result but enough to warrant the "Approach" taken, right or wrong. "They" are trying to give you the "Best Deal" which to "Their" mind, is a "New" unblemished, UN-repaired, unit. (As an aside here often the units go "Faulty" before they even leave the factory, and are "Fixed" and put back into service, waste not want not?) So all in all, it is indeed a great achievement, with all things considered, that the units we all love and use so much, even go, and keep on going, at all. Now some "Repairers" use what we call a "Shotgun" approach, and that is to replace each and every component in the area they perceive the fault is. This often results in a seeming, "Fix". However IF the actual "Cause" is NOT found, then the "Symptom" will simply re-appear, as soon as those components that were replaced, break down. The proper approach, is to find the actual "Fault" and repair that, then repair any "Damage" done, that was "Caused" by said "Fault" this is the ONLY way, an effective, and long lasting repair can be made.
This details will help you to understand the problem and let you decide,whether to get the unit repaired or go for new unit.