I spent a couple of painful hours trying to figure out why I was getting strange 1.3v signals on some lines that also weren't switching properly.

I was dealing with a 7402 NOR gate and as you can see below it's pinout is the opposite of basically every other logic chip I have in SPAM-1. 

Without checking the schematic I'd assumed the 7402 had the more common pinout, so I'd connected output to outputs and inputs to inputs, which helps explain why nothing was working for me last night.

There's also a reversed NAND the 7401.

So frustrating - drove me half mad.