Traditional Culture Encyclopedia - Photography major - What does it mean that Sony camera lost its drum FG?

What does it mean that Sony camera lost its drum FG?

Tape bin: the bin where old tape cameras put tapes, some of which are called card holders;

Magnetic drum: the magnetic drum is the key component of the camera, and the magnetic head reads or writes audio and video information on the magnetic tape;

FG loss: It's a signal (I wonder if it's a speed signal? ) I lost it.