If you have an invalid video reference feeding the Horus/Hapi physical Sync I/O port and have enabled it in the Easy Connect then it will blink Yellow in Pyramix.
TC ref: Connection must be enabled for Video reference.
If you don't have a valid video ref signal, disconnect TC ref from Easy Connect.
Note: TC ref option must be enabled in order to lock the MassCore TimeCode to the Horus/Hapi Video In.