Apple LaserWriter 12/640 PS - Manual (Page 311)

Cleaning the exterior
Unplug the power cord and then wipe the exterior of the printer with a clean,
soft, damp cloth. Use a mild soap or detergent if necessary, but never use
an ammonia-based cleaner. Be careful not to get any liquid in the power
cord port.
WARNING Never use ammonia-based cleaners on or around the
LaserWriter 12/640 PS. They may react chemically with the toner
and with the printer’s plastic case.
286 Chapter 11