4-bit Homebrew CPU - counting test

This is an extremely primitive CPU I've been stressing over for the past week or so. It operates on 4 bits at a time, but the accumulator, program counter and Index registers are all 16-bit. It is running a simple increment program to make sure the accumulator and addition logic are sane. It works by shifting the accumulator through the addition Finite State Machine. There are two blown segments on the LED display. I'm aware my desk is a mess. I am now calling this processor CADET, after the IBM 1620 which used lookup tables to do arithmetic (same as my machine). It stands for, "Can't Add, Doesn't Even Try." http://kaput.retroarchive.org/CADET/