This may be unrelated, but seems that a Tektronix disk controller board I found when going through my shop might be related to the graphics terminal. Hadn't found Tektronix section on bitsavers prior to this post and drew a blank searching internet. Manufacturing dates on chips are 1980 and it's a Disk Controller J6928-01. It has 8 EPROM's which have labels that range from 160-0956 to 160-0963 where it appears that last 2 digits indicate bit position stored in the EPROM. Has NEC D765C chip which is a floppy disk controller and suspect that I knew this 35 years ago as was in proximity to an 8" floppy drive that bought. Have no idea what piece of Tektronix equipment it came from but it's available to a good home if anyone in need of it. Hadn't looked at old Tektronix test equipment for decades and remember seeing a lot of it in labs but generally beyond our research budget althought it was very well made and worked for decades.