What was found
DURING FLIGHT 2737, LT DPU C/B POPPED. LEFT SIDE DPU 1 (G-18) CIRCUIT BREAKER OUT, (POPPED) RESET ONCE, AND POPPED AGAIN. RT SIDE HEADING (F/O) DID NOT MATCH MAG COMPASS. AIR RETURN TO DTW. MAINTENANCE REMOVED AND REPLACED NR 1 DPU P/N 622-7713-004, SN/ON 6924, SN/OFF 1347. ALL CHECKS GOOD IAW SF340 MM.