What was found
CABIN ALTITUDE EICAS WARNING CLIMBING THROUGH 10,000 FEET OUT OF KGSO. LEVELED THE AIRCRAFT AT 10,000, RAN QRH, CONSULTED GOC AND GSO MAINTENANCE. TRIED BOTH AUTO 1 AND AUTO 2. THEN MOVED THE CONTROLLER TO MAN. WERE STILL UNABLE TO CONTROL THE PRESSURIZATION. RTB TO KGSO. PRESS DIFF WAS AT MAX. CABIN ALT WAS PRESSURIZED BELOW SEA LEVEL. PER CREW DEBRIEF, FLIGHT CREW HAD SOME SUCCESS CONTROLLING PRESSURIZATION IN MANUAL MODE. AT 10,000 FEET DURING TROUBLESHOOTING- IN-FLIGHT EMERGENCY DECLARED DIFFERENTIAL GUAGE - RED INDICATION CABIN ALTITIUDE- BLUE OFF INDICATION RATE GUAGE- 0 OUTFLOW VALVE- CLOSED AIRCRAFT CONFIGURED IN AUTO 2 CONTROLLER MODE, AUTO 1 - NO CHANGE MANUAL MODE- ABLE TO MOVE OUTLFOW VALVE, CABIN RATE INCREASED, DIFFERENTIAL OFF DECREASED. R&R RELAYS K149 AND K207. R&R #2 CABIN PRESSURE CONTROLLER. R&R #1 CABIN PRESSURE CONTROLLER. R&R PSEU.