For its full fiscal year, Digital Equipment Corp. reported a 38% increase in net income to $617.4 million from $446.7 million a year earlier. Revenue rose 14% from the year before. Digital said its fourth-quarter profit was up 138% from a year earlier. Analysts said the Maynard, Mass.-based firm's strong performance this year came from the complete, 20-month overhaul of its VAX line of minicomputers. "What we're seeing now is the payoff from an enormous investment and disciplined pursuit of a 15-year strategy that has given us a single family of truly compatible products," said Kenneth Olsen, Digital's president.