Cisco Switching/Routing :: 7606s Power Coming From Single Supply

Having a strange issue here with an 7606-s chassis equipped with two sup720's, and two regular line cards. There is only one power supply, PWR-2700-AC. I recently builded this setup and powered it on last week for the first time. It ran fine for about 20 minutes while suddenly the chassis powered down.
 
I've checked the back of the chassis and noticed that the power supply had it's 'input ok' and 'power fail' led lit. I toggled the power switch and waited half an hour to power it on again. This time only 1 minute of joy. My first idea was the PSU due to the power fail led so I had it swapped by the supplier for another. Unfortunately, when I powered it on today, it didn't change a thing, still unexpected power downs.
 
So I've checked the following documentation: [URL] and followed the suggestion to power the chassis on without any modules in the slots. So I did that and it ran for 8 minutes only. However, the fan tray did respond properly when I removed the small thermal module in the upper right by increasing the fans to full speed.
 
Following above documentation, it points to the chassis (there is not much left). Now the real question comes, isn't there anything else that could be the cause of this?