CDC Field Test Unit
This Field Test Unit connects to a Control Data Corporation Storage Module Drive (SMD), Mini-Module Drive (MMD), Cartridge Module Drive (CMD), Fixed Module Drive (FMD) or a Lark Module Drive (LMD) to perform diagnostics and maintenance. It replaces the computer and disk controller and allows a field service person to manually control the disk drive. It is normally used to debug a broken disk drive, or for head alignment.
A wide ribbon cable goes from the front the Field Test Unit to the disk drive. An oscilloscope is connected to the terminals the rightso you can see signals from the disk drive, and the switches are used to control the disk drive.