890FX is AM3+ Compatible?

[nex_73]

Ok, a little more info from kinc

Featured AM3 processors such PII X6 uses 938 of 940 AM3s connection entries (two of which were never and are not routed by default, except the cards ASUS lists in their press release). AM3 + socket has 941 connections. AM3 + CPUs, however, has 940 connections, the exact same number of AM3 socket. Hence it is suitable even reasonable physical. Just be aware that it "only" works in practice with the motherboards on ASUS list.
Important to say is that it's only those who work when they have the correct routing to the power circuitry to operate a AM3 + CPUs.

So there you have the explaination to why it doesn't work on ex: gigabyte boards before v3.1
Asus has routed the extra am3 socket pin-holes on the listed models, where the other manufacturers have not.