CENVAT credit reversal required for inputs written off as obsolete; partial write-offs allowed if inputs remain usable in manufacture. Admissibility of MODVAT/CENVAT credit depends on whether written-off inputs or capital goods remain available and usable; fully written-off unused inputs and capital goods written off before use require repayment of credit, whereas partial write-offs do not require repayment if the inputs remain capable of and available for use in manufacturing.