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Here is a modification that is performed under certain circumstances. It is optional to the refurbishing and depends on the ground measures employed by a particular model design. Static grounding is a preventative measure that is intended to prolong the life of the video drum bearings. The video heads are mounted on a spinning disk (used to write the magnetic information on to the moving video tape). It rotates on two caged roller bearings. In the photo above we see in the background a typical drum assembly. In the center is a mounting plate with half of the coils that form a coupling transformer. To the right the bearings are seen in their location the plate and also removed and set to one side. The gray flat ring facing forward has the relay wires (green and copper color) formed in it, these send electrical signals to and from the heads. Located just to the right of this plate is the lower drum section with another mounting plate sitting in it. This one has the bearings and shaft, if you look just below it in the bottom drum you can just see a hint of the companion piece to the coupling transformer. This is another relay disc that also has wires mounted in it. I mention these relay disks because they make possible the transference of electrical information between two moving components. There is no dedicated electrical connections made and the only surfaces touching are those of the bearings, something to keep in mind as you read on. Located all the way to the right in the picture is the bearing assembly laying by itself. Click on the picture and you will see the rotating parts (less the video head disk and motor). As mentioned earlier the mounting assembly turns on precision ball bearings, this design has a cage to space out the balls inside an inner and outer race. This is typical of bearings found in a multitude of applications. The next photo is an enlargement that shows damaged bearing races and balls. (The bearings are normally protected with a light-weight grease but these have been cleaned.) Notice that the curved race surfaces are covered (in the areas where they touch) with small pits and peaks. As the description at the bottom of the picture says this was caused by static electricity. When the bearings get pitted like this the video drum begins to get noisy. You would notice it first as a whirring or whining sound that changes pitch as the drum speeds up and slows down. If it gets bad enough white specks begin to show up in the picture. It is only down hill from there. Where does this static electricity come from and what is it? It is caused by the displacement of electrons on surfaces that rub over one another. The most impressive example is lightening, which is caused by columns of air rubbing together and displacing large masses of electrons. When the accumulation reaches a critical mass it discharges and makes everything neutral again, a lightening bolt is the spectacular result. Another example is when you slide your shoes across a carpet and touch a door knob. That crack of electricity is the release of the electrons that you charged your body with by using your shoes as an instrument to pull them off the carpet. In the case of the video drum getting charged, it happens as the video disk slips through the air and the tape rubs against the surface of the drum. The solution to the static build-up is to give the charge someplace to go before it reaches the critical point and fires a lightening charge through the bearings. When it happens repeatedly the arc deforms the metal surfaces. Arc welding is occurring. Small to be sure, but each time it happens a small amount of metal will be pulled away from one surface and deposited (welded) on to the other. This causes pit and peaks, the evidence of this is shown above. Now click on the picture and examine the fix. This has to be done before the drum becomes noisy, it is preventative. This is a ground strap that makes a bridge between the rotating center hub with the video disk and the stationary drum (the case ground). Sony once made a modification repair kit for this but never put a ground strap into production. They opted for stationary case grounding and discharging air dams in front of each video head. The strategy worked but nothing is perfect. Almost all other manufacturers have discharging grounds as part of their drum assemblies. Click on the photo and you'll see an example of the modification done to a Sony drum as well as the ones used by the other Betamakers. To proceed to the next section that describes the EXTERNAL CLEANING AND RENEW click here.
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