What it is and what it carries
The Mitsubishi Q38DB is the 8-slot base unit for a MELSEC-Q multi-CPU rack. It provides the backplane that carries your power supply, up to eight I/O or function modules, and the CPU. On the van, it's the frame you build the rest of the control system into. Draws 0.23 A from the backplane supply.
Mounting and physical fit
The unit measures 328 mm wide, 98 mm high, and 44.1 mm deep — slim enough to slip into a shallow cabinet. Mounting is via M4 screw holes or a DIN rail adapter (sold separately, part Q6 DIN 1). If you're swapping an older base, check the existing cutout against these dimensions.