trying to fix a dinosaur, will a 3400+ amd cpu run 3500+ motherboard with the bio for the 3500+?
if not can I just add the bio chip fromm the old 3400+ to the new 3500+ board?

By "bio" I assume you mean bios?? Swapping bios chips is a very bad idea indeed and should never ever be done.
Try the CPU, it may well work fine. If it doesn't, it wont damage the motherboard (unless the CPU is faulty).

Be a part of the DaniWeb community

We're a friendly, industry-focused community of developers, IT pros, digital marketers, and technology enthusiasts meeting, networking, learning, and sharing knowledge.