Replaceable unit, image forming apparatus that incorporates the replaceable unit and method for attaching a part to the replaceable unit

A method for mounting a circuit board into a recess formed in a replaceable unit, the circuit board including a first edge, a second edge, a third edge, a fourth edge, and electronic components mounted thereon, the method comprising:

• inserting the circuit board into the recess with the first edge and the second edge abutting first and second positioning portions, respectively, formed in a perimeter portion of the recess;
• and
• inserting the circuit board further into the recess in a direction substantially perpendicular to a direction in which the first and second positioning portions are aligned, the circuit board being inserted until the third edge enters under a third positioning portion formed in a perimeter portion of the recess;
• mounting a retainer into the recess such that the retainer abuts the fourth edge and a portion of a major surface the circuit board in the vicinity of the fourth edge is under the retainer.