There are probably enough DIY manuals on how to replace those bad capacitors
in the G5 imac model...
If not then this will maybe help..

Symptoms:
If you're Imac G5 is suffering from power problems (not turning on, standby issues, video problems and scrambled pictures. Maybe its time to check those capacitors on the motherboard)

Checking those caps is easy and takes 2 minutes: Follow step 1 and 2, and step 7 and 9 to know what to look for...

Step 1: The Imac...

The Imac G5 was was plagued with the Capcitor problems, Apple started a special warranty program to repair all those Imac's. That program has bin terminated, but I have seen the same problem with the timecapsule as well. Today there are not that many people that want to repair there imac G5 but for those, here we go...

Our victim: A "left to die" Imac G5 17." We are going to save him in a Saturday afternoon.
Here are some things we need to help him:

A LOT of space... We need to store all his parts temporary and we have to work on its motherboard.
It also keeps things organized.

Tools: These are the tools that I used:
soldering iron, screwdrivers, torx screwdrivers, anit static band, pliers, thermal compound, and replacement capictors.
Experience: Please have some, Its not difficult, but I think some is defiantly required.

Safety warning: Always unplug the power!! Even when the power is unplugged some capacitors will remain there power! In the new Imac models these power supply units on the bottom are open, and you WILL get a high voltage shock from it!! This is not the case here but be advised, if you see something and you have no idea, just stop and ask someone who does knows!

Capacitors: The ones that we are going to replace are bulging and could spit out electrolytic fluid or residue. (In fact, mine did when pulling them out...) Clean of this stuff from youre hands and the motherboard immediately!!! And wear safety goggles, the old capcitors are under heavy pressure, if they burst right in your face then... Well, youre not becoming any more attractive from it...

Step 2: Get Started...

Open the Imac:
Open your imac by turning the three screws on the bottom al the way tho the left. These screw wont come out but they will unlock the back. you can tilt the back off by lifting it up at its foot.

Here is a basic overview of the imac, now you know what to exspect.

We will start at the cd-drive:
Just undo the the three screws around the drive. When your done pull the drive out by
the white label on the right. I have also removed the memory already, I dont think I have to
tell you how that is being done... Come on, you have to be a geek to follow this instruct right?? RIGHT???

Step 3: Airport, Fan Board and Harddrive...

Airport and dail-up modem:
Pull out the antenna from the airport, you must do the same thing for the dail-up modem.
What the.... who uses these things anyway?
Pull the airport out, then the grey plastic bracket. After that, pull out the dail-up modem.

Fan board
Two screws, I say no more...

Harddrive:
Remove the sata and power supply cable on the left of the drive, then undo the three screws around the drive. Dont forget to unplug the temperature control cable that leads to the motherboard. Keep the cable with the drive to make it easy later on...

Step 4: Power Supply and Inverter...

Power supply and cable:
Turn the three screws on top of the power supply to the left.
Watch out: the screws in the power supply cannot be removed!!

Next undo the little hook on the power plug and insert a flat screwdriver like in the photo...
Turn the screwdriver in the two holes to force the plug backwards. At some point the plug let's go of the socket and you can grap it and pull it all the way back. (this can be a bit tricky)

Next you can pull out the power supply likes this:
Oh, and dont forget to turn back the slot screw back into the closed position. (to the right) This will help make space to remove the power supply.

Left inverter unit:
One screw in the middle, pop up the grey inverter and remove the two cables, leading away from it.

Step 5:

Cables and plugs:
Just to make sure, make a picture like I did of all the cables connected to the motherboard.
They are made not to fit in a another socket then they where designed for. (still, just make those pictures, its going to save time and headeaks.)

Tip: dont pull on the cables or wires, I must insist: Use the freaking plug to pull it out.
Many plugs where destroyed by rough handeling or jurking on till it broke.
(I broke some to in the past to)

Remove any cables that are lying around in the case...

Step 6: Removing the Motherbord..

Motherboard:
Alright, here comes the big job, remove the following screws:

From left to right or see photo for details:

- On the left in the upper and bottom corner, two gold color screws.
- Between the powerplug and bad capacitors, one silver.
- Between the big fan and the video out plug, one silver.
- Between the rowes of capacitors on the bottom, one silver
- Grey air output ontop of the "G5" logo, remove the left and the right one.
- Between the "G5" air tunnel and the memory banks, two silvers...
- On the top right and bottom, one silver and one gold.

Now remove the motherboard like so:
Grab on the cooling block and the connections and pull it out like shown.

Step 7: Soldering and Replacing

Put a static free mat on the table and make sure you connected to it as well.
Then mark the capacitors on the back that needs to be replaced. That way you make sure that you dont head up or remove the wrong parts.

Capacitors that needs to be replaced are being identifed by:
top, sides and bottom bulging or leaking electrolytic fluid on the top.

I wanted to use this koper stuff, when heated up it sucks up the tin from the motherboard. but the connections are so small that it didnt work. The best to do this is to head up the tin connection point(s) of the capacitor and then pull the capacitor out of the board:

Practice on a old circuit board first, to study the technique and make it your own:
Heat up one leg, (the left) and pull the capacitor to the right. Heat up the right leg, and pull the capacitor to the left. working your way up, at some point the legs are free.
(Take your time and give the motherboard enough time to cool down.)

My problems: Well, I messed up, big time. (well, Iam human two right? (So I have bin told.)
Two legs of two capacitors are stuck in the motherboard. Luckily for me apple made a spare place for a extra capacitor. So I solderd one into place right there. Unfortunately I was forced to solder two wires to another capacitor witch had to be placed somewhere else. With some tape I insulated it an mounted it somewhere else on the board. Not really a good solution but it works.

About the capacitors: The replacement capacitors I used where from a old power supply, I didnt buy new ones. In this case it doesnt matter because there new function on the motherboard was exactly the same. I didnt have to buy very special ones, but if needed you can buy them of the web very cheap.
But please do use the same type and ratings and watch the polarity!!!

More information from Asmodeo: (many thanks to him)
I've changed capacitors in PC motherboards a lot of times, and the tricky part is desoldering the old ones. I have a method: Use a 60Watts soldering iron, applied to BOTH legs of a given capacitor at the same time. Let It heat for 10 seconds.(It´s a bad capacitor...You can't ruin It!).
Then, SLOWLY, pull the capacitor out of the board while applying heath.
To open the pad orifice where the capacitor lead was , use the copper "tail"....it is a hard way, but It is worth the effort. If the orifice doesn't clean at your satisfaction, then use a drill bit of the right size (0,5 mm is ok ) ..but use it BY HAND..make a handle for it with some isolating tape!

One thing I do not agree with You is: "put same rate capacitors"
The "capacitor maladie" is due to capacitors that are rated up to 85°C of temperature.
I always use as a replacement capacitors of the same rating in microfarads (uf) AND volts , but capable to withstand 105°C of temperature.
The difference in price is negligible.

Step 8: Put It Back Together

Before placing back the motherboard you will have to clean the cooling residue on the processor. This also counts for the cooling platform. Use pure alcohol and a cleaning tissues to remove that nasty stuff. Then put the same amound like shown on the photo here on the proccesor.
Keep it like this!!! It will spread as soon as you place back the motherboard into the mac.

Watch out for this little "light tunnel" place it back first in the proper position before you place back the motherboard. This is important, or the led indicator on the front will not show correctly.
And keep those cables in that aera clear, then place back to motherboard as you toke it out.

Now you should follow this instructable in reverse, but this time mount everthing back into place.
That should be easyer, ones youre done go to the nex step:

Watch out for:
-Do not force screws!! If they dont fit or do not go in well, you probably using the wrong screw.
Check this instuct again.
-Check if all cables are there, some cables can be stuck under the motherboard, then
you have to take it apart again.
Keep cables clear from everthing and place them correctly.
Airport bracket: Dont forget to pull he antenna trough it first , other wise you will have to take it apart again.
-If youre having trouble with the cables on top, just remove the big fan on top. It will make room for you to place those cables back.

Step 9: Testing the Unit...

Here are some photo's from the nasty caps, they smell horrible. Now you know what to look out for.

Testing
Now we have to test it, watch and stand back when you plug in the powerplug.
When turned on the mac should start normal again like it did before. Keep an eye on those new caps, if you have replaced them correctly nothing should happen. If something does happen: Smoke, strange smell, fire, exploding caps, turn of the unit immediately!! Check what went wrong and repair, and ask someone for help if necessary! (youre not alone at this)

Almost done...
When done testing: Place the lid back on the imac and turn all three screws to the right.
Congratulations, another beautiful Imac saved from the dump yard. He will be happy to serve you as your best friend for many years to come...