What was found
PDX FLIGHT NR 2266, AFTER START WHEN BLEED FLOW CONTROL KNOB SELECTED TO 11 O`CLOCK POSITION OR HIGHER CABIN PRESSURIZES/DEPRESSURIZIES AT INCREASING RATES AND SPEEDS (500' UP/DOWN THEN 1000'). WHEN KNOB SELECTED TO MANUAL, AIRCRAFT PRESSURIZED AT 2000 FPM. MAINTENANCE REPLACED CABIN PRESSURE CONTROLLER IAW DASH-8 200 AMM 21-30-06, PAGES 401-404. STEP 4B ON PAGE 404. COMPLIED WITH FUNCTIONAL TEST OF THE PRESSURIZATION CONTROL SYSTEM IAW TASK 21-30-00-720-801. AIRCRAFT RETURNED TO SERVICE