What was found
T/O ROLL IN DEN PACK LIGHT ILLUMINATED. ABOVE 10K COMPLIED WITH QRH PACK LIGHT EXTINGUISHED. PACK OPERATIED NORMAL FOR DURATION. GROUNDED - YES. DUE TO HISTORY, PERFORMED B737-800 FIM 21-53 TASK 820. BITE CHECK LEFT & RIGHT PASS-NO FAULTS NOTED. FOUND RIGHT FAN BYPASS CHECK VALVE DOOR IN PRIMARY PLENUM/DIFFUSER MISSING. PERFORMED CONDITIONAL INSPECTION REF B737-800 AMM 05-51-51-59 - PART DEPARTS A/C. NO DAMAGE FOUND. A/C CHEK AND RELEASED PER MEL 21-44A FAN BYPASS CHECK VALVE MISSING. OPPOSITE PACK OPERATES NORMALLY.