During recording, playback, rewind, fast forward and the other various video operations the tape is in constant contact with the video drum. It stays wrapped around it and held in position by the various guides. The top part of the drum is named the upper drum and the bottom half is called the lower drum. The upper drum is machine sot have microscopic grooves around it. This is so the tape can ride on a cushion of air as it travels around it. The lower part has a tape rail machined in it that spirals around and down. It is pointed out in the above illustration. This raised metal control the location of the tape on the drum as it is scanned and it is a uniform standard. The upper drum has two tape retainers projecting from a plastic hold down assembly. Its job is to further insure that the tape stays positioned against the tape rail at all times. Especially during spirited operations like reverse Betascan and BetaSkipscan. Remember with the Beta format the tape is able to stay threaded in the path during all of its functions. This is because the Beta tape paths overall friction is so low. It is always ready and able to perform playback functions at the press of a button. This is something that VHS was unable to do. But there is a downside to all this. Because the tape is always in contact with the drum (and other path components)* there are areas that eventually start to wear over use. This is why I recommend a rewinder be employed for all extended winding. This greatly helps to prolong the surface of the drum (along with the ACE assembly, video heads and other tape parts). Looking now at the photo above you'll notice the shiny smooth surface that has developed. When it gets too polished this slick area will cause the tape to contact too large a surface area and it begins to drag. (It also increases static charge which further increases tension and causes other problems.) This doesn't usually effect play or record but it does make for labored rewind, fast-forward and scan. If it gets too smooth it can prevent tape movement altogether. Machines with the double pancake type assemblies are especially sensitive to excessive tape drag. They will start intermittently shutting down during winding because the electronics senses the excessive load. This shows up as a noticeable flipping or popping of the tape. The solution is to burnish the upper drum or replace it. This restores the friction characteristics and reduces the drag. Click on the photo to see what restored upper drum looks like. All the Betas I refurbish or repair have the upper video resurfaced or replaced. Why does video recording require a this special video drum device, called a scanner, to record a picture? It is because of the high frequencies necessary to record the large amount of information needed for producing a video image. It is much more than the typical linear system can handle. To get a better understanding of this process and how it is applied to home video recording click here Now move on to the ACE ASSEMBLY, click here. *There are exceptions to the tape staying in the machine, most Sanyo machines wind it partially back into the cassette for their rewind and fast-forward modes. ©Misterßetamax go to homepage