The parts you will be replacing are on the large heat sink on the Main Board. The part number of these IC's is STK392-110, they should be replaced with STK392-150 or -180, these are higher capacity IC's.
You have to find all of the Phillips screws that secure the board. Some are around the edge, but a couple are in the middle of the board, and three secure the heat sink, which has the STK chips that you will replace. The STK's are held to the heat sink with two screws each.
Now you have to pry up the white edge connectors that connect this board to the adjacent boards. They can be a bit stubborn, use the tip of a flat blade screwdriver to help do this.
Disconnect all of the connectors that go to various plugs on the board. They can only go back one way, so you don't have to pay close attention to which one goes where.
Once you've done all the above, you will see there are some plastic tabs on the front of the plastic tray that the boards are mounted on. You should be able to push on those and have the board come out easily. Do not force it, it will come out with no resistance if you have all the screws out.
Remove the Power board and look for the 5 amp fuses F9A04 and F9A05, they are near the power transformer, and are about the size of a grain of rice. They are soldered in, replace both of them (even if one checks good). You can order the STK chips from MCM Electronics by that STK number, and a box of five 5 Amp Pico Fuses with part number 28-0636.
Then just unsolder the old STK's, install the new ones and carefully solder them in, and make sure the new IC's have sufficient heat sink compound on the back of them (available at Radio Shack), reassemble it, and you should be good to go.
When you reassemble it, pay attention to the white edge connectors that you pried up during disassembly. When you push them back, many times not all of the pins will reseat properly. Run your finger across the tops of the connectors. If one pin didn't seat, you'll feel it immediately.
As I said, you also need to be able to solder and unsolder neatly and carefully, and if you've never done that before, you'd better practice this first on a junk PC board.
You are going to need a small pencil soldering iron (in the 25 watt range), some electronics solder (not the same thing that plumbers use), some desoldering braid and some silicone heat sink compound. You can get all of this at any Radio Shack.
Take the soldering iron, and once it's hot, you must "tin" the tip with fresh solder. Put plenty of fresh solder on the tip, then shake off the excess Then, just carefully place the tip on a piece of desoldering braid and put that on one lead from a convergence output IC, feed a little fresh solder onto it, and the fresh solder and the solder on the IC pin will wick away by capillary action, leaving you with just the pin of the IC unsoldered from the pad it was soldered to. This is going to take some patience and practice, and you should use a magnifying glass or very strong reading glasses when you do this.
Once all the pins are unsoldered, you can remove the screws holding the IC to the heat sink and remove it. Take a new IC and spread a thin layer of heat sink compound on the back of it, then mount it on the heat sink. It will be tricky getting all the pins to go through the PC board without bending, but with patience, you'll get it.
Now "tin" the soldering iron tip with fresh solder again. Put plenty of fresh solder on the tip, then shake off the excess Then, just carefully place the tip on one lead from a convergence output IC, feed a little fresh solder onto it, then move to the next pin and repeat. After you've done 4 or 5 pins, take the iron away and re-tin the tip with plenty of fresh solder and shake off the excess. You may want to wipe the tip off with a rag before putting fresh solder on the tip.
Once you're done, carefully check your work to makes sure you didn't accidentally solder two adjacent pins together. If you did, just use the desoldering braid to suck up the solder, and reapply new solder.
Once you're happy with that, reassemble everything, cross your fingers, and see if it works!
Let me know how that sounds or if you need more advice.