6i24 and boot / gpu

Hi Peter.

I have an existing 5i24 which is working fine.
I bought a backup 6i24 for redundancy a number of months ago, but have not used it as yet.
Today I was going to flash the 6i24 with the 5i24 bin file. Jumpers are configured to mimic the 5i24 board.
So I took the 5i24 out and put the 6i24 into the single lane PCIe slot.
Problem is that the computer goes through the BIOS flash, but then hangs on boot.
I have tried various other PCIe slots on the motherboard (single and multi lane) without success.
When I put the 6i24 board in I see LED's light up briefly, then immediately extinguish.
I put the 5i24 back in and the computer boots fully, and --readhmid reports correctly.
It is almost as if the computer thinks the 6i24 is a GPU and hangs there on boot because it isn't.
There are no BIOS settings to force the computer to ignore a GPU or to force it to use on-board graphics...
Peter, have you struck anything like this before, and do you have any suggestions?
Many thanks,
Marty.
 

I haven not seen this kind of issue but sometimes, motherboards with x4/x8/x16 slots
won't work with a X1 card. Also make sure that the 6I24 is jumpered for 33 Mhz clock
(and all jumpers match the default jumper positions in the manual page 4.