What was found
Approximately 2 minutes after takeoff, had gear tone and other failures: 1) norm anti-skid fail, 2) proxy system "A" fail, 3) HYD qty "A" fail, 4) ground spoilers not stowed. Apparent proxy system "A" fail or total proxy computer fial. Normal landing extension not available. Landed with alternate gear extension. Removed and replaced PSEU IAW manufacturer's instruction. Ops checked all affected systems IAW manufacturer's instructions. Ops check good. Released aircraft for flight.