Large Black Horizontal Bar

[vts1134]

Howdy gents. I am currently repairing a GE HM-171 (restoration will come after repair). The set had been heavily worked on before, and came to me with some problems. I've been working through and correcting the issues one by one. Everything I've corrected so far I've either seen personally, or read about here on the forums. I've now run across one that I'm not familiar with. When I feed the set an RF signal I get picture, but there is a large black horizontal bar across the middle of the screen (approximately one third to one half of the raster's height). It's almost like some one is censoring out the middle of the picture. I believe the problem must be coming from upstream of the detector as I can get a picture free of the black bar by injecting video there. Has any one seen this before? Any ideas on what it could be?