Synths and keyboards: document hardware revision and replaced components

On vintage synths and keyboards, identify hardware revision, installed boards and significant replaced components when documentation is available.

Models with the same name may contain meaningful production changes. A replacement board may be correct and fully functional without being original to the unit.

Keep invoices and workshop notes, especially when scarce components are replaced.

Avoid irreversible updates or modifications before understanding compatibility, backup options and the possibility of returning to the previous configuration.