Hi!

I'm a bit stuck on a repair.
The motherboard is an MSI Z270 SLI PRO (MS-7a59)
It has 4 mux switches between the two main pcie connectors.
Its supposed to work like this: If there is only one gpu inserted into the top slot it has all the 16 lanes.
But if there are two gpu-s inserted the lanes from the cpu are split between them.

The problem is that the switches are stuck on, so even if only 1 gpu is inserted it only has 8 lanes and is trying to communicate over 16, so no image out, only using an X1 adapter.
I have narrowed down the problem a bit, but cant really find a solution.

The problem is that as far as i can see the only cause of the problem is that the PCH is not outputting the correct signals for the logic circuit to work.
I however have no idea how the pch generates these signals and why they are wrong.
To my understanding both PEG_MODE 0 and 1 should be either high or low.


Further findings:
In default (faulty) state if i plug in a gpu to the first slot it cant initialise, the image comes out of the igpu, the gpu is not recognised.

If i tape over the gpu connector so only 8 lanes can touch the slot, the dis gpu works.

If i short the X8_EN# to ground the dis gpu initializes, but only in X8 mode.
The second slot only works with an X1 adapter, the same as before.

So If X8_EN# is low it somehow enables the first gpu to run, but the switches still doesnt do anything, which doesnt seem right to me.


Thanks for the help in advance!