MP 1,1-5,1 09 dual tray won’t boot, help!

[pelgiu]

I bought this 2009 dual tray as non-working in hopes of being able to repair it easily. I changed the northbridge rivets and replaced the thermal paste, inspected the CPU sockets with a magnifying glass and everything is intact. changed the CPUs with a pair of 2.26ghz and a pair of x5680 tested and working. I inserted the dual tray into my Mac 09/ with flash 5.1 but the Mac doesn't post. the tray fans run at normal speed, there is no red LED on the backplane and the LED diag shows the green light flashing on "gpu_ok". I did all the tests with the GT120, with the RX580 and with an SSD in bay 1 with MacOS HS. the mac boots normally when I use the single tray. what else can I do? could the northbridge chip be burned? socket damage? Thanks for the attention.