The yellow encased object is a video field delay line. It’s a fixed delay (mechanical / acoustic) that allows one field of an interlaced NTSC* picture to be overlaid on the other in case of a tape dropout. They’re normally found inside VCRs. Why do these monitors have them?
This set of ancient monitors eventually got too tired to really work and may be up to 17 years old. Not a bad run really.
*Never Twice the Same Color.