"BRANCH ." is always a good one - 0777. If that runs, much of the CPU is functional, and any errors found from there should be pretty easy to track down. I'm assuming you have the 'Programmer's Front Console', the one with the 0-7 number keys, etc? If you have the simple one, instead, that uses a program in ROM to drive the console serial line, and most of the CPU has to be running to use that. The Programmer's Console is pretty simple. Key in the address, hit "LAD" (Load Address), and then you can read ("EXAM"), store ("DEP" - after entering the number you want deposit), or start the CPU running at that address (hold down "CNRTL" and "START"). Hitting "EXAM" multiple times examines successive locations - "DIS AD" will show you how far it has gotten. If the CPU is running ("RUN" light is on), pressing down "CNRTL" and "HLT/SS" will halt it. Load, deposit, etc don't work unless the CPU is halted. Noel