iMac G5 dead, Apples troubleshoot suggests logic board, new logic board also dead

A family friend has an iMac G5 which just totally died, i.e. nothing happens when you press the power button.

I followed this apple troubeshooting guide which suggested it to be logic board failure.

In some crazy coincidence I had a spare logic board for that computer so swapped it in but it still has the same symptons. This surely suggests power supply rather than logic board. However why does the apple knowledge base article say it is logic board.

I tried taking the additional components out to see if it could be another issue e.g. superdrive, harddrive etc but it doesn't do anything even when it is just the logic board and power supply.

I am not sure if it is worth repairing this machine I found the part on a website for £180, or one from iFixit for about £130 and some on ebay for about £70.

Could it be anything other than the power supply? Is there a way I can test the power supply to confirm before ordering the new part?

It is the ALS, although I did shoe horn a pre ALS logic board in there to try and spark it back to life.

In that troubleshootnig guide it runs through the leds and it suggets logic board failure. i.e. LED 1 on with the power connected but no other with the internal power button pressed. I tried with different power cords and in different houses.

I may take the PSU apart tonight to see if any of the capacitors went pop.

I forgot what a dream these iMac G5s were to take apart, having recently taken apart an C2D iMac it is a right faff where as these G5s a few screws and you are in, a few more screws and everything if off.

Looking at the caps there are a few bulging and a couple of those have leaked a bit through the top surface.

Most likely the cause of the failure. There is also some sorching on the underside of the PSU case in the bad cap area.

The caps look like a nightmare to replace as they are all covered in this grey gloupey material.

Either PSU replacement and hope it was just that or a new machine.