Tascam no longer distributes service manuals directly to end users (they refer you to authorized service centers). However, the CD-401 MkII is old enough that scanned copies are available online.
The Tascam CD-401 Mkii uses a Class 1 laser product. The manual explicitly warns against adjusting the variable resistors (potentiometers) on the laser pickup block without proper measurement equipment. Adjusting these blindly can instantly kill the laser, rendering the unit unfixable (as replacement pickups for this era are becoming scarce). Tascam Cd-401 Mkii Service Manual
The Tascam Cd-401 Mkii Service Manual is an essential resource for: Tascam no longer distributes service manuals directly to