Always disconnect a Eurorack case from mains power before opening it or moving any module

The Doepfer A-100 manual makes this a non-negotiable safety rule: before opening the case, or moving/removing/replacing any module or blanking panel, take the mains power plug out — because the internal power supply carries dangerous voltages. It applies equally to removing or replacing any panel. This is the first habit of hands-on modular work: power down and unplug before any physical change to the rack, then reconnect and switch on only once everything is installed and secured. Empty rack spaces should also be filled with blanking panels and covers fixed before use.

Examples

Correct sequence when adding a module: unplug from the wall, do the physical install, screw everything down and refit covers, then plug back in and switch on to test. Never hot-swap a module or ribbon cable on a powered rack.

Assessment

State the single action that must always precede opening a Eurorack case or moving a module, and explain why the internal supply makes this mandatory rather than optional.