MP 1,1-5,1 Mac Pro 4,1 updated to 5,1 won't boot and blinking light

[drfreud]

Hello.

Something is broken I just don't know what

I have 3 units of 4,1 cheese graters updated to 5,1 and running on x5680 processors, one has dual processors and two a single one, the one that stopped working has a single processor tray.

As I have other two units I could test, so I'm certain that the PSU is ok, the processor is ok, the ram sticks are ok, the video card and the drives are fine too as well as the motherboard. There's something with the tray.

I tested with other working processor, and repasted, with no luck, the processor is fine.

It seems like the memory can't be recognized, it has the same behaviour (the faulty tray) as if I connect another another tray with no memory.

The socket died? Some diode or capacitor went sour?

What could be the problem? Or, better, the solution?

I ran out of ideas

Thanks

 

[KeesMacPro]

Sounds like you answered your own question:

There's something with the tray.

Have you tried troubleshooting as described in the Technician Guide (you can download)?
There are several LEDs on the LoBo and the Processor Board that indicate defective parts when you power the MP on.
Maybe you could also check the NorthBridge rivets that hold the NB heatsink.