In article , "Nigel Cook"
wrote:

The right voltage to this motor but it is lacking torque...

Sony has had this problem with reel motors in many of their machines,
including DATs and camcorders. The only fix I know of is a new motor. I
think the permanent magnets get somewhat demagnetized over time, but
anyone can feel free to correct me on that.

By the way, I once owned a DTC-690, and I wouldn't recommend putting much
money into one. They are very poorly made and have a lot of problems,
especially tape transport problems. They sound good when they work,
though. There was an update kit that fixed some of the transport problems,
so maybe yours has it installed, in which case it might work OK. I hated
mine, though.