Mistake #1
I bought a Merlin Legend system on Ebay, and while researching it, I noticed that it didn’t come with a processor board. No problem, I see a cheap processor board as well, I’ll just grab that and pop it in when it all arrives. NOPE. The reason why the chassis I got didn’t have a processor board wasn’t because someone was mixing and matching parts, it was because it was an EXPANSION chassis, and those do not have the special slot for a processor to fit.
Notice the difference between the two backplanes above? The first one is the expansion chassis with all the same board slots (except the power supply slot), whereas the second one, the “main” chassis has a processor slot with a longer edge connector. Yup, I saved a few bucks buying a cheaper setup, but had to buy a different backplane AND a processor card to actually make it all work (worth it anyway; the original chassis I got had all the specific cards I wanted).