iMac 2007 Power Supply Not Showing Output

I bought an old iMac for $50 a week ago and have been trying to figure out since what's wrong with it. None of the diagnostic LEDs light up when the power is connected to the computer. I have tried two separate power supplies, both of which show the same issue: no pin, when measured relative to ground, shows any output voltage. I followed the voltage chart here, but no pin shows anything on either power supply.

+120 VAC is present across the leads coming from the wall, so the board is receiving power. I tested the fuse on both, and on one the resistance indicated it was blown, so I short circuited it.

The large 150 uF, 420V capacitor on each board had positive leads that looked heavily corroded, so I soldered a new one onto one of the boards, in case that was the issue.

Alas, the issue still remains. Any ideas?