HP2648A tape drive capstans

If it's the sort of drive I think it is (alas I don't have this HP terminal, wish I did...), it works like a QIC tape drive. The motor spindle has a rubber wheel on the end (this is normally called the capstan), this turns a hard roller (normally called the drive puck) in the catrridsge, which then moves the tape by an endless belt that runs between the 2 spools of tape. We had a discussion some months back about how this actually tensions the tape (I understood it in the end, it depends on the fact hat the belt stretches slightly). The is no capstan/pinch roller like in an audio tape recorder [1]. The roller that fails is the rubber coated one on the motor spindle, part of the drive. I have worked on 2 HP tape drives like this. One is the type used in the HP85 computer. It has a PCB fixed to the back with an HP custom chip on it. The other is the one used in the HP9815, HP9825, HP9845, etc computers. It has a PCB attached by wires with a few standard ICs on it (a TTL decoder chip, 2 or 3 op-amps). [1] My HP9830 has a built-in tape drive that takes tapes that look like audio compact cassettes. But there's no pinch roller and capstan, the only drive is to the spools. And I amp pretty sure this is nothing like the drive in said HP terminal. -tony