GCU exitation problem in C-130 Technical Posted October 11, 2012 Having a problem with an H-model GCU. Number 4 generator was showing no volts/freqs. It was determined that the generator was fried and was replaced along with a GCU. Second gen fried. Upon troubleshooting we found that the GCU had an output of 50 vdc to the exitation field. The GCU is getting 106 vac from the PMG. All wires have been ohmed for shorts to ground (none found), breaks, etc. None found. All grounds have been checked and found good. Slaved #3 GCU into #4 harness and had the same exitation output of 50vdc. Put #3 GCU back on it's proper harness and it checks good. #3 gen PMG is 96vac. Slaved #3 gen PMG into #4 (isolating #4 pmg wire). Still same output of 50vdc on #4 exitation. Has anyone encountered this or a similar problem? Any possible suggestions?