I started building the control unit on perfboard but didn't get very far with the soldering before taking a break to do a different project. This (unrelated) project used professionally made PCBs and was so easy to build it made me stop and think about using PCBs for LEO-1. After having great success and ease of construction making the Register Unit and ALU on individual PCBs, I decided to start the Control Unit again and do it on a PCB as well. This is now finished. I tested it in steps as I populated the board, making sure that each section was working before proceeding to the next. That way, if something didn't work, I would have a good idea of where the error was. Eventually I connected it to the memory board and tested the instruction fetching. When it seemed to be working, I connected it to the ALU and Register boards. It seemed to 'just work', although it would be a few weeks before I ironed out all the teething problems. Most of these problems were on the register board though.