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On rare occasions the tape will become caught in the tape path after threading. This usually occurs because it was not located correctly inside the cassette lid (pocket) prior to cassette insertion. This error can cause bad things to happen. In this discussion I am going to cover the results of the types of threading errors, what to do when they happen and how to prevent them. Start by looking at the photo above. It illustrates the position of the tape (shown in red) after it has successfully traveled into the correct position inside the 711 chassis assembly. It starts at the no. 1 guide, goes around the video drum (rotating head disk assembly also called the scanner) then on to the capstan shaft and then exits at the No. 10 guide. The machine must position the tape exactly this way every time it loads. If it fails to do this the tape will usually not move or not move properly. Damage to the tape usually results and sometimes the machine suffers too. Threading has to be carried out with precision and accuracy, and within a certain time frame. If it takes too long it will be aborted and the tape will retract and the cassette will eject, if it can. Threading (loading the tape) only occurs after the cassette has been accepted and reaches the fully down position. Once detected the pinch assembly (mounted on a toothed sliding gear) moves to the right and locks into the ready position. It carries with it the pinch roller and the number nine guide (roller). (Travel is shown by the blue arrows going to the right.) The pinch roller is now across from the capstan. At the same time the shuttle block assembly, with the number four and five guides on it, scoots to the left and goes clockwise until it assumes the position in the upper right. It too is shown here securely locked in place. (Blue arrows going to the left.) While it is moving the tape is smoothly wrapped around the video drum. The completed process now has positioned the tape for traveling around the video drum when pulled by the pinch roller and capstan. All the guides and mechanics are precisely located and tilted to maintain stability and control. Now click the picture and you will see the shuttle block with the tape positioned as it should be. It must be like this every time. Most of the problems with threading occur at the shuttle block. I am going to cover this first. (For clarification the tape is the shinny black ribbon of thin material that was shown as red earlier.) After threading the tape travels in the following manner. It goes past the number four guide, around the number five roller (which is adjustable so it has a slotted head with a set screw in the middle). From there it goes past the full erase head (black housing with the copper wires inside that excite an electromagnet). Next is the number six guide. It has the nut on top and it too is adjustable. From there the tape is spooled around the video drum. With that in mind click on the picture and set what happens then the tape gets loose inside the cassette pocket and the tape gets pulled out of place. In this example the tape missed the shuttle roller altogether as it was being pulled out of the cassette. The tape is now incorrectly positioned on the number four guide. Located like this there will be a snowy picture and the capstan will exert a lot of labor trying to move the tape. The number four guide is not a roller and the friction at this tight angle is very high. Fast forward and rewind with be difficult if not impossible. If eject is requested the tape might not make it back into the cassette shell. If it gets caught the machine will try rethreading. If you try eject again, it might repeat but will eventually shut down. The only buttons that will respond after all this will be the ON/OFF and EJECT. Sometimes the machine may go into stall mode. This is slowly moving the tape forward in an attempt to get past the problem area. The reaction can vary depending on the model. These protection routines are there because Sony engineers foresaw the possibility of a tape error and built into the programming a faulty loading routine to shut down most of the functions.This usually occurs after only a few seconds of inaccurate operation. To get a tape out that is trapped in this way requires UNPLUGGING the machine, removing the cabinet top and gingerly pulling the tape off and away from the number four guide and placing it over and onto the number five guide (roller). A cue tip or paperclip might help. Note: Before attempting any internal repairs yourself I repeat: ALWAYS UNPLUG the machine to avoid getting a nasty electrical shock or the worst, electrocution by the power supply. Keep in mind the power company can deliver all the voltage needed to fry you.
(Unplugging also resets the machine.) The section of tape that is moved around is usually damaged. If it is too bad it should not be used again. This is to protect the delicate video heads. If you click on the photo again you will see another type of threading mistake. This one is more complicated. Here the tape has been wrapped around the number four guide as well as the number five guide. This results in it becoming double wrapped around the video drum too. This one is rare but when it happens the unit usually shuts down midway through the threading process, it seldom makes it all the way around the drum as it is shown here. Trying to eject the cassette on this one is almost never successful. Once again the tape must be manually removed. Sometimes cutting it will be necessary. So what causes these failures to happen? In most cases improper threading can be traced back to a tape that was loose inside the threading pocket of the cassette. To explain this there is another picture. Click now.
Here are three cassettes showing the triangular shaped threading pocket with tape located in different positions. They are shown from the bottom with the cassette doors partially open so the tape can readily be seen inside that special pocket. The rear one has the tape positioned in the proper location, laying straight and flat against the center tape support (tab) and holder. When the lid is closed the tape will be securely stationed inside a trough or channel formed by the lid and two short walls inside the lid. They make for two channels. Only the backside of the tape touches the walls or support, not the recording surface. It also lays against the smooth interior of the lid. The other two examples are showing the tape out of place. The one in front has the tape located behind the channel in the lid instead of inside it. It will most likely miss the shuttle or pinch roller assembly when it's loaded. The middle example shows the tape positioned behind the center locator (tab or tape support). This is the most common error. This one will get the tape caught when it's ejected. An illustration of how it looks once inside the machine is shown is in the next photo. (The cassette lid has been removed here to better see the tape dislocated.) In this case the machine will not know something is wrong until a function is requested. The tape will drag and damage will occur. Shutdown occurs in most of these cases. During eject when the shuttle and pinch roller return to their parked positions and the tape will be caught by the moving components. The loader will try to lift the cassette up but it can't. Ejection will stop, reverse and it will try to thread the tape again. This cycle might be attempted several times and but eventually the VCR will fault out (shutdown). Removing the cassette is similar to the methods already discussed. The section of tape involved will be ruined. So why does tape become loose inside a cassette and cause these problems? Thankfully tape loading failures is rare but the common cause is it has become loose inside the cassette pocket or shell. This could be cause by the machine that previously ejected the cassette. One that didn't fully draw the tape back into the cassette before it was ejected. This indicates a reel table problem or interference issue. Improper handling is also a possibility. Another is the use of a pop-n-stop rewinder that jerks the tape when it stops. This can leave a cassette with too much tape slack inside. It's really hard to pinpoint the exact reason, only the result. Here are several ways to reduce the probability of these mis-loads. Always keep your machine in tip top condition with regular service. Don't rewind of your tapes in your machine. Use a smart rewinder, one that senses the tape rotation rather uses a lever against the tape to pop open. The final and best way to avoid loading and threading problems is to turn the cassette over prior to insertion and verify that the tape is positioned correctly within the threading pocket cavity, with no bulges, billowing or looseness. Should you find any, turn one of the reels to take out any slack. (I sell a tool for doing just that in my "Betamax Accessories" section.) If the tape is behind the center locator tab, flip the lid open and gently slip it back into position. This inspection routine is also a good way to keep track of how well your machine is performing during rewind, fast forward and eject. |