What was found
(CAN) ON FIRE ACTION, NOTICED THE NR 2 ERPM GAUGE HAD BACKED OFF TO 13200 RPM. TIT, HP, FF AND HERTZ ALL READ NORMAL. THE MEL REQUIRES 4 ENGINE TACHOMETERS FUNCTIONING, ELECTED TO SHUTDOWN ENGINE 2 IAW SOP. SECURED ENGINE, COMPLETED ABNORMAL PREAMBLE AND 1 ENGINE INOPERATIVE LANDING WHILE ENROUTE. MAINTENANCE CHANGED NR 2 TACH-GENERATOR.