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The capstan is basically a motor with a shaft extending from the center. Together with the pinch roller, discussed in the next panel, it pulls the tape over guides one through six, around the video drum, past guide seven, over the ACE head assembly and past guide eight. For a review of the tape path open the CLEANING CHART by clicking here. It must run at a very consistent speed and, in many cases, be capable of running in reverse. To do this properly it has to perfectly perpendicular. Adjustments can be made to make it straight up and down. Too much tilt in any direction and the tape will crawl up or down and wrinkling can occur. What you see above are the two most routine problems found with the shafts of the motors (and a new one shown for comparison). The motor shaft on the right is an example of oxide and dirt build up. It can be removed with solvent in all but the most extreme cases. Sometimes the oxide can literally weld itself to the shaft. If this occurs the capstan must be replaced. If the shaft gets greatly worn or polished, as in the center example, it also must be replaced. The slick surface begins to lose its ability to evenly pull the tape. This produces tracking and stability problems, especially in reverse play. If you click on the picture you'll see the motor disassembled for examination. In the center is the armature (the round gray disc with the shaft in the center). It is a permanent magnet with six defined north and south poles or fields radiating around it. The armature (rotor) is be driven by the wire coils (stator) seen on the right (brightly copper colored). Notice the surface mounted capacitors indicated in the photo. They are used to absorb the electrical shock of the pulse generated when the electronics turns the coils on and off to rotate the rotor. If they fail an annoying, repeating burst or white line shows up in the picture. They also begin to leak electrolyte. This is a corrosive liquid which eats away the printed copper traces on the circuit board beneath them. When the circuits start failing to conduct, strange things begin to happen, such as no forward or reverse play, no rewind, or uncontrolled capstan speed. All of these capstans with surface mounted capacitors have them replaced during the refurbishing or repair process. Now on to what presses against the capstan to pull the tape through the machine. To examine THE PINCH ROLLER click here  
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